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Species diversity, distribution, and

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CONSERVATIONSTATUSOFDANISHASILIDAE(DIPTERA)

Steenstrupia Larsen, M. N. & R. Meier. Species diversity, distribution, and conservation status of the Asilidae (Insecta: Diptera) in Denmark. – Steenstrupia 28 (2): 177–241. Copenhagen, Denmark, December 2004 (for 2002). ISSN 0375-2909.

We report the results of the second atlas study for Danish Diptera. It covers the 30 confirmed species of Danish Asilidae and is based on label data from more than 4300 museum specimens. For each species we provide a distribution map and discuss its distribution, phenology, and conservation status in Denmark. We furthermore present a new identification key that not only includes the known Danish species, but also those likely to occur in Denmark based on their presence in surrounding countries. It is shown that the distributional data suffers from the kind of spatial and temporal collecting bias that is commonly observed in museum samples. Several techniques are used to remove the bias before the information is used for proposing a Red List for the Danish Asilidae. This proposal is one of the first for insects that applies the quantitative criteria of the World Conservation Union (IUCN 2001). One species is found to be Data Deficient (DD: Tolmerus cingulatus); one species is Regionally Extinct (EX:

Molobratia teutonus); five species are found to be Critically Endangered (CR: Antipalus varipes, Cyrtopogon lateralis, Machimus arthriticus, Machimus gonatistes, Neoitamus cothurnatus); two species are Endangered (EN: Eutolmus rufibarbis, Laphria ephippium); three species are Vulnerable (VU: Asilus crabroniformis, Leptarthrus brevirostris, Rhadiurgus variabilis); two species are classified as Near Threatened (NT: Choerades gilvus; Dioctria cothurnata ); and the remaining 16 species are Least Concern (LC). Three species have not been collected since 1960 and for five additional species there are fewer than 5 post-1960 records. We urge that the old localities be revisited in order to elucidate whether the species might have become extinct. An investigation into the distribution and status of the “Danish” species of Asilidae in other European countries reveals that all “Danish” species are widespread and Denmark is geographically near their Northern distribution limit. For many of the species on the Danish Red List a decline has also been observed in other industrialized countries like Belgium and the Netherlands, and in at least one case (Asilus crabroniformis) natural history evidence implies that modern agricultural practices are at least partially to blame. It is discussed why Asilidae might be one of the few Diptera taxa of interest to conservation biology.

Keywords: Robber flies, identification key, museum data, collecting bias, distribution maps, conservation status, Red List.

Marie Nykjær Larsen & Rudolf Meier: Zoological Museum, University of Copenhagen, Universitetsparken 15, DK-2100 Copenhagen Ø, Denmark.

Present addresses:

MNL: Ordrup Jagtvej 54B, DK-2920 Charlottenlund, Denmark. E-mail: mnkjaer@mail.dk RM: Department of Biological Science, National University of Singapore, 14 Science Drive 4, Singapore 117543. E-mail: dbsmr@nus.edu.sg

Steenstrupia 28(2): 177–241.

Species diversity, distribution, and conservation status of the Asilidae (Insecta: Diptera) in Denmark

MARIE NYKJÆR LARSEN & RUDOLF MEIER

INTRODUCTION

Recent decades have seen an increasing interest in the conservation of the Danish fauna and flora (e.g., Ministry of Environment and Energy 1996, Lund & Rahbek 2000). However, precondition for conserving taxa is detailed information on the diversity and distribution of species. For many vertebrate groups accurate species lists are avail-

able and locality information has either already been collected (see appendix 2 in Lund & Rahbek 2000) or is being gathered at a quick pace by projects like the Danish mammal-atlas project (Baagoe & Jensen 2000). The situation is less satisfactory for the generally much more speciose arthropod groups, which comprise most of the Danish species diversity. Fortunately, for three of the four megadiverse insect orders species cata-

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1994).

We here provide locality lists and maps for a second group, the Asilidae – robber flies. The information is based on more than 4300 specimens from the main collections of Danish insects (Zoological Museum, University of Copenhagen;

Museum of Natural History, Aarhus) and from the private collection of R. Bygebjerg. Our study augments Lyneborg’s (1965) important treatment of the Danish Asilidae, which is the main refer- ence for natural-history information and for mor- phological descriptions of the immature and adult stages. However, Lyneborg’s study only indi- cates species distributions in a narrative form, while we here provide detailed distribution maps, detailed lists of localities for all species, and discuss abundance changes over time. We also incorporate information from more than 1000 specimens that were collected after 1965 and update Lyneborg’s species key by including mor- phological characters from the recent literature (e.g., Weinberg & Bächli 1995, Geller-Grimm &

Smart 1998). This new key not only covers the species confirmed as belonging to the Danish fauna, but also those that might occur here based on their presence in neighboring countries (Pe- tersen et al. 2001).

The detailed information on the distribution and abundance of Asilidae is then used to propose a Red List. Ideally, such lists should be based on the official criteria by the World Conservation Union (IUCN 2001), but until recently there were two obstacles for cases like the Danish Asilidae.

(1) The criteria were only intended for use on the global scale and it was not until recently that they have been modified to fit the needs of regional lists (Gärdenfors 2001, Gärdenfors et al. 2001).

(2) The IUCN criteria require quantitative state- ments about the abundance, distribution, and/or probability of extinction for each species. Such data are usually not available for insects. It is only

found (Geller-Grimm 2000). The robber flies are most diverse in warm and arid regions, with species numbers rapidly decreasing toward the trop- ics and the temperate regions (Lyneborg 1965).

Denmark has few species (30–37 species; see Petersen et al. 2001) because it is close to the northern limit of the asilids’ range. Adult Asilidae prey on other insects and spiders (Wood 1981).

This predaceous mode of life is reflected in the distinctive morphology of the adults, which can be used to identify the family (see Lyneborg 1965 for detailed diagnosis). Especially conspicuous are the eyes, which are separated by the sunken vertex (Fig. 7) and provide forward- and back- ward- as well as stereoscopic vision. When prey is detected it is seized by the legs, which are unusu- ally long, robust and usually covered with bristles and hairs. As diagnostic for the family as the eyes is the so-called mystax, which consists of hairs and bristles that are found in the middle of the face and are thought to protect the eyes from struggling prey (Figs 4, 12). The mystax extends in some cases to the antennal bases (Wood 1981) and is often found on a protuberance (Fig. 12).

The victims of Asilidae are mostly insects, which are paralyzed by a neurotoxin injected through the hypopharynx. The liquefied content of the victim is then imbibed through the proboscis of the predator (Geller-Grimm 2000).

