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Northland Nature: Insects are still active on water surface in late summer

As the days of summer shorten, we see the results of the season. Usually we notice this in the garden produce or berries and fruits that abound now.

As the days of summer shorten, we see the results of the season. Usually we notice this in the garden produce or berries and fruits that abound now.

However, in the world of animals, we also see the products of summer. For many critters, the populations are now at their peak number. This is most obvious with birds, as seen in waterfowl, grouse and songbirds.

Not as easy to note are the populations of insects. With the cooler days, many of the numbers have fallen. Butterflies and dragonflies seen in mid-summer have mostly gone. Bee and hornet colonies are still with us, but no more young are produced now, and as the days get cooler, we'll see fewer and fewer of these insects that nest in nearby trees.

But other insects continue good populations through September. A walk to a lake or pond at this time will reveal many little active bugs on the water surface. This top layer of water is a unique place to live, and most critters are not able to stay here, but a few do. Though one kind of spider, the fishing spider, is able to live here, these impressively large spiders are never as common as two kinds of insects that exploit this habitat: water striders and whirligig beetles.

Water striders get their name from their ability to walk on the water's surface. Not only do they live here, they are seldom seen anywhere else. Water striders are members of the Hemiptera order. The name of this order, also called true bugs, basically means "half wings". They do not have half wings, but with wings crossed over their back, we usually see only part or half of the wings.

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Despite the presence of wings, they take flight only when responding to stressful situations. Insects have six legs, but anyone watching water strider movements over the surface will see only four feet making slight impressions on the water. The other two legs, the front ones, are held under the head, ready to grasp prey.

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Like many other members of Hemiptera, water striders are predators. During these days of late summer, we can see huge numbers of these insects, large and small, skating on the water.

Also abundant now are the whirligig beetles. Oval and black, these insects also live on the surface. Here they seem to spend much of their time moving about on the water. They get the whirligig name from their frequent circular motion. Since they are usually less than one-half inch long, we are not likely to see only one, but the insects live in groups and so are easier to see. Sitting on the surface with front legs extended, they search for other aquatic prey. When danger gets too close they go through their gyrating movements. This distracts the predators and make these beetles hard to see. So adapted are they to this scheme that their eyes are able to look up and down at the same time; almost like four eyes.

Both of these water walkers are now abundant and early September is probably the best time for us to see them. Like other insects, they respond to fall's chill and move into wintering sites on shore.

Larry Weber is author of the "Backyard Almanac" and "Butterflies of the Northwoods." He lives in Carlton County and teaches natural science at Duluth's Marshall School.

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