For those of you who have not heard of Oreoleptidae, particularly the American entomologists among you, this should come as a shock. The other new families of flies are from places like New Zealand and Chile, so perhaps some of you might say 'oh, these are super-rare flies from exotic locations, I would never see, hear, or collect these new families.' Oreoleptidae, however, is found in the United States of America. Specifically Idaho. It is also the only one of these new families for which the larvae are known. In fact, no adult has ever been collected in the field; imagines have only been reared from larvae.
The larvae of this singular family were collected in the Rocky Mountains from Montana and Idaho north to Yukon. They were tentatively assigned to Athericidae or Tabanidae by several experts but their formal description was held off until adults were reared. Zloty, Sinclair, and Pritchard described Oreoleptis torrenticola from material collected in Alberta, Canada, and gave reasons why it deserves a separate family level designation in Systematic Entomology (2005), 30, 248-266. The time it took entomologists to find and describe Oreoleptidae is fully attributable to its elusive, specialized biology.
Oreoleptis larvae are found in deep wells and very fast torrential streams. The larvae have durable cuticle but are flexible. They have 2 pairs of prolegs per abdominal segment and move quickly in their specialized habitat, preying upon mayflies nymphs and larval caddisflies. There are no thoracic prolegs, so the larval head is to the right in the photo below. The pupae have been found in sandy soil, gravel, and on foliage surrounding streams above the spring runoff high water mark. A new population was recently found in the Cascade Range in British Columbia. Nothing is known about the adult biology. They might be extremely short-lived as adults similar to other mountain stream specialists flies such as mountain midges (Deuterophlebiidae), but the presence of a proboscis (absent in deuterophlebiids) suggests otherwise. Why adults have never been found in nature is a mystery.
Oreoleptis torrenticola is dear to me because it is an outgroup in the molecular phylogenetic study of Tabanidae on which I am working with Shelah Morita and Brian Wiegmann. Elucidating the relationships within the Tabanomorpha is not the purpose of the study so I can't say much for certain, but Oreoleptis is decidedly not a member of Athericidae nor Tabanidae. This agrees with Zloty, Sinclair & Pritchard who placed it as sister to Athericidae + Tabanidae. For more details, please read Zloty, J., Sinclair, B & G. Pritchard (2005) Systematic Entomology 30:248-266. Thanks to Brad Sinclair for looking over this post. Check in for the 5 more new fly families described since 2002!
Adult Oreoleptis torrenticola . Note the odd humpbacked shape, wing venation, and antennae. From Zloty, Sinclair & Pritchard 2005. Thanks Brad Sinclair for letting me use this image.
Larval Oreoleptis torrenticola . The head is to the right and the prolegs are to the left. From Zloty, Sinclair & Pritchard 2005. Thanks Brad Sinclair for letting me use this image.