The phenology of the Asilidae in general is poorly known (Lyneborg 1965). Information about the early immature stages exists only for 16 species (Musso 1981) and complete life-cycle descriptions are restricted to four species: Pro- machus yesonicus Bigot, 1887, Mallophora ruficauda (Wiedemann, 1828), Mallophora me- dia Clements & Bennett, 1969, and Machimus rusticus (Meigen, 1820) (Musso 1978). Machi- mus rusticus is the only Palaearctic species among those and is probably for now the best model for Danish Asilidae. Under laboratory

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conditions Musso (1978) found that the eggs of M. rusticus hatch after 4–6 days, which is also the time required for the eggs of most other asilid species. One known exception is Andrenosoma atra (Linnaeus, 1758), which requires 50–56 days. The duration of the complete development from egg to adult varies between species. For example, in Machimus rusticus (Musso 1978) it was estimated to be one year and involved 7 larval stages, whereas it requires about two years spanning 5 larval stages in Promachus yesonicus (Musso 1981). Most Asilidae larvae live in dry soils (Lyneborg 1965), but for species of the genus Laphria Meigen, 1803, Choerades Walker, 1851, and Andrenosoma Rondani, 1856 the larvae are found in rotting wood (Hull 1962).

Based on the morphology of the mouthparts, Melin (1923) initially thought the larvae to be phytophagous, but his views have been rejected and the larvae are now regarded as predaceous, mostly on insect eggs or larvae of Scarabaeidae, Cerambycidae and Buprestidae (Geller-Grimm 2000). For Machimus rusticus the overwintering stage is either the 6th or 7th instar larva, during which the growth stops for several months (Musso 1978). In spring or early summer pupa- tion takes place, followed by a pupal period of 2–

6 weeks (Melin 1923).

METHODS Obtaining label data

The study was based on 3615 specimens from the Zoological Museum, University of Copenhagen (ZMUC) and 776 specimens from the Museum of Natural History in Aarhus. Of these 1050 were initially unsorted and thus identified to species with a key prepared based on the keys of Lyneborg (1965), Weinberg & Bächli (1995), Geller-Grimm & Smart (1998), and own observa- tions. This key covers all 30 confirmed Danish species, as well as 14 species found in at least three surrounding countries (Lehr 1988, Petersen et al. 2001).

All available label data for the specimens were recorded (species, locality, day, month, year, col- lector). Specimens with sufficiently precise locality data were assigned to 10x10 km UTM grids

(Enghoff & Nielsen 1977, Madsen 1999) based on “Det levende Danmarkskort” (Kort & Ma- trikelstyrelsen 2000). When the name of a locality corresponded to multiple places in Denmark or a locality was neither found in “Det levende Dan- markskort” or older maps (Geodaetisk Institut 1936, 1945, 1946), researchers at the Entomol- ogy Department of ZMUC were consulted. They could often clarify localities based on knowledge about Danish collectors and/or popular collecting sites.

Distribution maps

The distributions of the species were mapped onto 20x20 km UTM grids. Although specimens had initially been assigned to 10x10 km grid, the larger scale was chosen, because there was insuf- ficient specimen data to show reliable distributions at this smaller scale. However, all discus- sions in the text mentioning grids pertain to the original 10 km scale. “Det levende Danmarks- kort” (Kort & Matrikelstyrelsen 2000) cannot be used to assign localities to 20x20 km UTM grids.

For that reason, all 10x10 km UTM grids were converted by hand to 20x20 km UTM grids using a conversion scheme, where four 10x10 kmUTM grids were assigned to one 20x20 km UTM grid.

The collecting period of the samples covers more than 180 years (1818–2001). It was divided into three intervals with splits at 1910 and 1960 in order to divide the data set into approximately equal sizes. On the distribution maps we use seven symbols to indicate during which periods a species has been collected in the different grids.

We also list the number of specimens (including the specimens without label data), the minimum number of collecting events (excluding the specimens without label data), the minimum flying period (months in which the species was collected), and collecting period (years in which the species was collected).

In order to prepare a Red List for the Danish Asilidae, we used the regional IUCN criteria as outlined by IUCN (2001, version 3.1). We studied for each species changes over time with re- gard to the area of occupancy and abundance. For this purpose we used two time periods of equal length for comparison (1920–1960; 1961–2001).

It would be preferable to use shorter time periods,

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Table 1. Danish Asilidae (Diptera). Changes in abundance between two time periods. Figures in parentheses are relative, see Methods: Distribution maps. No. 10-km UTM gridsNo. collecting eventsNo. specimens Status of speciesChangeChange 1920–19601961–20011920–19601961–20011920–1960 Regionally Extinct Molobratia teutonus00000000 Critically Endangered Antipalus varipes5 (0.041)0-5 (-100%)5 (0.012)0-5 (-100%)5 (0.007) Cyrtopogon lateralis01 (0.005)101 (0.001)10 Machimus arthriticus2 (0.016)1 (0.005)-1 (-68%)5 (0.012)1 (0.001)-4 (-92%)10 (0.014) Machimus gonatistes1 (0.008)2 (0.010)1 (25%)4 (0.009)2 (0.003)-2 (-67%)5 (0.007) Neoitamus cothurnatus01 (0.005)101 (0.001)10 Endangered Eutolmus rufibarbis04 (0.019)404 (0.006)40 Laphria ephippium2 (0.016)5 (0.024)3 (50%)4 (0.009)6 (0.009)2 (0%)5 (0.007) Vulnerable Asilus crabroniformis22 (0.180)12 (0.058)-10 (-68%)29 (0.068)21 (0.031)-8 (-46%)36 (0.050) Leptarthrus brevirostris1 (0.008)4 (0.019)3 (137%)1 (0.002)5 (0.007)4 (250%)1 (0.001) Rhadiurgus variabilis5 (0.041)5 (0.024)0 (-41%)6 (0.014)8 (0.012)2 (-14%)6 (0.008) Near Threatened Choerades gilvus12 (0.098)10 (0.048)-2 (-51%)37 (0.086)13 (0.019)-24 (-78%)49 (0.067) Dioctria cothurnata5 (0.041)7 (0.034)2 (-17%)6 (0.014)8 (0.012)2 (-14%)10 (0.014) Least Concern Choerades marginatus8 (0.066)16 (0.077)8 (17%)9 (0.021)23 (0.034)14 (62%)10 (0.014) Diclysmachus picipes11 (0.090)15 (0.072)4 (-20%)12 (0.028)25 (0.037)13 (32%)16 (0.022) Dioctria atricapilla13 (0.107)52 (0.251)39 (135%)29 (0.068)76 (0.111)47 (63%)69 (0.095) Dioctria hyalipennis28 (0.230)45 (0.217)17 (-6%)40 (0.093)72 (0.105)32 (13%)47 (0.065) Dioctria linearis6 (0.049)19 (0.092)13 (88%)11 (0.026)27 (0.040)16 (54%)18 (0.025) Dioctria oelandica8 (0.066)19 (0.092)11 (39%)9 (0.021)32 (0.047)23 (124%)10 (0.014) Dioctria rufipes7 (0.057)22 (0.106)15 (86%)9 (0.021)32 (0.047)22 (124%)10 (0.014) Dysmachus trigonus19 (0.156)51 (0.246)32 (58%)46 (0.107)93 (0.149)47 (39%)75 (0.103) Laphria flava3 (0.025)16 (0.077)13 (208%)33 (0.077)26 (0.038)-7 (-49%)66 (0.089) Lasiopogon cinctus8 (0.066)23 (0.111)15 (68%)25 (0.058)36 (0.053)11 (-9%)37 (0.051) Leptogaster cylindrica12 (0.098)30 (0.145)18 (48%)28 (0.065)67 (0.098)39 (51%)44 (0.061) Leptogaster guttiventris8 (0.066)16 (0.078)8 (18%)10 (0.023)28 (0.045)18 (96%)10 (0.014) Neoitamus cyanurus27 (0.221)44 (0.213)17 (-4%)58 (0.136)90 (0.132)32 (-3%)71 (0.098) Pamponerus germanicus7 (0.057)9 (0.043)2 (-25%)8 (0.019)20 (0.029)12 (53%)8 (0.011) Philonicus albiceps23 (0.189)26 (0.126)3 (-33%)51 (0.119)75 (0.110)24 (-8%)78 (0.107) Tolmerus atricapillus15 (0.123)33 (0.159)18 (29%)28 (0.065)53 (0.078)25 (20%)32 (0.044) Data Deficient Tolmerus cingulatus00000000

