Revision of How to tell if its a Lonchaeid from Tue, 2021-04-20 18:54

In simple terms – how to tell a Lonchaeid
This is a simple guide to the family developed to help with some common mistakes made by contributors of photos to to Dipterainfo and iNaturalist.

Quick checlist

Lonchaeids are  hairy acalyptrate flies – that's without a large lower calyptere that covers the halter!  with a body length oif 3–6 mm. They have broad wings, realtively large head and eyes , a broad thorax and a broad wide abdomen. The body colour is usually shiny blue-black except in genera Lamprolonchaea & Fulgenta where its metallic blue-green.  The wing is clear, only occasionally light brorown or with apical darkening, but never patterned. Halteres always black.

HEAD:  eyes large,  bare or occasionally hairy but never touching on top of head as in some other families. The frons is without without lateral setae - so the only strong setae are on the top of the head with none in the area between between the ocelli and the antennae -  ; face broad usually without strong facial ridge or antennal grooves. Antennae with first flagellomere of varying length, mainly black, but often orange-brown basally and / or ventrally; pedicel and scape usually dark. arista bare, pubescent or plumose.

THORAX:  with the top (mesonotum) rather strongly arched, slightly dusted  to highly polished; without a complete transverse suture, covered in fairly dense setulae, almost without setae as the dorsocentral and acrostichal setae both reduced to1-2 pairs on rear of mesonotum. anepisternum with a row of setae along posterior margin. Scutellum with 4 marginal setae otherwise bare or hairy; katepisternum with 1–2 strong dorsocentral setae and numerous setulae..

WING:  Broad -  costa (C) extended to vein M1, constricted, but not completely broken at position of humeral and subcostal breaks; Costal cell noticeably broad often causing the costa to bulge to accomodate it. Veins R 4=5 and M1 almost parallell. Vein Sc complete and free from vein R1; pterostigmal section (between insertions of veins Sc and R1), short to long; cells bm and dm separated; cell cup present; A1 continued to, or near to, wing margin as a fold or not; apical section of vein CuA1 shorter than crossvein dm-cu.  upper calypter well-developed, haltere invariably entirely blackish.

Legs stout, coxae, femora, and tibiae always blackish; tarsi often with basal tarsomeres yellowish; femora rather swollen, with numerous setae and setulae; tibiae without setae apart from at extreme apex.

Confusion with other similar families
Lonchaeidae superficially resemble some small Muscidae but as well as not having calypteres Lonchaeidae are separable by the absence of a complete transverse suture on the mesonotum and other characters such as having more setae on the mesonotum and legs.

Lauxanidae – Lonchaeids are often confused with the black, shiny species of Lauxanidae especially those in the genera Calliopum , Lauxania , Minettia  and Xenochaetina   BUT Lauxanids have 2 pairs of rlateral setae on the head  (black arrow) and  white halteres (yellow arrow) and often entirely or largely orange antennae . The eyes are also more widely separated on the frons and there is a dorsocentral seta on the anterior half of the toracic dorsum

             

Agromyzidae, lonchaeids differ in having a longer cell dm (shorter than distal section of vein M in Agromyzidae) and usually strong lateral setae on the frons. Female abdomen with conspicuously dark
and hard conical oviscape protruding from tip of abdomen -( this is usually fully hidden in Lonchaeidae, Anthomyiidae do not have a darkened costal section on the wing between Sc and R1, they have strong setae on hind tibia, almost always including two or more posterodorsals and they almost always have distinct vibrissae on the genae. A general caution should be taken towards certain dark Agromyzidae, with dark halteres. 

The metallic blue-green species in the genus Lamprolonchaea can resemble members of several other acalyptrate families, but the black halter and lack of setae on the tibiae are useful diagnostic features.

Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith