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 check
Body - entirelly blue black / metallic blue green ✔
Head - Frons - vertical setae absent ✔
Eyes - NOT touching on top of head ✔
Thorax - Pro-thoracic suture absent ✔
Wing - Costal cell bulging forward ✔
Apical section of CuA1 shorter than dm-cu ✔
Costa NOT fully broken ✔
Legs - Femora and tibiae black ✔
All tibiae without setae on shaft ✔
Haltere black ✔
Female with very long ovipositor ✔
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 broad wide abdomen. The body colour is 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 are most commonly mistaken for some Lauxanidae and Agromyzidae - see below - they also resemble some small black 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.
Muscidae - several small shiny black Muscid flies of the genus Hydrotea can be mistaken for Lonchaeidae, as well as numerous other differences they have large lower calypteres which in photos are often obscured under the wing - but the eyes never touch on the frons like this in Lonchaeidae and the abdomen is usually rather narrow and pointed There is always a distinct pro-thoracic suture
photo sixtoalejandroanguloalpire photo Thomas Job
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 lateral setae on the head (black arrow) and usually 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 thoracic dorsum
Agromyzidae, As well as strong lateral setae on the frons and, apart from in a few tropical species, with pale halteres Agromyzidae have the apical sectionof vein CU A1 much longer than crossvein dm-cu. (red arrow) ,They 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. Female abdomen with conspicuously dark and hard conical oviscape protruding from tip of abdomen (blue arrow below) this is usually fully hidden in Lonchaeidae
photo Janet Graham photo Manuel Lopez photo Eli Rios
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.