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Table 3. Danish Asilidae (Diptera). Comparison of collecting efforts per region for two time periods. See Methods section for abbreviations.

Successful collecting events

Change Regions

% 1920–1960 1961–2001

NWJ 53 15 -72

NEJ 23 143 522

WJ 38 58 53

EJ 65 176 170

SJ 81 14 -83

F 16 47 194

NWZ 8 25 212

NEZ 86 132 53

SZ 10 11 10

LFM 28 20 -29

B 15 37 147

but we doubt that there would be enough data for comparison. For each time period and species we tabulated the number of specimens, collecting events, and number of grids in which it was found.

When the data indicate that a species is becoming less abundant and its distribution is shrinking in the sample, this phenomenon can conceivably be due to lack of sampling and it is therefore impera- tive that differences in sampling intensity be taken into account. We are using three ap- proaches:

(1) For both time periods we counted for the entire asilid sample the number of UTMs with collecting events, the number of collecting events, and number of specimens collected. This provides an overall picture for sampling intensity during the two periods (Table 2). We furthermore determined the same values for each species sepa- rately and then divided them through the totals for the entire sample in order to obtain the proportion of specimens belonging to any particular species during the two time periods (Table 1). For exam- ple, Laphria flava was collected 33 times from 1920–1960 and 26 times thereafter. For the same time periods we have 429 and 683 collecting events for all Asilidae. The relative proportion of L. flava has thus dropped considerably from 7.7%

to 3.8% although the absolute numbers are rather similar.

It should be noted that when dividing the number of 10-km UTM grid and the number of collecting events of each species through the totals of Table 2, the sum of proportions in Table 1 becomes larger than 1. This is because in Table 1 the number of 10-km UTM grids and the number of collecting events were counted for each species, whereas in Table 2 no distinction was made between species. Since more than one species could be found within a single 10-km UTM grid and more than one species could be

collected at a single collecting event, the total sum of 10-km UTM grids and collecting events in Table 1 exceeds the numbers in Table 2. As a result, the sum of proportions is larger than 1.

This, however, is not a problem given that the relative proportions are used to calculate changes within a species and not between species.

(2) For the 11 Danish faunal regions we also compared the number of collecting events that have yielded Asilidae during the two periods.

This allows us to judge whether the disappear- ance of a species from a particular region might be due to reduced overall collecting. The 11 faunal regions are North West Jutland (NWJ), North East Jutland (NEJ), West Jutland (WJ), East Jutland (EJ), South Jutland (SJ), Funen (F), North West Zealand (NWZ), North East Zealand (NEZ), South Zealand (SZ), Lolland, Falster and Moen (LFM) and Bornholm (B).

(3) For threatened or Near Threatened species, we furthermore studied whether the grids in which they have been known to occur have been well-sampled after 1920.

RESULTS

Of the 4391 specimens included in our study, 4194 had sufficiently precise locality information to assign them to a 10 km UTM grid, while only 3424 specimens contained date information on the label. Of the specimens without date 463 were

Table 2. Danish Asilidae (Diptera). Summary of collecting efforts for two time periods.

1920–1960 1961–2001 No. 10-km UTM

grids with records 122 207

No. specimens collected 728 1195

No. collecting events 429 683

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Figs 29–59 and accompanied by information on distribution and abundance changes for each species during the two time periods (1920–1960, 1961–2001).

Quantitative analysis reveals that the data suf- fer from spatial and temporal collecting bias. The number of collecting events differs greatly between the different grids with some grids lacking any records (Fig. 28). Furthermore, collecting activity in the 11 Danish faunistic regions during the two time periods (1920–1960, 1961–2001) is not directly comparable (Table 2). For most regions collecting after 1960 increased. There are only three regions where collecting has de- creased. The most dramatic decrease is observed for South- and Northwest Jutland (Table 3). We therefore produced Table 1, which presents for each species the number of grids, number of collecting events, and number of collected specimens during the two time periods. The observed numbers are normalized by the corresponding numbers for the entire asilid sample and reveal for which species a decline has been observed.

According to the IUCN criteria, one species is listed as Data Deficient (DD): Tolmerus cin- gulatus; one species is listed as Regionally Ex- tinct (EX): Molobratia teutonus; five species are listed as Critically Endangered (CR): Antipalus varipes, Cyrtopogon lateralis, Machimus arthri- ticus, M. gonatistes, Neoitamus cothurnatus; two species are listed as Endangered (EN): Eutolmus rufibarbis, Laphria ephippium; three species are listed as Vulnerable (VU): Asilus crabronifor- mis, Leptarthrus brevirostris, Rhadiurgus variabilis; two species are listed as Near Threat- ened (NT): Choerades gilvus; Dioctria cothur- nata; and 16 species are listed as Least Concern (LC): Choerades marginatus, Laphria flava, Dioctria atricapilla, D. hyalipennis, D. linearis, D. oelandica, D. rufipes, Lasiopogon cinctus, Leptogaster cylindrica, L. guttiventris, Didys-

asterisk). The classification follows Petersen et al. (2001) except that Dioctria baumhaueri is considered a synonym of D. hyalipennis accord- ing to Geller-Grimm’s catalogue (http://www.

geller-grimm.de/catalog/species.htm).

