Column: The dreaded deer fly

Published 2:42 am Thursday, September 23, 2004

By Staff
With summer winding down, so too, thankfully, are the biting bugs. For me, the most feared of these is deer flies. Mosquitoes you can fight. A dash of bug dope renders them to just a minor annoyance of buzzing in your face. Should one have the audacity to get past the bug dope and bite they're slow enough that you can easily exact the ultimate revenge. Deer flies are a whole different story. They get a whiff of bug dope and say, "Yum, this cake has frosting on it." While the mosquito trundles along at wheel chair speeds, the deer fly is an F-16 complete with afterburners. You're not about to get a decent whack at her. Worst of all, the deer fly is fearless. It takes you on mano-a-mano. It is going to drive home the kamikaze attack or die trying.
If you've been along the edges of woodlands during the hot summer months you know what deer flies are. There are several species but they look quite similar, about house fly size with light colored, tan to gold bodies and transparent wings with black mottling. While the books say they frequent deciduous or mixed forests they are really an edge creature. Seldom am I attacked while deep in the woods, it's when you're along the edges that they can send you running with a relentless assault nearly as bad as a swarm of irate wasps. Another key feature of their habitat is water. A lake or slow moving stream is essential for larvae development. They are most active on hot, sunny days with low wind.
In terms of life style they are similar to mosquitoes. Plant nectar and juices are their food source. Only the females bite as a blood meal is required for egg development. Deer flies are more sight oriented than mosquitoes. Mosquitoes usually first start licking their chops when they detect carbon dioxide given off by their victim and only use sight for the final attack coordinates. Deer flies alert to carbon dioxide some but it's spotting a dark moving object that really whets their appetite. While mosquitoes don't seem particularly color oriented, just anything dark, deer flies love the gaudy. Blue, the brighter the better, is their color of choice followed closely by red. To lessen chances of detection by any biting insect wear light colored clothing with neutral tones like khaki.
After mating females lay a cluster of shiny black, spindle shaped eggs on shoreline bushes. In five to 12 days the larvae hatch and drop to the ground where they burrow down into wet mud. There they remain from one to three years. In late spring the larvae migrate to drier ground and develop into pupae. In another week or so the adults emerge.
Deer flies can be more than annoying. Some may carry bacteria that cause tularemia which can further lead to pneumonia, meningitis and infection of bones and internal organs. They're also suspected of transmitting things like anthrax, hog cholera, equine infectious anemia and even Lyme disease. With knife-like mouth parts they cut through the skin to cause blood flow. They spit anticoagulant saliva into the wound as they sit and lap up the blood for up to three minutes. Us humans with our wonderful appendages feel the bite and immediately take a whack at them so rarely is much, if any, potential disease carrying saliva introduced. Other animals aren't so fortunate, they must just endure.
Deer flies are a formidable adversary. Standard bug repellents are largely ineffective. Repellents containing permethrin work and are used on livestock but permethrin is harmful to humans. At this point controlling deer fly numbers is impractical. Eliminating their wetland habitat is environmentally unacceptable. Larvae control with insecticide pollutes the water and adult spraying requires broad spectrum insecticides which are harmful to birds, fish, desirable insects and mammals. Experiments with larvae control utilizing bacteria, similar to the method so effective in mosquito control, are showing promise but that's a ways off yet. Until then we'll just have to keep swatting. Carpe diem.