Thursday, September 7, 2017

Horse Fly Larvae

Horse Fly Larva
We recently wrote about the horse fly, the big buzzing pesky devils whose females bite to obtain blood necessary to produce their eggs.  I just came across one of their kids deep in a gravel bar.

I was with Deb Finn and Nathan Dorff of MSU, exploring gravel bars along Bull Creek as research sites.  We hiked up Peckout Hollow, an ephemeral drainage that has been dry for weeks.  There we found an uprooted tree and a deep hole washed out by a previous flood.  In the bottom there was a small shallow water pool a foot in diameter.  Nathan began digging away the gravel and came up with this horse fly larva.

Black Horse Fly Larva - Tabanus atratus *
"The larvae are long and cylindrical with small heads and twelve body segments. They have rings of tubercles (warty outgrowths) known as pseudopods round the segments, and also bands of short setae (bristles). The posterior tip of each larva has a breathing siphon and a bulbous area known as Graber's organ." Wikipedia on Horse Fly

Horse fly larvae generally are found in freshwater streams and moist soil.  Finding this one far from the creek is a reminder that water continues to flow under apparently dry gravel bars.  They even found a small crawdad!  Nathan's interest is in studying the ecology of water under the gravel and the invertebrates living there.

My favorite way to see a horse fly.
The larvae of most horse fly species are predators, feeding on worms and insect larvae although some of the larger species will attack tadpoles, frogs and toads. Unlike a lot of fly larvae, mine seen in this video manages to get around quite well with its six stubby legs.  They can have toxic saliva that helps to subdue their prey.  Depending on the species they can go through 6 to 13 molts before forming the pupa.  There is one generation per year but some species will develop to adulthood over 2 years.**

Having recently been tormented by some of its kin, I felt no guilt in keeping this specimen to the end of its life.  It may mean one less bite on my next hike up the hollow.

I found it was still alive in the specimen container of water a month later as seen in this video.  I am now keeping it in water filled with ostracods to see if I can get it to pupate.*
*  Note 11-8-2017:  Identified as Tabanus atratus by Dr. David Bowles who published a study on the species in 2008.
**Purdue University Entomology Extension

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