Laphriinae

Andrenosoma atra (Linnaeus, 1758)*

Choerades fuliginosa (Panzer, 1798)*

Choerades gilvus (Linnaeus, 1758) Choerades ignea (Meigen, 1820)*

Choerades marginatus (Linnaeus, 1758) Choerades rufipes (Fallén, 1814)*

Laphria ephippium (Fabricius, 1781) Laphria flava (Linnaeus, 1761) Laphria gibbosa (Linnaeus, 1758)*

Stenopogoninae

Dioctria atricapilla Meigen, 1803 Dioctria cothurnata Meigen, 1820 Dioctria hyalipennis (Fabricius, 1794) Dioctria linearis (Fabricius, 1787) Dioctria oelandica (Linnaeus, 1758) Dioctria rufipes (De Geer, 1776) Molobratia teutonus (Linnaeus, 1767) Lasiopogon cinctus (Fabricius, 1781) Lasiopogon montanus Schiner, 1862*

Cyrtopogon lateralis (Fallén, 1814)

Cyrtopogon maculipennis (Macquart, 1834)*

Dasypogoninae

Dasypogon diadema (Fabricius, 1781)*

Leptarthrus brevirostris (Meigen, 1804) Leptarthrus vitripennis (Meigen, 1820)*

Leptogastrinae

Leptogaster cylindrica (De Geer, 1776) Leptogaster guttiventris Zetterstedt, 1842 Asilinae

Antipalus varipes (Meigen, 1820)

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Asilus crabroniformis Linnaeus, 1758 Didysmachus picipes (Meigen, 1820) Dysmachus bifurcus (Loew, 1848)*

Dysmachus trigonus (Meigen, 1804) Erax barbatus Scopoli, 1763*

Eutolmus rufibarbis (Meigen, 1820) Machimus arthriticus (Zeller, 1840) Machimus gonatistes (Zeller, 1840) Machimus rusticus (Meigen, 1820)*

Machimus setibarbis (Loew, 1849)*

Neoitamus cothurnatus (Meigen, 1820) Neoitamus cyanurus (Loew, 1849) Neoitamus socius (Loew, 1871)*

Pamponerus germanicus (Linnaeus, 1758) Philonicus albiceps (Meigen, 1820) Rhadiurgus variabilis (Zetterstedt, 1838) Tolmerus atricapillus (Fallén, 1814) Tolmerus cingulatus (Fabricius, 1781)

KEY TO THE DANISH ASILIDAE Figures illustrating the key are redrawn from the following sources: Figs. 1–5, 7–15, 18–27: Wein- berg & Bäckli (1995); Fig. 6: Geller-Grimm &

Smart (1998); Figs. 16–17: Lyneborg (1965).

1. Marginal cell r₁ open (Fig. 1a) ... 2 – Marginal cell r₁ closed (Fig. 1b) ... 17 2. Alula absent; pulvilli absent; abdomen elongated and slender; claws long and slender (Fig. 2a) Leptogaster ... 3

– Alula present; pulvilli present; abdomen not particularly elongated and slender; claws strong (Fig. 2b) ... 4 3. Hind femora with dark longitudinal line; apical quarter of hind tibia dark brown; tarsi dark; all abdominal tergites with brown lon- gitudinal dorsal line ... L. cylindrica – Hind femora with dark ring; hind tibiae and tarsi light brown; median abdominal tergites with brown transverse line at posterior mar- gin ... L. guttiventris 4. Spine at apex of fore tibia absent ... 5 – Spine at apex of fore tibia present (Fig. 3a, b) ... 14

Fig. 1. Wing, marginal cell r1. a: open; b: closed, Antipalus varipes.

Fig. 2. Claws. a: long and slender, Leptogaster sp; b: strong, Asilus sp.

Fig. 3. Fore tibial spine. a: small, e.g., Leptarthrus sp.; b:

thick, on a protuberance, e.g., Dasypogon sp.

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5. Facial gibbosity only slightly developed or indistinct; mystax confined to ventral part of face; antenna longer than height of eyes, inserted on a black, atomentose (shiny) protu- berance (Fig. 4) ... Dioctria ... 6 – Facial gibbosity distinct, broader than diam- eter of proboscis (Fig. 5); antenna shorter than height of eyes ... 11

6. Coxae yellow; abdominal tergites with yellow posterior margins, tergites 3–5 with additional yellow markings; scutum grey tomentose, only two narrow paramedial and two broader lateral stripes atomentose (shiny) ... D. linearis – Coxae dark; entire abdomen black; scutum mainly atomentose ... 7 7. All legs black or dark brown; basis of wings in males dark brown; mystax in males black, in females pale yellow ... D. atricapilla – Fore femora not black; basis of wings not darkened (wings entirely darkened in oelan- dica); mystax yellow ... 8 8. Only dorsal margin of anepisternum with grey tomentum ... D. cothurnata – Grey tomentum on dorsal, anterior and posterior margins of anepisternum (Fig. 6) ... 9 9. Supra-alar bristles mostly black; wings entirely dark brown; legs reddish-yellow, apex of tibiae and tarsi black ... D. oelandica – Supra-alar bristles reddish-yellow; wings not darkened; legs light to dark brown ... 10 10. Facial gibbosity in profile higher than length of pedicel; fore and mid legs reddish-yellow;

hind legs black with basis of femora and 1^st tarsomere reddish-yellow ... D. rufipes – Facial gibbosity in profile shorter than length of pedicel; fore and mid legs yellow; apex of tibia black ... D. hyalipennis

Fig. 4. Lateral view of head. Antenna inserted on a black shiny protuberance, Dioctria sp.

Fig. 5. Lateral view of head. With well-developed facial gibbosity, Pamponerus sp.

Fig. 6. Anepisternum. Tomentum (shaded) on upper and lateral margins, Dioctria sp.

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11. Dorsocentral bristles present; frons divergent towards vertex (Fig. 7); only lower part of facial gibbosity developed ... Lasiopogon ... 12 – Dorsocentral bristles absent; frons not divergent; entire face with well-developed facial gibbosity Cyrtopogon ... 13

12. Abdominal tergite 1 with yellow lateral marginal bristles; wings with black or dark veins;

hypopygium black (Fig. 8a) ... L. cinctus – Abdominal tergite 1 with at least one black lateral marginal bristle; wings with light brown veins; hypopygium reddish-brown (Fig. 8b) ... L. montanus 13. Legs black ... Cyrtopogon lateralis – Legs with yellow or red areas ...

... C. maculipennis 14. Postpedicel with three micro segments form- ing a down bending terminal style; fore tibial spine small and attached directly on tibia (Fig. 3a) ... Leptarthrus ... 15 – Postpedicel (third antennal segment) with one segmented terminal style, held erect; fore tibial spine thick and attached on a protuberance on tibia (Fig. 3b) ... 16 15. Face atomentose, shiny black; scutum with long hairs; female abdominal tergites with white grey tomentose corners; mystax in males black, in females yellow ...

