Those of you who follow me on Twitter (@CatofOrg) may have already seen these guys, but I thought it worth putting them up here as well. Because sometimes you come across an animal that just makes you stop, blink, and exclaim, "What the creeping jayzus is that!". Ladies and gentlemen, the Celyphidae.
Celyphids are flies that are doing their damnedest to look like a beetle (and are hence, unsurprisingly, commonly known as beetle flies). The scutellum, which in most flies is a relatively small lobe of the thorax sitting behind and between the wings, has become massively enlarged and overtops the abdomen. The wings (which are full-sized and fully functional) slip in underneath the scutellum when folded back. Just to add to the overall beetle-osity of the thing, celyphids can be very shiny and metallic (check out the blue-black item here). The function of this giant scutellum is unknown; protection is the first thing that comes to my mind, but I don't know if the scutellum is any more sclerotised than the rest of the animal. One suggestion that has apparently been made is that the scutellum may provide extra buoyancy in flight (Tenorio 1972), to which I ask, is it hollow or something?
Celyphids are found in tropical Asia and Africa (all the photos on this page except the last were taken in Singapore). They are closely related to the more widespread family Lauxaniidae, and have been treated by at least some authors as a derived subgroup of the latter (some lauxaniids also show a degree of enlargement of the scutellum). The larvae of celyphids feed on rotting vegetation.
Tenorio, J. M. 1972. A revision of the Celyphidae (Diptera) of the Oriental Region. Trans. R. Ent. Soc. Lond. 123 (4): 359-453.