Stream Sampling 2

by Carl Strang

Today I’ll continue the inventory of animal life found in Mayslake Forest Preserve’s tiny stream, focusing on the insects. Among the first to turn up, farthest downstream from the stream’s origin at May’s Lake, were a couple species of beetles. One was, at first glance, the size and shape of a whirligig beetle, but a closer look proved otherwise.

This is a strong underwater swimmer, with threadlike antennae.

Its features were by now familiar thanks to my recent experience with a larger member of its family in the nearby marsh. This is a predaceous diving beetle. There is a pale marking at the posterior edge of its elytron that bends inward over the surface, probably distinctive but not matching anything in my reference. Without a more distinctive photo or specimen I’ll have to be content with the family. I had better luck with the other beetle.

This little guy belongs to a different family, the Haliplidae, known as the crawling water beetles. I wouldn’t have named them that, because they swam pretty well in the tray, but I understand that in their habitat they mainly crawl over the bottom and vegetation. They are primarily vegetarians. They look very much alike, but if I’m reading the details correctly, this one is Peltodytes duodecimpunctatus. That is a ridiculously long name for an insect only 3-4 millimeters long.

I was pleased to pick up a caddis fly larva in the sample. Many members of this insect order build distinctive protective cases that they carry with them.


According to one of my references, the fact that this larva built its case out of roughly rectangular pieces of dead leaves places it in family Lepidostomatidae. These live as detritivores, consuming dead leaves. That underscores a significant aspect of stream ecology. There is so much edge, relative to the volume of the stream itself, that the stream’s economy and physical features are strongly influenced by, and dependent upon, the adjacent terrestrial environment.

Two kinds of damselfly larvae appeared in the sample. Both appear to belong to the pond damsel group.

The overall shape, and the trio of gills at the tip of the abdomen, are distinctive to these little predators.  

The final insect species showed up very close to the May’s Lake outlet; I caught two. These were worm-like, and 1-2 inches long.

Guess which is the head end.

The ring of tentacles around the tail end, and other features, place these in the crane fly family. Tipulidae is the only family for crane flies but it is huge, and I don’t know where I would begin for an identification. I like crane flies, though, the adults with their gangling long legs. Most larvae are, like the caddisfly, decomposers in their ecological role.

After all of this I still have an assortment of half a dozen organisms to cover, in one final chapter to close this series tomorrow.



  1. Marie said,

    April 21, 2011 at 1:03 pm

    It was with joy that I read about a stream sampling by someone who loves exploring the tiny stream dependents as much as I do.

  2. jomegat said,

    April 21, 2011 at 5:06 pm

    Whenever I find an interesting bug I can’t identify, I post it on – if it’s a good enough photo, that usually results in a good outcome.

    • natureinquiries said,

      April 22, 2011 at 5:55 am

      Thanks, JT,
      I tried posting something there once and got no response whatsoever. Perhaps I should try again some time.

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