Bibio lanigerus Meigen, 1818

Bibio lanigerus Meigen, 1818 View in CoL

( Figs. 1–2 View FIGS )

Material Examined. USA: Massachusetts: Middlesex Co., Waltham, Brandeis University , 42.366°, -71.264°, 25 April 2023, J. Forrester, E. Dankowicz, 7 males, 2 females ( SFC), 8 specimens in EtOH ( MCZC ENT:952161); same except 42.3695°, -71.2535°, 26 April 2023, 15 males ( SFC); same except 42.336°, -71.261°, 3 May 2018, E. Dankowicz, 1 male ( MCZC ENT:803976); Suffolk Co., Boston, Forest Hills , 28 May 1926, George Salt, 1 male ( MCZC ENT:803977); same except 30 May 1927, collector unknown, 1 male ( MCZC ENT:803978); FRANCE: Gard , ca. 44°3', 3°26', La Rouvière, ca. 1.5 km SW, ~ 900 m, 9 April 1992, J.P. Haenni, st.1, 1male ( SFC); GERMANY: Saxony: Oetzsch , 3 May 1894, M. P. Riedel, 1 male ( MCZC ENT:803968); Thuringia: Pössneck, M. P. Riedel, 1 male ( MCZC ENT:803969); North Rhine-Westphalia: Uerdingen, M. P. Riedel, 2 males ( MCZC ENT:803970, 803971); Berlin, collector unknown, 2 males, 2 females ( MCZC ENT:803972, 803973, 803974, 803975).

Diagnosis. In the Nearctic region males ( Figs. 1–2 View FIGS ) can be distinguished by the following combination of characters: Legs bicolored (femora dark brown to black, tibiae lighter in color; orange to orange-brown), posterior wing veins pigmented, hind basitarsus slightly swollen, sausage-shaped, ca. 3–3.5x as long as wide and about 1/2 the width of the dilated apex of the hind tibia, fore tibial spur less than 1/2 length of spine, r-m subequal to distinctly longer than the base of Rs, antennal flagellum 7-segmented. This is a medium-sized (wing length about 4.5–5.5 mm) spring-flying species. In the eastern Nearctic region males can usually be quickly recognized by the combination of the bicolored hind legs (strongly contrasting dark femur and pale tibia) and posterior wing veins pigmented, though non-average specimens of some other species may also fit here.

Comments. Bibio lanigerus Meigen is widespread in Europe ( Krivosheina 1986). Material collected around Boston, Massachusetts dating back to 1926 was determined to be this species and compared with European specimens ( France & Germany) for confirmation. Over 300 photographic records (iNaturalist.com & BugGuide.Net) from between 2009 and 2023 were also confirmed to be B. lanigerus by ED and represent localities in Manhattan and western Long Island, New York; Connecticut; Rhode Island; eastern Massachusetts; southeastern New Hampshire; and southern Maine, USA. B. lanigerus appears to be an introduced species that has been slowly spreading from eastern Massachusetts.

Males of B. lanigerus are probably most similar to the western species B. sericatus Hardy , but can be distinguished by the more contrasting hind femur and tibia (black and yellow respectively verses black/dark brown and brown with rufous tint), thinner hind tibial spurs (flatter and more spatulate in B. sericatus ) and more apically dilated hind tibia (tibial apex about 2x the width of the basitarsus (see Duda 1930, Textfig. 26) versus only slightly broader than the basitarsus in B. sericatus ). Males of B. lanigerus key to couplet 47 ( B. nigrifemoratus Hardy and B. cognatus Hardy ) in Hardy (1945), but these are both western species with which it is unlikely to be confused; the former has been synonymized with B. atripilosus James ( Fitzgerald 1997b) and has very distinctive male terminalia ( Hardy1961: 185, Fig. 6c View FIG ) and males of B. cognatus have only 3–4 antennal flagellomeres rather than seven in B. lanigerus ( Hardy 1945, 1961). Males also do not key easily beyond couplet 4 in Hardy (1958; Insects of Connecticut) as the hind basitarsus is only slightly swollen rather than “distinctly enlarged” or “slender.” Females will key to B. fluginatus Hardy in Hardy (1945), but can be distinguished by the longer antennal flagellum; 7-segmented in B. lanigerus and 5-segmented in B. fluginatus .

Several keys are available to distinguish B. lanigerus from other European species (e.g. Duda 1930, Freeman & Lane 1985, Skartveit 1995), but it is noteworthy that there has been some confusion between this species and B. hybridus Haliday which was treated as a distinct species by Freeman & Lane (1985) based on a difference in pile color. Pile color can be extremely variable in Bibio species ( Fitzgerald & Skartveit 1997) and is not sufficient evidence by itself for distinguishing a separate species; B. hybridus was treated as synonym of B. lanigerus by Krivosheina (1986).

Biology. B. lanigerus differs behaviorally from other Bibio in the USA and Canada that have been observed because males usually perch with the wings spread horizontally out from the body (rather than folded over abdomen) when at rest ( Fig. 1 View FIGS ). This has not been noted for the other 18 species of Bibio in the USA and Canada that are represented by a considerable number of confirmed photographic records on iNaturalist.org.

Jack Forrester (one of the collectors of the specimens studied here) describes their behavior on multiple occasions as: "hiding presumably under dead leaves when sun is blocked and then suddenly emerging en masse once it comes out again." This behavior is typical for what has been observed for numerous species of Bibio in the western USA. Timing of Massachusetts records mirrors the known spring-emergence of this species in Europe (e.g. April–May flight period in Scotland; Skartveit et al. 2013).