New Trap Critters

by Carl Strang

One way of assessing the biodiversity of an area is by the rate at which new species are added to the area’s list with sampling effort. There are ways of doing this quantitatively, but in my amphibian trap sampling of the stream corridor marsh at Mayslake Forest Preserve I am (so far) just getting a qualitative sense of what is there. My sampling has been limited to just a few tens of trap-days last season and this. Still, the traps continue to produce new finds, including three species last week.

It must have taken some effort for this 3-inch bullfrog to squeeze into the trap.

Two leopard frogs were in another trap. I didn’t take a photo. I also caught a few water bugs.

They all have been this size (less than an inch long), and they have the shape of giant water bugs.

One of them proved to be an adult male, with eggs attached to his back.

The males carry the eggs, keeping them clean and oxygenated.

There are 3 genera of giant water bugs in the eastern U.S. The ones I had heard of, the ones famous for attacking tadpoles, fishes and other vertebrates, have a significantly larger body size at maturity. The second genus, with only one species in the eastern U.S., was easily ruled out. That left genus Belostoma. I was not able to determine the species from the photos.

I keep records of all individuals caught in the traps. At some point I will be able to chart number of species added against number of individuals caught, and number of species added against trap-days, to get a more quantitative sense of the marsh’s biodiversity. As long as I am catching new species this frequently, though, it makes sense to wait.

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