Bug Power

Mosquitoes are a force to be reckoned with.

NPS/Kyle Joly

With an estimated population of 17 trillion in Alaska, mosquitoes are a force to be reckoned with. While far less numerous, other insects, such as warble flies, can also have major impacts. Mosquitoes suck the blood of their hosts to help produce eggs; the scientific term for this is that they are hematophagous. Warble flies lay their eggs on caribou so that their larvae can burrow into the caribou skin and feed on its body, making warble flies an endoparasite. The most obvious impacts of these insects on caribou are behavioral. Caribou will shake, walk, and even run away from insects. Often they will go to habitats with little vegetation, like river gravel bars and snow fields, and group together to reduce insect harassment. These groups of caribou are called aggregations and can number in the hundreds of thousands. But the more time caribou spend avoiding insects in poor habitats, the less time they have to spend feeding. This is critical in the Arctic because the growing season is already very short. If caribou don't get enough to eat during the summer, their calves can have lower survival rates and cows can fail to gain enough weight to be able to become pregnant in the fall. If this happens to enough caribou, the entire population can be negatively effected.

Caribou are an important food source for humans, wolves, golden eagles, wolverine, and bears, and their carcasses are used by scavengers like foxes and ravens. Thus, if insects are impacting caribou populations, they are indirectly affecting all aspects of Arctic environments. With the Arctic warming twice as fast as anywhere else, the impacts of insects on caribou may increase as insects thrive in warmer temperatures.

Large numbers of caribou, aggregations, crowd together around bodies of water or snowfields to get some relief from insect harassment.

NPS/Kyle Joly

Behavioral, Physiological, Demographic and Ecological Impacts of Hematophagous and Endoparasitic Insects on an Arctic Ungulate

Abstract

Animals that deliver a toxic secretion through a wound or to the body surface without a wound are considered venomous and toxungenous, respectively. Hematophagous insects, such as mosquitoes (Aedes spp.), meet the criteria for venomous, and some endoparasitic insects, such as warble flies (Hypoderma tarandi), satisfy the definition for toxungenous. The impacts of these insects on their hosts are wide ranging. In the Arctic, their primary host is the most abundant ungulate, the caribou (Rangifer tarandus). The most conspicuous impacts of these insects on caribou are behavioral. Caribou increase their movements during peak insect harassment, evading and running away from these parasites. These behavioral responses scale up to physiological effects as caribou move to less productive habitats to reduce harassment which increases energetic costs due to locomotion, reduces nutrient intake due to less time spent foraging, and can lead to poorer physiological condition. Reduced physiological condition can lead to lower reproductive output and even higher mortality rates, with the potential to ultimately affect caribou demographics. Caribou affect all trophic levels in the Arctic and the processes that connect them, thus altering caribou demographics could impact the ecology of the region. Broadening the definitions of venomous and toxungenous animals to include hematophagous and endoparasitic insects should not only generate productive collaborations among toxinologists and parasitologists, but will also lead to a deeper understanding of the ecology of toxic secretions and their widespread influence.

Joly, K., O. Couriot, M. D. Cameron, and E. Gurarie, E. 2020. Behavioral, physiological, demographic, and ecological impacts of hematophagous and endoparasitic insects on an Arctic ungulate. Toxins 12:334. doi:10.3390/toxins12050334