White River Crayfish Young

by Carl Strang

This week brings the end to another year’s running of amphibian traps in the stream corridor marsh at Mayslake Forest Preserve. As was the case last year, I have caught relatively few amphibians compared to the number of invertebrates. This year the majority of captures have been, specifically, white river crayfish (a species of marshes and other still waters in flood plains adjacent to streams).

A mature white river crayfish is impressive in its red coloration.

Last year I caught only adults. This year brought all sizes, and I was able to get a sense of how they change with age (my reference gave only verbal descriptions). Young ones have small pincers, and are an olive color with distinctive black spots on the sides.

Immature white river crayfish, around 1.5 inches long.

As they get bigger the spots fade, the pincers get a little bigger, but the color remains olive.

This one is around 3 inches long.

I keep watching for some variation that might hint at a young grassland crayfish among the white river ones, but so far none have turned up.

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