I’m in the ready position. Knees flexed. On the balls of my feet. Arms out in front bent just less than 90 degrees at the elbow. Almost like a boxer except more at waist level and my hands are outstretched, palms facing each other, slightly less than shoulder width apart. Back to the wind, bare feet pressed into the sand. I am ready! Bring them on!
I’m camped along the Yukon River. Having gotten up early recording bird songs I have stopped early. I am weary and just want to lay down and take a nap. But it is the heat of the day and the sun beats ruthlessly on the tent. I seek relief from the heat and go back outside where there’s a breeze. I could peacefully lay down and sleep out here except for one thing: I have to run the gauntlet of horseflies.
Like a real live video game, I kill one and another comes on. I kill that one and two more come on. But this certainly isn’t a game. Not for me nor for them. It’s about survival. For them. For me. They need blood to help develop their eggs. I could relax more if I could sit outside without constantly watching my back for the fly that will deliver instant curse inducing pain. It’s stressful. When I was a kid and had seemingly infinite energy I would’ve enjoyed the game. Now, in my mid 40s, energy is of limited supply and I like to conserve it for paddling. But… if only I could eliminate them all… I would be in peace. Right? SLAP! Another one down.
Horseflies are members of the Order Diptera which includes all the flies, including our other favorites like mosquitoes, gnats, noseeums, and houseflies. There’s at least 30 species of horseflies in Alaska. They come out on hot clear days with intense sun and, in my experience, can endure pretty strong winds. Horseflies would find me in the middle of the river and camped on enormous sandbars, far from vegetation.
In Alaska I’ve only really suffered through them on the Porcupine River and then this year on the Yukon. I can’t recall ever having seen one at my place in Talkeetna. And, I worked for 5 summers on the lower Yukon, saw some hot muggy days and don’t even remember a horsefly. What was it about this year, when I saw multitudes of them? At several of my camps I killed 30 to 40 of them and still there were more. When I recall horseflies from my canoeing days in the Adirondacks and Boundary Waters I only remember a couple at a time hanging around. It seemed like they were easy to kill. And at least down there the sun would go down at a reasonable hour and they would vanish. But up here in the Alaskan interior the horseflies would get up as early as 7 am and be active all the way until 10 pm.
If it doesn’t hurt when you swat one… she’s not dead. If you don’t shmoosh her until she oozes… she’s not dead.
SLAP!! She falls to the ground. STOMP!! And I give a few twists with my foot. And just for good measure, kick some sand over her and stomp again.
I’m normally very peaceful and considerate of other living creatures. Even mosquitoes. Sure, they can be annoying but I don’t get vengeful toward them. I let the ones go who got my blood fair and square and if I can’t feel them biting me I let them be. But horseflies have brought out the worst in me.
They fly noisily- sounding like miniature fighter jets and acting just as ominously, circling my tent, waiting for me to come out. But they can land without detection and bite almost simultaneously. This is what’s so maddening about them. I was only actually bit 3 or 4 times this whole summer which amounted to about 4 seconds of actual pain. But I suffered through hours of being tortured by the thought of this pain.
Their bite is so painful I instantly react and that fly is either dead or escapes but without the blood she was pursuing. Does she get any blood in this first painful incision? It seems like few animals could endure the torture of standing still while a horsefly gets all the blood she needs. It seems counterproductive for a horsefly to bother with humans. Unless someone is unconscious, no one is going to suffer through that pain so the horsefly could have her blood. Nor is anyone going to be so distracted by other things as to be oblivious to the horsefly’s bite. So I got to wondering, how much blood do the horseflies need, how long does it take them to fill up and from whom do they score their blood? Do only the females bite, like mosquitoes? When I got home I did some research.
Back around 1920 a guy named J.L Webb, working for the USDA, studied horseflies and their impact on livestock in Nevada. He determined that it takes 8-10 min. for a female horsefly to fill up on blood on a passive animal. A fill up amounted to about 1 cubic centimeter of blood. Horses would sometimes be driven mad by the flies and run away in their harnesses. Cows put up with the insects a bit more stoically. In Alaska I’m guessing moose are the animals most harassed by horseflies. Bears are vulnerable to the flies in early summer when their fur is short, but normally the flies can only get through around the head. The website of the North American Bear Center shows 2 photos of a black bear sitting on his haunches swatting a horsefly with his 2 front paws, much like a human would.
The sweet innocent males only feed on nectar or honeydew, a sweet exudate left on leaves by some insects like aphids. Females, for basic metabolism, also feed on sweet stuff. But, like mosquitoes, they do the biting, needing blood to develop at least a portion of their egg mass. Unlike mosquitoes who just pierce your skin, horseflies actually slice your skin open with scissor-like mandibles and then lap up the blood. A female can lay from 100 to 800 eggs and lays her egg mass on foliage overhanging good larval habitat. Horseflies in the mid latitudes can finish a life cycle in one year while in more northerly areas they can take 2 to 3 years to complete one. Larvae pass through numerous stages before pupating and becoming adults.
Males hang out in high places, like tree tops, waiting for a female to come along to mate with. Often not noticed by humans, their huge eyes, designed to help them see females flying past, meet at the top of the head.
Insect repellents tend not to work on horseflies because, unlike mosquitoes, they hone in on their prey more visually, seeking out favorite body parts like legs and are also drawn to the warmth and emission of Carbon dioxide. Makes me feel even more unnerved, knowing they’re watching me like a predator.
And, if we think the adults are intimidating, I’d hate to be an invertebrate around horsefly larvae. Here’s what Stephen Marshall says about them in Insects: Their Natural History and Diversity: “Larval horseflies are like spineless subterranean serpents that use fang like mandibles to impale other animals above and below wet ground, paralyzing and liquefying their victims with venomous saliva.” Although they usually eat other invertebrates, including their own kind, they’ve been known to strike fish and small toads.
So what eats horseflies? You’re dying to know. Birds, dragonflies, and parasitic wasps. I am a witness to just one account of a horsefly being attacked and eaten. And what a glorious sight it was. Several years ago I was camped out on the upper Porcupine River in the Yukon Territory on a hot muggy July afternoon. While doing chores in camp a horsefly landed on my bare upper arm. My brain had barely processed this information when down swooped a dragonfly and snatched her right up. The dragonfly settled right there on my arm, less than a foot from my face and squeezed that horsefly to death in its mandibles. And the horsefly stared up at me with that stare that they have, this time a totally helpless one. And then CRUNCH, CRUNCH, CRUNCH. Grinning ear to ear, I beamed down at my hero until nothing was left of its prey but wings and legs fluttering to the ground.
When I grow tired of the futile effort of trying to kill all the horseflies outside my tent I use my other method. Leave the tent door open. They fly in and don’t fly out as easily. After I’ve collected a dozen or so I go in and smoosh them all one by one by one with a dirty sock and fling them out the door. The ground outside my tent is riddled with their carcasses. Then I collapse on my tent floor and try to think peaceful thoughts…..Like about the horsefly I didn’t kill.
One time this summer, I swatted a horsefly on the cargo pocket of my pants. It didn’t hurt, there was too much cushioning, so based on my rule I figured that horsefly wasn’t dead. And she wasn’t. But apparently HAD suffered some brain damage. She flew off but dazedly and straight up into the air looking like an injured cartoon character, eyes crossed and stars streaming up from her head. And up, up, up she rose like Mary Poppins vanishing into the atmosphere.