... L. brevirostris – Face tomentose; scutum with short hairs anterior to transverse suture; abdominal tergites in both males and females with white tomentose corners; mystax in males white, in females yellow ... L. vitripennis 16. Third medial cell m₃ closed (Fig. 9a) ...

... Dasypogon diadema – Cell m₃ open (Fig. 9b) .. Molobratia teutonus

Fig. 7. Frontal view of head. Frons divergent toward vertex, Lasiopogon sp.

Fig. 8. Lateral view of hypopygium. a: Lasiopogon cinctus; b:

Lasiopogon montanus.

Fig. 9. Wing, third medial cell m3. a: closed, Dasypogon sp.;

b: open, Molobratia sp.

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– Postpedicel with a thin, long style (Fig. 10) ...

... 26 18. Postpedicel elongated; proboscis more or less laterally compressed ... 19 – Postpedicel short and thick; proboscis more or less dorso-ventrally compressed ...

... Andrenosoma atra 19. Apical tip of hind tibia ventrally with a thick, short hairy brush (Fig. 11) Choerades ... 20 – Ventral side of hind tibia without hairy brush (not as in Fig. 11); hind tibia in males with apical spine ventrally; hind tibia in females with long hairs ... Laphria ... 24 20. Legs red; tarsi more or less black ... C. rufipes – Legs black ... 21 21. Abdominal tergites entirely black; scape 3–4 times as long as pedicel ... 22 – Abdominal tergites black with yellowish-red markings; scape two times as long as pedicel ... 23 22. Postpronotal lobe (shoulders) grey tomentose; abdomen with short, black or yellow hairs; posterior margin of abdominal tergites with long, yellow hairs laterally ...

... C. marginatus – Postpronotal lobe atomentose; abdomen with yellowish-white hairs, especially long

cept tergite 1, medially with reddish-yellow hairs ... C. ignea 24. Abdominal tergites with mostly black hairs, laterally few white hairs Laphria ephippium – Abdominal tergites 4–6 with yellow hairs . 25 25. Abdominal tergites 1–3 with black hairs, tergites 4–6 with yellow hairs; hairs on scu- tum short ... L. gibbosa – All abdominal tergites with yellow hairs;

hairs on scutum posterior to transverse suture long ... L. flava 26. Postocular bristles long and sharply bent forward (Fig. 12); abdominal tergite 7 shiny black or brown; mystax with white bristles ventrally and black bristles dorsally ...

Neoitamus ... 27 – Postocular bristles erect or only slightly bent forwards ... 29 27. Fore tibia with yellow bristles ventrally; abdomen shiny black from tergite 5 on ...

... N. cothurnatus – Fore tibia with black or reddish-brown bristles ventrally ... 28

Fig 11. Tibia. Distal tip with short hairy brush, Choerades sp.

Fig. 12. Lateral view of head. Postocular bristles sharply bent forward, Neoitamus sp.

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187

28. Hind legs with black bristles; hypopygium quadrangular and broader apically than basally, with long hairs ventrally (Fig. 13a) ....

... N. socius – Hind legs with mostly black bristles (few yellow); abdominal tergites 1–5 tomentose, apical tergites atomentose, shiny; hypopygium narrower apically than basally, only short bristles ventrally (Fig. 13b) ...

... N. cyanurus 29. Postocular bristles short and thick, mostly yellow; female cerci with four spines each (Fig. 14a); hypopygium shiny black with white hairs laterally and black hairs dorsally (Fig. 14b) ... Philonicus albiceps

– Postocular bristles not particularly thickened, yellow ... 30 30. Postpedicel elongated, narrower than pedicel; apical three abdominal tergites short and laterally compressed (Fig. 15) ...

... Erax barbatus – Postpedicel thickened; abdominal tergites with general shape ... 31 31. Face atomentose, shiny black; ovipositor as in Fig. 16a; hypopygium as in Fig. 16b ....

... Rhadiurgus variabilis – Face tomentose ... 32 32. Scape yellow; wings yellowish with brown areas on posterior margin; abdominal tergites 4–7 yellow ... Asilus crabroniformis – Scape black or brown; abdominal tergites black ... 33

Fig. 14. Lateral view of terminalia of Philonicus albiceps. a:

ovipositor; b: hypopygium.

Fig. 13. Lateral view of hypopygium. a: Neoitamus socius; b:

Neoitamus cyanurus.

Fig. 15. Lateral view of head of Erax barbatus.

Fig. 16. Lateral view of terminalia of Rhadiurgus variabilis.

a: ovipositor; b: hypopygium.

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33. Posterior margin of abdominal tergites without lateral marginal bristles; basis of wings white; ovipositor as in Fig. 17a, hypopygium as in Fig. 17b ... Pamponerus germanicus – Posterior margin of abdominal tergites with lateral marginal bristles ... 34 34. Acrostichal bristles long; dorsocentral bristles reaching anterior margin of scutum; cerci of female enclosed (Fig. 18a) ... 35 – Acrostichal bristles anterior to transverse suture short; dorsocentral bristles do not reach anterior margin of scutum; cerci of female free (Fig. 18b) (except Eutolmus) ...

Machimus-complex ... 37 35. Scutellum with 6–10 yellow bristles;

acrostichal bristles thick; ovipositor as in Fig.

19 ... Dysmachus trigonus – Scutellum with 2–4 mostly yellow bristles . ... 36

36. Tibiae black, sometimes apically red; ovipositor as in Fig. 20a; hypopygium as in Fig.

20b ... Didysmachus picipes – Tibiae red; ovipositor as in Fig. 21a; hypo- pygium as in Fig. 21b ... Dysmachus bifurcus

Fig. 17. Lateral view of terminalia of Pamponerus ger- manicus. a: ovipositor; b: hypopygium.

Fig. 18. Lateral view of ovipositor. a: cerci enclosed, Dysma- chus sp.; b: free cerci, Machimus rusticus.

Fig. 20. Lateral view of terminalia of Didysmachus picipes. a:

Fig. 21. Lateral view of terminalia of Dysmachus bifurcus. a:

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189

37. Males ... 38 – Females ... 45 38. Abdominal sternite 8 with posterior projection (e.g., Fig. 22a) ... 39 – Abdominal sternite 8 with straight posterior margin ... 43 39. Projection on abdominal sternite 8 bifurcated (Fig. 22a); hypopygium black (Fig. 22b) ...

... Tolmerus atricapillus – Projection on abdominal sternite 8 simple .40 40. Legs entirely black ... 41 – Basis of tibiae red ... 42 41. Projection on abdominal sternite 8 short, triangular; legs with black bristles, and black and yellowish-white hairs; mystax with long black bristles medially, shorter white bristles ventrally; hypopygium as in Fig. 23a ...

