Sweep Sampling

by Carl Strang

There are two groups of singing insect species about which my knowledge is most lacking. First there are the ground crickets, which are audible but have songs that often are similar, and they are difficult to catch for the purpose of identification. And then there are the small meadow katydids, whose songs are so high pitched that I can no longer hear them, or are so soft that they are overpowered by the many other louder species around them. Thanks to the SongFinder I have found two of these, the short-winged meadow katydid and the slender meadow katydid. Last week I employed another technique in this search: the sweep net.

A sweep net is like a butterfly net, but the bag is made of a heavy close-woven fabric that withstands being swept back and forth through vegetation. I started my search in the stream corridor prairie at Mayslake Forest Preserve. I tried taking 25-sweep samples in various parts of that prairie. The first interesting insect I caught was this one.

I released this bird-dropping-mimic butterfly caterpillar after photographing it. I thought it looked familiar, but never had seen one live. Later I found that it was a viceroy butterfly larva, which is almost identical to that of the red-spotted purple. The two species are very closely related, being in the same genus, but selection has pushed adult color development in two entirely different directions. The sweep sampling session added one new species to the preserve list.

This is a citrine forktail. Several fell into the net, but they are so well camouflaged and so still on their perches that I had not noticed any before. The singing insects I caught belonged to familiar species. Here is a female short-winged meadow katydid.

I also caught a tree cricket. This was a more typical example of the black-horned/Forbes’s species pair than the individual I described in a post a few days ago.

Though pale on the back, it was dark beneath the abdomen, and the antennal spotting was unambiguous.

Those spots are large, dark, and smudged together.

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1 Comment

  1. August 25, 2010 at 6:40 am

    […] I described sweep sampling. The day after I tried out the technique in the stream corridor prairie, I shifted to Mayslake’s […]


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