Mosquito Molestation Motivates Minor Migrations
Above the Salcha River, Pipeline Mile 495---Enough mosquitoes perch on my tent these nights that they could airlift Jane and I to their favorite bog if they all latched on and lifted at once. Fortunately, mosquitoes don't have very big brains. The females do have a lust for blood, though, enough to alter the behavior of man and beast.
Frank Morschel recently studied how caribou were affected by the flying devils of the north. Morschel did his research in the Alaska Range during the summers of 1994 and 1995 to earn a master's degree at the University of Alaska Fairbanks.
Morschel traveled on horseback to reach the caribou of the Delta herd, a group of caribou that spends its summers in a wide patch bordered to the north by the Tanana Flats, to the south by the Denali Highway, to the East by the Delta River, and to the west by the Parks Highway.
While wolves currently get all the press as being a major factor in the decline of caribou herds, caribou face other significant perils, such as occasional lack of food. Insects, specifically mosquitoes and oestrid flies, also cause the beast plenty of misery.
Six- to ten thousand mosquitoes can simultaneously draw blood from one caribou, Morschel wrote, citing the work of a Russian scientist who also estimated that individual caribou in a certain region of Siberia lost more than five pounds of blood per summer to mosquitoes.
In addition to blood loss, mosquitoes often drive caribou to higher elevations and snow patches, where forage isn't as good. Insect-harried caribou also don't rest as much. Morschel found that caribou spent much less time lying down during insect season.
Another caribou defense mechanism is crowding in large groups. While this relieves the insect pressure on individuals, Morschel found caribou in those large groups spend less time feeding and more time standing when compared to groups that were more spread out.
Morschel observed the weather conditions mosquitoes thrived in; his results are of great interest to me now. He found mosquitoes didn't become pesky until the temperature reached about 45 degrees Fahrenheit. He cited other researchers who found mosquito harassment increased with increasing temperature to about 68 degrees. Above 68, mosquitoes become less active, and the pests take cover at the upper threshold temperature of about 82 degrees.
I just noticed this in action. I ate breakfast shirtless on the Salcha River because there were no mosquitoes. It was about 75 degrees in the sun. After Fred Margraf of Salcha ferried me across the river (thanks, of course, to Jane's fame), clouds moved in and the temperature dropped 10 degrees. I had to wear my bug jacket all the way up a long, steep hill. The climb rewarded me with great views and a mosquito-foiling wind.
Morschel wrote that mosquito activity decreased with increasing wind speed up to about six meters per second. Speeds faster than that apparently ground mosquitoes. Even though Morschel's thesis now requires a very big rock to hold it by my side, I'm rather thankful for this bug-baffling breeze. If it would only stay with me as I drop into the next swampy valley.
