For the most part flies are not an insect I get overly excited about. However, the enigmatic family Acroceridae are the exception. I’ll start sharing some interesting genera from time to time – the morphology of the family is amazingly diverse. Most of my days are spent at the museum inventorying our massive collection of over 16,000 Acorcerids (aka small-headed flies). That may not sound all too impressive when you compare it to other more abundant families (and it does pale in comparison to the over 17,500,000 other specimens we do have in the museum); but it turns out to represent many, if not most, of all known specimens for the entire family. While there are likely large assemblages of these flies in other institutions, the California Academy of Sciences can easily claim the record ever since receiving the collection of Dr. Evert I. Schlinger (who occasionally comes in to work from the museum).
Acrocerids turn out to be a rather difficult group to study because of how rare they are in nature, their parasitoid biology, and how difficult they can be to catch on the wing. Their large thorax is packed with muscles that rocket the fly through the air – so if you don’t catch them at a flower you’re left longing for a Malaise trap. Ev did tell me one story of learning to catch these on the wing in Costa Rica. You stand downwind from a colleague in the field – as soon as someone hears something zip past, you swing wildly hoping to snare the fly by chance… it does work every once in a while. These flies are also the only known endoparasites of adult spiders (there may be a record of a Tachinid…). The above genus,
NeoLasia, is a parasite of Theraphosid tarantulas (something like Aphonopelma). As a larvae the fly works its way up the legs of a spider and burrows into the abdomen where it then settles in next to the book lung and pokes a little breathing hole. Then it waits patiently for the spider to near maturity. With female tarantulas, the fly could be dormant for decades. Eventually something akin to the movie Aliens happens and the larvae feeds on the internal organs of the spider then emerges to pupate. But figuring out whether or not a spider has a parasite is impossible without a dissection – so large collections of live spiders must be maintained to obtain host records. Parasitoid biology is just so cool.
The above specimen (Lasia klettii
a new, unnamed, species) was collected in 1977 by Schlinger near the town of Alamos, Mexico – on flowers with the likely mimic model, a Chrysomelidae beetle (beetle people, any ideas beyond family?).