... Machimus setibarbis – Projection on sternite 8 long and slender, triangular, with black and yellow hairs; legs with black bristles and yellow hairs; mystax with short black bristles dorsally and long yellow bristles medially and ventrally; hypo- pygium as in Fig. 23b ... Eutolmus rufibarbis 42. Legs with black bristles; scutellum with 6–7 yellow and black bristles; fore femora without bristles ventrally; hypopygium as in Fig.

24a ... Machimus gonatistes

– Legs with mostly yellow bristles; scutellum with 4–8 yellow bristles .. Machimus rusticus 43. Femora black with red apical and ventral markings; tibiae red with a more or less complete dark brown ring medially; hypopygium as in Fig. 24b ... Tolmerus cingulatus – Femora black ... 44

Fig. 24. Lateral view of hypopygium. a: Machimus gona- tistes; b: Tolmerus cingulatus.

Fig. 22. Tolmerus atricapillus. a: bifurcated projection on sternite 8 in ventral view; b: hypopygium in lateral view.

Fig. 23. Lateral view of hypopygium. a: Machimus setibarbis;

b: Eutolmus rufibarbis.

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44. 1^st tarsomere of fore tarsi shorter than the two following tarsomeres; abdominal sternites with yellow hairs only; hypopygium shiny black (Fig. 25a) ... Antipalus varipes – 1^st tarsomere of fore tarsi longer than the two following tarsomeres; abdominal sternites 2–

4 with strong yellow bristles and hairs; hypo- pygium as in Fig. 25b .. Machimus arthriticus 45. Cerci enclosed (Fig. 26); mystax with black bristles dorsally and white bristles ventrally . ... Eutolmus rufibarbis – Cerci free ... 46

46. Ovipositor broader than long (Fig. 27); 1^st tarsomere of fore tarsi shorter than the two following tarsomeres combined; mystax black and white ... Antipalus varipes – Ovipositor longer than wide; 1^st tarsomere of fore tarsi longer or equal the length of the two following tarsomeres combined ... 47 47. Abdominal sternites 2–4 with long yellow bristles and hairs; legs with mostly yellow bristles ... Machimus arthriticus – Abdominal sternites 2–4 without bristles, only hairs present; legs with mostly black bristles ... 48 48. Legs black with black bristles, and black and yellowish-white hairs; mystax with long black bristles medially and shorter white bristles ventrally ... Machimus setibarbis – Legs not entirely black ... 49 49. Femora black ... 50 – Femora with red apical and ventral markings ... 51 50. Legs with black bristles; fore femora without bristles on ventral side; scutellum with 6 yellow and black bristles ...

... Machimus gonatistes – Legs with mostly yellow bristles; scutellum with 4–8 yellow bristles ...

... Machimus rusticus 51. Femora black with red apical and ventral markings; tibiae red with a more or less complete dark brown ring medially ...

... Tolmerus cingulatus – Fore femora either yellow or black, mostly black or dark brown in dorsal half, light brown in ventral half or only dark ventrally;

tibiae reddish-brown .. Tolmerus atricapillus

Fig. 26. Lateral view of ovipositor of Eutolmus rufibarbis with cerci enclosed.

Fig. 27. Lateral view of ovipositor of Antipalus varipes.

Fig. 25. Lateral view of hypopygium. a: Antipalus varipes; b:

Machimus arthriticus.

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191

Explanation of distribution maps

Figs. 29–58. Distribution maps, species name and number as below, at upper left of each map. – Figs 29–38, 40–57. Relative (y-axis), and absolute abundance (numbers above columns) of the named species, based on specimens with label data. For Fig. 39 (Molobratia teutonus) and Fig.

58 (Tolmerus cingulatus) there are no post-1920 records and therefore no histogram displaying the abundance in the two time periods.

Fig. 28. Danish Asilidae (Diptera). Distribution map indicating the number of collecting events for the different 20-km UTM grids.

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DISTRIBUTIONAL INFORMATION ON THE SPECIES

LAPHRIINAE

1. Choerades gilvus (Linnaeus, 1758)

Minimum flying period: 20 May–08 September (Germany: mid-May–mid-October; Wolff 2002).

– Collecting period: 1824–2001. – Number of specimens and collecting events: 201, 103. – Distribution: This species is present in all regions, but found mostly along the coasts (Fig. 29). – Red List category: NT.

Fig. 29

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193

Fig. 30

2. Choerades marginatus (Linnaeus, 1758) Minimum flying period: 25 May–12 September (Germany: mid-May–September; Wolff 2002). – Collecting period: 1821–2001. – Number of

specimens and collecting events: 168, 102. – Distribution: This species is not found in North- and West Jutland (Fig. 30). – Red List category:

LC.

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3. Laphria ephippium (Fabricius, 1781) Minimum flying period: 20 May–26 July (Ger- many: mid-May–August; Wolff 2002). – Collect- ing period: 1873–1990. – Number of specimens and collecting events: 86, 50. – Distribution: The majority of collecting sites are found east of a

midline passing through Jutland. The time of sampling for most specimens is before 1960.

Specimens are also found in a few localities in Northeast Zealand (Fig. 31). – Red List category:

NT.

Fig. 31

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195

4. Laphria flava (Linnaeus, 1761)

Minimum flying period: 16 May–17 August (Germany: mid-April–mid-September; Wolff 2002). – Collecting period: 1935–1999. – Number of specimens and collecting events: 101,

59. – Distribution: Specimens are found in mid and southern Jutland and in Northeast Zealand.

Except for a few sites close to the German border all collecting for this species has been done after 1960 (Fig. 32). – Red List category: LC.

Fig. 32

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STENOPOGONINAE

5. Dioctria atricapilla Meigen, 1804

Minimum flying period: 02 May–30 July (Ger- many: May–August; Wolff 2002). – Collecting

period: 1818–2001. – Number of specimens and collecting events: 338, 179. – Distribution: A very abundant species found in all regions (Fig.

33). – Red List category: LC.

Fig. 33

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197

6. Dioctria cothurnata Meigen, 1820

Minimum flying period: 12 June–30 August (Germany: late May–mid-September; Wolff 2002). – Collecting period: 1820–2001. – Number of specimens and collecting events: 96, 48. – Distribution: Most specimens of this species

are found in Jutland, where all time periods are represented (except for West Jutland). No specimens have been found on Funen and Bornholm and there are only few and old records for Zealand (Fig. 34) – Red List category: NT.

Fig. 34

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7. Dioctria hyalipennis (Fabricius, 1794) Minimum flying period: 17 March–23 August (Germany: May–mid-September; Wolff 2002). – Collecting period: 1820–2001. – Number of

specimens and collecting events: 378, 248. – Distribution: The species is common, but most abundant in East Jutland, Funen and Zealand (Fig. 35). – Red List category: LC.

