A 50-million-year-old midge

Several of the insect fossils collected from the Green River Formation (45–50 mya) that I am photographing appear to be flies, and specifically members of the “primitive” suborder Nematocera. This is not surprising, as the G.R. Formation of Colorado, Utah, and Wyoming, is composed of shales derived from volcanic ash sediments that were laid down in a system of large, shallow lakes. Most (all?) nematoceran flies are aquatic to some degree in the larval stage, thus the adults are also closely associated with such habitats for mating and egg laying.

Diptera: Chironomidae | USA: Colorado, Garfield, Hwy 139, Douglas Pass

Diptera: Chironomidae | USA: Colorado, Garfield, Hwy 139, Douglas Pass

This particular fossil looked to me a lot like the more elegantly preserved fossil of another fly that I posted a few days ago, which at the time I thought represented a member of the family Mycetophilidae (fungus gnats) or Sciaridae (black-winged fungus gnats). Several knowledgable specialists offered their opinions in comments at this site and at Facebook’s Diptera forum (my thanks to all who offered their opinion), with most settling on Mycetophilidae and Vlad Blagoderov further suggesting subfamily Mycetophilinae. The fossil posted here seemed to me to represent a dorsal view of the same species, but, of course, I’m a coleopterist—so what do I know? Indeed, dipterist Dr. Chris Borkent believes this is actually a species of Chironomidae (common name simply “midges”)—also a nematoceran but differing from Mycetophilidae by their longer front tarsi and longer, relatively narrower wings. Males of the family have thickly plumose (“feathery”) antennae, which are not visible in this specimen and thus suggesting it might be a female. I wouldn’t doubt Chris’ identification  for a second, as he comes from good stock—his father is Art Borkent, a world expert on several families of nematoceran dipterans. Art also agreed after seeing the photo that it looked like a female chironomid midge, so that is what I am going with. Thank you, Chris and Art, for your help in identifying this fossil!

Complete fossil specimen (63 mm x 52 mm maximum each axis).

Copyright © Ted C. MacRae 2012

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About Ted C. MacRae

Ted C. MacRae is a research entomologist by vocation and beetle taxonomist by avocation. Areas of expertise in the latter include worldwide jewel beetles (Buprestidae) and North American longhorned beetles (Cerambycidae). More recent work has focused on North American tiger beetles (Cicindelidae) and their distribution, ecology, and conservation.
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2 Responses to A 50-million-year-old midge

  1. Very cool finds Ted! As for larval nematocerans, there are some that are not aquatic (several Tipulidae are found under bark for example), but they are generally restricted to damp, humid habitats.

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