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THE NATURALIST
by Dave Evans

Insect Kings of Kodiak
August 14, 2002

Through the summer at Fort Abercrombie, it becomes apparent to me that there just isn't the insect variety I'm used to seeing in more southern regions, and what species there are tend to be diminutive. That small size doesn't mean they're inconsequential, as we find out on some windless days when the whitesox start working us over.

It's interesting to consider, though, why the insect pickings are so slim on Kodiak. Our short summer season restricts insects either to fairly small species with short life cycles (those little flies like whitesox) or types that can take advantage of special adjustments to situations they're likely to encounter on the Island. Many, for instance, appear to have the physiological ability to be active at much lower temperatures than some of their southern cousins. That attribute allows feeding and flying from early in the morning until late in the evening, capitalizing on the long days of the short Kodiak season.

Some of the other insects, like bumblebees or yellow jackets, take advantage of social organization, and cooperate to bring offspring up to adulthood through the short summer.

Yet another way to avoid the rigorous seasonal requirements of Kodiak is to associate with some stable environments that allow exemption from seasonal fluctuation--Kodiak's lakes and ponds. Water is a great moderator of temperature change. Animals that live under water can stay active all year round. They may slow down a bit in winter, but living in water allows them to begin activities much earlier in spring and extend them to later in fall. It also allows them to have longer lives and grow larger.

Dragonflies are perhaps the Kodiak insects that have most effectively exploited the aquatic life cycle. At this time of year they are the largest flying insects that we have, and we can see them methodically cruising the Island's meadows and shorelines looking for smaller insect prey. With their powerful blade-shaped wings, they are magnificently adept fliers. As large insects, they have the Kodiak skies pretty much to themselves. Besides size, they have other features that contribute to their status as the dominant insect predators on Kodiak. Their eyes cover most of the head (theirs is a highly visual world), and grappling legs hold prey up against their jaws so they can feed on the wing. A single dragonfly can capture and feed on up to 600 insects per day.

The early stages of the dragonfly's life, not the aerial adults, represent the most significant adaptation to Kodiak's seasonality. Immature dragonfies are perfect examples of life forms that have exempted themselves from seasonality by developing in lakes and ponds. They can live several years in these stable aquatic environments, build up some size, and then metamorphose to the flying form with which we're familiar. Even in their pond habitats, they are the dominant insect predators, using an extensible appendage on the head to grab anything swimming by, including small fish.

I never fail to be impressed by the different survival strategies I see around us on the Island. In this case, we have Kodiak's largest insects going through most of their development in a habitat where we don't see them, and they circumvent the short-season requirements that other Island insects need to meet. That developmental secret has allowed them to rule the insect airspace over Kodiak.

David A. Evans, Naturalist, Fort Abercrombie State Historical Park


http://www.kadiak.org/naturalist/insect_kings.html Updated 2002 August 14

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