The other day I found an enormous bug in my house.  I had no idea what it was when I saw it, so I grabbed my camera and put on the 65mm macro lens to make sure I got some detailed shots of what I figured might be the important characters.  I wouldn’t have even recognized it as an insect, since at first it seemed to have four rather than six legs.  However, I noted that the third pair of legs was actually present, but that one was atrophied to a long, flexible, backward-directed appendage incapable of locomotory or weight bearing function, and that the other leg was missing completely – perhaps aborted during embryogenesis due to some injury or genetic malfunction.

As I said, the bug was enormous and jet-black, although I can’t be sure that is its real color because it was covered so thickly with long, thin, semi-recumbant setae that the surface was completely obscured.  I know a lot of acalyptrate flies are thickly covered with setae, but I’ve never seen a fly with setae so densely packed as this.  The large eyes also pointed towards something in the Diptera, but since it was wingless that narrows the choices down to just a few flightless, ectoparasitic families.  However, most ectoparasitic dipterans have well developed compound eyes, while this one had only two (albeit very large) ocelli.  The above shot gives a decent view of one of them.

The bug was active and alert and quite difficult to photograph, but I managed to get this shot of its mandibles.  The numerous points remind me of the mandibles of certain predaceous coleopterans, which combined with the somber coloration made me think it might be some kind of ground beetle.  If so, it would be the largest ground beetle I had ever seen.  However, I noticed that the mandibles opposed each other in a vertical rather than horizontal plane – something I’ve never seen with ground beetles (or any kind of beetle), nor have I seen a black beetle with the teeth on the mandibles tipped with such a contrasting white coloration.

An even closer view of the white-tipped mandibular teeth shows that each point bears a median groove.  Whether these are wear patterns from mandibular occlusion or serve some feeding function is unknown.  If it is predaceous, as I suspect, they could form channels for directing liquids imbibed from their prey towards they hypostoma.

The frons was the only glabrous part on the entire body (besides the two ocelli and the undersides of the tarsal pads), and its bulbous form with a median groove reminded me of certain auchenorrhynchous hemipterans that have a similar frons containing a cybarial pump to provide suction for obtaining sap from plants.  However, again, the distinctly toothed mandibles suggest this is a predaceous insect, and as far as I have been able to tell all auchenorrhynchans are exclusively plant feeders.

Eventually the insect became quite agitated and began struggling to escape.  I tried to confine it so I could complete my examination and make sure I had enough photos to get an ID, but it began displaying its mandibles in a suggestively threatening manner.  I decided to let it go at that point and hoped that what I had photographed to that point would be sufficient.  Although I still haven’t figure out what insect this is, I don’t think it is a new species since I’ve found quite a few photos on Flickr that seem to show the ocellus of this or related species.  Puzzlingly, there is no indication on any of these photos which insect group they belong to, so I’ll have to keep searching in an effort to come up with an ID.  I’ll post an update here if/when I can find this out.  Until then, this site has some information that might prove useful.

Copyright © Ted C. MacRae 2011