From lakes and salt marshes to farms, ranches, and even the zoo, it is hard to avoid the annoyance of horse flies and deer flies, family Tabanidae. Not only are the bites of these giant flies excruciating, our immune system reaction to them can be serious.
One stunning features of tabanids is their enormous compound eyes. Most species sport a psychedelic pattern of rainbow stripes (horse flies) or spots and blotches (deer flies). Don’t get mesmerized, lest you give the beast time to bite.
Scissors for a Mouth
Horse flies and deer flies don’t painlessly sink a proboscis into you like a mosquito. No, they use modified mouthparts that first slice you open, and then lap up the blood as it flows freely from the wound. Remember the usual victims of these flies are thick-skinned hoofed mammals, not thin-skinned humans. Components of horse and deer fly saliva include anticoagulants, so long after the insect has left, you continue to bleed.
Life and Times of a Tabanid
Only female horse and deer flies bite. Males sometimes drink flower nectar, as will females. Eggs are laid in clusters on vegetation or other objects near water. Larvae are leathery maggots that live in the wet soil of bogs and marshes, or the edges of ponds and streams, where they prey on other organisms. Mature larvae pupate on land, and an adult fly eventually emerges from the pupa. The larva stage alone may span 2 years.
Allergies, Infection, and Diseases
Tabanid bites can be serious, beyond typical pain, swelling, and itching. There are several anecdotal reports of tabanid bites inducing anaphylactic shock, a life-threatening condition, but little research to prove it. Meanwhile, if you are bitten, remember any open wound is vulnerable to infection. Cleanse and cover the bite. Thankfully, risk of diseases from horse and deer flies is remote. Deer flies are proven mechanical vectors in the transmission of tularemia (aka “rabbit fever” or “deer fly fever”). Horse flies definitely transmit Equine Infectious anemia (“swamp fever”) to horses; they can also transmit anthrax.
Wearing a hat discourages deer flies that circle your head. Wear long-sleeved shirts, and pants, too. Do use repellents with 30% DEET as the active ingredient, such as Ben’s® 30% Deet insect and bug repellent.