Fig. 35

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199

8. Dioctria linearis (Fabricius, 1787)

Minimum flying period: 24 March–16 August (Germany: mid-May–mid-August; Wolff 2002).

– Collecting period: 1873–2001. – Number of specimens and collecting events: 113, 72. Distri-

bution: The species is restricted to Funen, Zea- land and Lolland, Falster and Moen except for a few sites on the east coast of Jutland (Fig. 36). – Red List category: LC.

Fig. 36

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9. Dioctria oelandica (Linnaeus, 1758) Minimum flying period: 14 May–10 October (Germany: mid-March–mid-August; Wolff 2002). – Collecting period: 1872–2001. – Number of specimens and collecting events: 154,

101. – Distribution: Most records come from central and West Jutland, Zealand and Bornholm.

Recent specimens are mostly from Bornholm (Fig. 37). – Red List category: LC.

Fig. 37

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201

10. Dioctria rufipes (De Geer, 1776)

Minimum flying period: 13 May–15 July (Ger- many: May–end-August; Wolff 2002). – Collect- ing period: 1820–1998. – Number of specimens and collecting events: 167, 99. – Distribution:

The distribution of this species mostly covers Zealand and a few sites on Bornholm and Funen.

In Jutland it is mostly found in the mid-eastern parts and there are only few records in the north and west (Fig. 38). – Red List category: LC.

Fig. 38

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11. Molobratia teutonus (Linnaeus, 1767) Minimum flying period: Unknown (Germany:

mid-May–mid-July; Wolff 2002). Only two specimens have been recorded and neither label car-

ried a date. – Number of specimens and collecting events: 2, 2. – Distribution: Both specimens were found in North Zealand before 1910 (Fig. 39). – Red List category: EX.

Fig. 39

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203

12. Lasiopogon cinctus (Fabricius, 1781) Minimum flying period: 19 April–14 July (Ger- many: April–July; Wolff 2002). – Collecting period: 1819–2001. – Number of specimens and collecting events: 243, 115. – Distribution: Spec-

imens found in Jutland and in Zealand represent all periods. On Bornholm specimens have only been found after 1960 (Fig. 40). – Red List category: LC.

Fig. 40

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13. Cyrtopogon lateralis (Fallén, 1814) Minimum flying period: based on 3 collecting events: 13 June–24 June(Germany: May-mid–

August; Wolff 2002). – Collecting period: 1905–

1977. – Number of specimens and collecting

events: 3, 3. – Distribution: Only three specimens have been collected and all have been taken in Northeast Zealand (Fig. 41). – Red List category:

CR.

Fig 41

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205

DASYPOGONINAE

14. Leptarthrus brevirostris (Meigen, 1804) Minimum flying period: 24 March–13 July (Ger- many: mid-May–mid-August; Wolff 2002). – Collecting period: 1872–1987. – Number of specimens and collecting events: 84, 27. – Distri-

bution: This species has only been found on Zea- land, Lolland and Bornholm. On Lolland and Bornholm the specimens were collected after 1960, whereas on Zealand most sites are only represented by specimens collected before 1910 (Fig. 42). – Red List category: VU.

Fig. 42

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LEPTOGASTRINAE

15. Leptogaster cylindrica (De Geer, 1776) Minimum flying period: 14 May–29 August (Germany: mid-May–mid-September; Wolff 2002). – Collecting period: 1871–2001. –

Number of specimens and collecting events:

286, 184. – Distribution: Specimens are found throughout Denmark, representing all time periods (except North Jutland with mostly recent records) (Fig. 43). – Red List category: LC.

Fig. 43

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207

16. Leptogaster guttiventris Zetterstedt, 1842 Minimum flying period: 05 June–05 September (Germany: mid-May–end-September; Wolff 2002). – Collecting period: 1819–1993. – Number of specimens and collecting events: 91,

67. – Distribution: This species is almost absent in North- and West Jutland. In Northeastern Zea- land it has been collected in all time periods, whereas there are only older records for the rest of Zealand (Fig. 44). – Red List category: LC.

Fig. 44

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ASILINAE

17. Antipalus varipes (Meigen, 1820)

Minimum flying period: 03 June–15 August (Germany: mid-June–mid-September; Wolff 2002). – Collecting period: 1904–1959. –

Number of specimens and collecting events: 41, 29. – Distribution: All specimens were collected before 1960 and with the exception of an old one from North Jutland all come from North Zealand (Fig. 45). – Red List category: CR.

Fig. 45

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209

18. Asilus crabroniformis Linnaeus, 1758 Minimum flying period: 21 May–27 September (Germany: June–-October; Wolff 2002). – Col- lecting period: 1821–1997. – Number of specimens and collecting events: 188, 117. – Distribu- tion: With the exception of North- and West

Jutland, this species is widely distributed in Den- mark although for the majority of sites it has not been found after 1960. Newer specimens are mostly found in central and North Jutland (Fig.

46). – Red List category: VU.

Fig. 46

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19. Didysmachus picipes (Meigen, 1820) Minimum flying period: 17 May–08September (Germany: mid-May–mid-August; Wolff 2002).

– Collecting period: 1821–1984. – Number of specimens and collecting events: 193, 125. –

Distribution: The distribution of this species re- sembles that of Dioctria rufipes (Fig. 39) except for a lack of records from Bornholm (Fig. 47). – Red List category: LC.

Fig. 47

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211

20. Dysmachus trigonus (Meigen, 1804) Minimum flying period: 04 May–03 September (Germany: May–August; Wolff 2002). – Collect- ing period: 1881–2001. – Number of specimens and collecting events: 359, 205. – Distribution: In

Jutland and Funen this species is widely distributed and there are records for all time periods, whereas records on Zealand and Bornholm are much more sparse (Fig. 48). – Red List category:

LC.

Fig. 48

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21. Eutolmus rufibarbis (Meigen, 1820) Minimum flying period: 02 July–28 August (Ger- many: mid-June–August; Wolff 2002). – Collect- ing period: 1881–1989. – Number of specimens

and collecting events: 52, 24. – Distribution:

Specimens are found in isolated sites in Jutland, Funen, Zealand and Bornholm, but most are from before 1910 (Fig. 49). – Red List category: EN.

Fig. 49

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213

22. Machimus arthriticus (Zeller, 1840) Minimum flying period: 20 June–24 July (Ger- many: June–mid-August; Wolff 2002). – Collect- ing period: 1883–1974. – Number of specimens and collecting events: 22, 14. – Distribution: This

species is largely restricted to mid- and southern Jutland with a few exceptions from Funen and Bornholm. The only specimen found after 1960 was collected on Djursland (Fig. 50). – Red List category: CR.

