A rather larger - and much more confusing - family than last month's Micropezids, meet the Thick Headed Flies:
|Conops (unidentified species) in Chongwe District, Lusaka, Zambia; February 2013.|
These colourful, wasp-like flies have had a tumultous taxonomic history; bouncing between the Aschiza (along with Hoverflies such as Metadon inermis) and the Schizophora (along with the greatest diversity of modern flies, including such oddities as the Stalk-Eyed Diasemopsis meigenii), but while genetics support its relationship to the Schizophora, its position therein remains imperfectly resolved (Gibson et al, 2010); but the family itself has been quite intensely studied (e.g. Gibson and Skevington, 2013).
|Sicus ferrugineus Scopoli, 1763, |
in Chichester, West Sussex, UK; July 2013.
Their life-habits are fairly remarkable, too; while adults are often found visiting flowers, they spend their larval stages eating other insects - usually bees (as is the case with Sicus ferrugineus Scopoli,1763 from the UK) or wasps of various families; a few species are known to parasitize cockroaches and crickets.
Wasps and bees are by no means an easy target for a fly with a limited physical arsenal; no powerful sting, no heavily-built, piercing mouthparts (which would be somewhat counterproductive, at any rate); and so many get around this problem by looking remarkably wasp-like:
|Archiconops pseudoerythrocephalus Stuke, 2004 on banks of Luangwa; Eastern Province, Zambia, April 2015.|
|Unidentified Mammoth Wasp (Scoliidae) from Lusaka, |
showing similarity of appearance to that of Archiconops.
But there are other risks to hyperparasitism; evolutionary risks. While the wasp's populations are at the mercy of fluctuations in beetle populations, and must remain at a relatively low level to ensure that they do not begin to exhaust their host populations, the fly's survival depends both on the wasp and on the beetle, and if either of them has a bad year, the fly's population will plummet - and with reproductive rates necessarily low to avoid causing a crash in host populations, they can take generations to recover, and are rarely - if ever - common.
|Conops cf aurantius Brunetti, 1925 in garden in Chongwe, Lusaka, Zambia; |
only a handful of these flies will be seen per year even in most rural environments.
Identification can also prove surprisingly complicated; although the flies are very distinctive as far as flies go - even if they may, at a glance, they may be mistaken for the wasps they mimic - there are a precious few others that can be strikingly similar.
|Systropus Weidemann, 1820, is a wasp-mimicking bee-fly (family Bombyliidae)|
that can bear a striking resemblance to some Conopids. Chongwe, February 2016.
|Physocephala rufipes (Fabricius, 1781) |
in Bosham, West Sussex, UK
The fly immediately above is a Zambian example of Systropus Weidemann 1820, an unusual genus of Bee-flies (Bombyliidae) which, like most Conopids, closely mimics wasps. Physocephala - a very widespread genus of Conopid that also occurs in the region (although the species shown is the British Physocephala rufipes (Fabricius, 1781)) - can be very similar; and they are probably most easily distinguished by their eyes; in Conopids, these are always widely separated, while in Systropus, they meet at the top of the head.
There are numerous other distinctions, particularly in the dramatic external genitalia of many female Conopids; but the widely separated eyes are a very prominent feature of the Conopids, and help to mark out this (un-cooperative) Conops cf elegans Meigen, 1824 as a member of the family [NB - various flies in various families ALSO have widely separated eyes, but are not nearly so Conopid-looking as Systropus].
|Conops cf elegans, Meigen 1824. |
Banks of the Luangwa River, Eastern Province, Zambia, April 2015.
And just to be going with, the European Conops quadrifasciatus De Geer,1776 in a West-Sussex Garden. Although this species was only formally described some 18 years after Linnaeus' Systema Naturae transformed entomology in 1758, the genus - which we have encountered almost throughout this post - is actually one of the first described of all invertebrate genera*, as one of only 10 genera of flies that Linnaeus actually described.
|Conops quadrifasciatus De Geer,1776 in Bosham, West Sussex, UK; August 2013.|
More details about Conopid life-histories can be read in Gibson's 2011 thesis on the family, which is (unlike the other two Gibson papers) freely available online.
A good starting place for Conopids in Southern Africa is O. Kröber's The Conopidae of South Africa, in Volume 14 Annals of the Transvaal Museum; this is a very elderly paper, however, and it is always worth checking on the Diptera Nomenclator that the names Kröber uses are still appropriate to species in south Africa (e.g. Conops erythrocephala Fabricius, 1794 in Kröber's work almost certainly refers to Archiconops pseudoerythrocephalus Stuke, 2004)
*Incidentally, and as I was completely mis-explaining to a much-more-knowledgeable entomologist the other day (As a general rule, if I'm trying to explain something genuinely interesting to someone cleverer than me who doesn't know about it, I will forget everything that is inside my head and be embarassingly wrong about everything), Linnaeus Conops - and all his other invertebrate genera - lag behind several European spiders. Although no longer in its original genus, Enoplognatha ovata (Clerck, 1757) - the very first post on this blog - is one of those species which is still listed as being described one year before Linnaeus' Systema naturae, which is officially considered the starting-gun for the binomial naming system in invertebrates - to avoid taxonomists having to trawl through Pliny and older works to see who deserves the truly initial credit, so the whole thing is a bit of a scandal.