Deer flies, also known as yellow flies, are pests to all mammals – that means you!  They have distinguishing gold or green patterned eyes. Deer flies belong to the family commonly called tabanids. A close cousin is the larger horse fly.

They are found in damp environments, such as wetlands or forests. They lay clusters of shiny black eggs on the leaves of small plants on/or near water.

Adult flies are active in late spring to early fall. The life cycle varies considerably between sub-species, anywhere from 70 days to two years.



  • Deer flies lie and wait under bushes and trees for a host to pass by. Sight is the primary sense for finding a host, however, they are also attracted to:
  • Carbon dioxide from the breath of mammals  – don’t breathe,
  • Perfumes – don’t bath,
  • Movement – don’t move,
  • Dark colours – wear light colours.
  • Attacks can occur during all daylight hours.  Peak feeding times are the 3 hours after sunrise and the 2 hours prior to sunset. Attacks are more frequent on overcast days. They particularly enjoy your head, hairline and scalp. Wear a hat or bandana!

The Nasty

Only female deer flies feed on blood, males collect pollen. When feeding, females use knife-like mandibles to make a cross-shaped incision and then lap up the blood. While feeding, an anticoagulant is injected into the wound which causes the blood to flow freely. The bite and saliva of the fly can result in discomfort, pain, itch and a general allergic reaction.

Since they are intermittent feeders, horse and deer flies are transmitters of diseases.



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