Fig. 50

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23. Machimus gonatistes (Zeller, 1840) Minimum flying period: 24 June–19 July (Ger- many: mid-July–August; Wolff 2002). – Collect- ing period: 1934–2001. – Number of specimens

and collecting events: 17, 6. – Distribution: This species has only been collected on Anholt (Fig.

51). – Red List category: CR.

Fig. 51

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215

24. Neoitamus cothurnatus (Meigen, 1820) Minimum flying period: Based on few collecting events: 07 June–21 July (Germany: mid-May–

mid-July; Wolff 2002). – Collecting period:

1883–1964. – Number of specimens and collect-

ing events: 10, 7. – Distribution: All specimens were either taken on Bornholm (all periods) or Zealand, where the species has not been collected since 1914 (Fig. 52). – Red List category: CR.

Fig.52

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25. Neoitamus cyanurus (Loew, 1849)

Minimum flying period: 14 May–08 September (Germany: mid-May–mid-September; Wolff 2002). – Collecting period: 1825–2001. – Number of specimens and collecting events: 418, 270. – Distribution: This species is abundant in all

regions and time periods with the exception of West Jutland, from which it is unknown. After 1960 it is particularly commonly collected on Funen and Zealand (Fig. 53). – Red List category:

LC.

Fig. 53

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217

26. Pamponerus germanicus (Linnaeus, 1758) Minimum flying period: 18 May–12 August (Germany: April–mid-August; Wolff 2002). – Collecting period: 1820–2001. – Number of specimens and collecting events: 145, 77. – Dis-

tribution: In Jutland the species is restricted to the northeastern parts, but it is also found on Zealand, Lolland, Falster and Møn. After 1960 it was only found in North Zealand (Fig. 54). – Red List category: LC.

Fig. 54

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27. Philonicus albiceps (Meigen, 1820) Minimum flying period: 30 May–14 September (Germany: mid-May–mid-October; Wolff 2002).

– Collecting period: 1821–2001. – Number of specimens and collecting events: 331, 195. – Distribution: This species is abundant in all re-

gions, except for South and East Zealand, but sampling has mostly occurred before 1960. Most recent records come from Funen, Bornholm and Northwest Zealand (Fig. 55). – Red List category:

LC.

Fig. 55

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219

28. Rhadiurgus variabilis (Zetterstedt, 1838) Minimum flying period: 10 June –23 August (Germany: mid-May–mid-September; Wolff 2002). – Collecting period: 1907–1979. – Number of specimens and collecting events: 29,

21. – Distribution: This species has only been recorded from isolated sites in Jutland, on Funen and on Zealand (Fig. 56). – Red List category:

VU.

Fig. 56

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29. Tolmerus atricapillus (Fallén, 1814) Minimum flying period: 28 May–20 October (Germany: mid-June–mid-November; Wolff 2002). – Collecting period: 1824–2001. – Number of specimens and collecting events: 321, 191. – Distribution: This species is represented in

all periods on Funen, Zealand and Bornholm.

However, no specimens have ever been caught in Northwest Jutland, and most sites in East Jutland are only represented by specimens collected before 1960 (Fig. 57). – Red List category: LC.

Fig. 57

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221

30. Tolmerus cingulatus (Fabricius, 1781) Minimum flying period: 25 July–13 August (Ger- many: June–September; Wolff 2002). – Collect- ing period: 1819–1912. – Number of specimens and collecting events: 6, 4. – Distribution: This

species has not been collected in Denmark since 1912. Prior to 1912 it was found on Bornholm, North Zealand and Lolland (Fig. 58). – Red List category: DD.

Fig. 58

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(Appendix 1). Furthermore, Asilidae can be identified as such under field conditions so that tar- geted collecting by nonspecialists is feasible. The robber flies are thus one of the few Diptera groups that could be promoted for the kind of non- specialist collecting that is required for covering the large area of a country like Denmark. Further- more, robber flies are not only easily recognized and attractive, but at the same time vulnerable to habitat disturbance. Being relatively large and predaceous as larvae and adults, populations tend to be small. Moreover, the adults of many species favor warm and dry habitats like dry pastures, heathlands, and dune landscapes. These habitats are either quickly disappearing from many temperate countries and/or are subject to much disturbance. It is thus not surprising that a decline in asilid populations has been observed in many European countries (e.g., van Aartsen & van der Goot 1981, Verlinden 1982).

The use of specimen databases from collections has recently received much attention (e.g., Fagan & Kareiva 1997, Kress et al. 1998, León- Cortés et al. 1998, Funk et al. 1999, Soberón et al.

2000). They contain the “most comprehensive, reliable source of knowledge” (Ponder et al.

2001) about the distribution of invertebrate groups and the data are of great value in biodiversity and conservation biology studies.

However, the information should not be used uncritically. As Ponder et al. (2001) aptly summa- rized “shortcomings of the data include the ad- hoc nature of the collections, presence-only data, biased sampling, and large collecting gaps in time and space...” The same problems plague our data and they can thus mostly serve as a baseline for future work. A more complete picture of the species diversity and ranges will only emerge after additional and systematic collecting covering poorly sampled regions (see Smith 2000).

However, studies like the one presented here will

varying number of collecting events across the different 20-km grid cells in Denmark (Fig. 28).

Normally one would attempt to correct for uneven sampling and some techniques have been suggested (e.g., Fagan & Kareira 1997, Ponder et al. 2001). However, none can be used here and the two main problems for our data remain non- standardized collecting and the fact that the number of unsuccessful collecting attempts in the various grids is unknown. The latter is particularly damaging, because the uneven distribution of successful collecting events documented in Fig. 28 can be equally well explained by either the uneven sampling, uneven abundance of Asilidae in the different grids, or a combination of both.

However, it appears likely that uneven sampling is particularly important.

(1) There are relatively few collecting events in large regions such as Northwest- and South Zealand, Lolland, Falster and Møn, and South Jutland (Table 3) and it is inconceivable that these regions are genuinely as species-poor as our sample suggests. It is more likely that they have simply been poorly collected. It is interesting that the same areas are also poorly sampled for the focal taxon of the only other atlas study of Danish Diptera, the Syrphidae (Torp 1994).

(2) Further evidence for unequal sampling comes from the regional bias created by important collectors. A typical case is J. G. Worm- Hansen (Tuxen 1961), who, between 1940 and 1959, collected 268 specimens (6% of our sample) thus contributing 130 collecting events to our data set (7%). Of these collecting events, 89 (68%) took place in his two favorite UTM grids (MG92: 62 events; MJ72: 27 events), which have since only been resampled 16 times. A similar bias was created by the extensive sampling scheme on Thy (UTM MJ72) undertaken by the Entomological Department of the Copenhagen Museum between 1953 and 1961 (Tuxen 1961–