Gigantic black horse fly

An unwelcome guest at any family picnic…

female black horse fly

A gigantic black horse fly, with scissor-like mouth parts ready to slice into tender skin.  About 1.5 inches in length, and a solid black color everywhere, this is a fearsome beast.  A space between the wrap-around eyes means this is a female — the sex that bites and draws blood from man and beast.

female black horse fly mouth parts

Within the vertically oriented sheath of mouthparts below the eyes are scissor blades that slice and shred their way into the skin of tough cow or horse hide with ease.  A sponge-like structure on the end of the proboscis then mops up the blood that pools on the skin.  

Female horse and deer flies require a blood meal to obtain sufficient protein to complete egg development. Males lack the cutting mouthparts and feed only on nectar and pollen.  These biting flies are serious pests of livestock, not only because of their annoying buzzing near sensitive spots on the face, but because they take such large quantities of their hosts’ blood (30 flies can suck up 1/3 pint of blood in less than 6 hours).

Following their blood feast, female Black horse flies deposit their eggs on or near aquatic vegetation where the larvae will develop over the next couple of years, feeding voraciously on aquatic insects or snails.

female black horse fly

A fly to reckon with…

2 thoughts on “Gigantic black horse fly

  1. Great macro shots, Sue, of a horse fly that looks big enough to put a saddle on and ride. In general, I like insects, but I have a whole lot less fondness for those that will administer painful bites to me. Those mouth parts are scary-looking! Ouch,

  2. Great pictures. I did not realise that they could be so debilitating for livestock nor that they did not have piercing mouthparts. That explains a lot of the “ouch” factor. Amelia

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