The Tiny Ones

by Carl Strang

One of my goals this year was to achieve some clarity with two of the tiniest singing insects in the Chicago region. The variegated ground cricket (Neonemobius variegatus) and Cuban ground cricket (N. cubensis) are only a quarter to a third of an inch long. They are so unobtrusive, with their low-volume trills and hidden haunts, that you have to listen for them even to know they are around. Both species have rapid trills with crescendo starts, and unless you have perfect pitch and better hearing than me, telling their songs apart means working from sound recordings and getting technical.

Variegated ground cricket

Cuban ground cricket

My accumulated recordings of Neonemobius songs fall into two clusters, demarcated by a space that has remained remarkably consistent.

The dots in this graph each represent a recording of a Neonemobius cricket song, analyzed in the computer. The pulses represent the speed at which the cricket rubs his wings together to produce the song, and the frequency is the highness or lowness of the song’s pitch. Both measures increase with temperature. Note that variegated ground cricket songs fall into the upper left portion of the graph, Cuban ground cricket songs lower right. Dashed lines are my eyeball estimates of the space between the two clusters of points.

Variegated ground crickets vibrate their wings more slowly than Cuban ground crickets, yet have higher-pitched songs at a given temperature. This was the tentative conclusion I had drawn, but I needed some validation, and got it in October.

Here I have to back up a bit. I had found variegated ground crickets in the Chicago region, and would not have considered the possibility of Cuban ground crickets without the work of Lisa Rainsong. Cuban ground crickets had been known as a southern species until Lisa found them to be abundant in Cleveland. Her discovery alerted me to the possibility that they also might have reached the Chicago region. That possibility was realized when I found Cuban ground crickets in Gar Creek Forest Preserve in Kankakee County, Illinois. A captive Gar Creek Cuban ground cricket anchored the right-hand portion of the graph (yellow dots, yellow line).

A few observations of variegated ground crickets in previous years fell into the left-hand cluster, but I needed more. This year a captive variegated ground cricket from Gar Creek, which has both species, provided a series of recordings at various temperatures which fell as expected (red dots, red line).

Early in October I visited Lisa and her partner Wendy Partridge, and they showed me an area where Cuban ground crickets are abundant.

This meadow in the North Chagrin Reservation, a Cleveland Metroparks site, is packed with Cuban ground crickets. Lisa and Wendy check out tree crickets down the trail.

My recordings of two individuals at that site fit nicely into the previously established Cuban ground cricket cluster (green dots).

The final touch for 2018 came on October 18. I had 3 recordings, from 2006-2018, from north Blackwell Forest Preserve in DuPage County, all of which fit into the Cuban ground cricket cluster. Despite a few frosty nights, Neonemobius crickets had survived and were singing. I succeeded in flushing out one of these, and he was indeed a Cuban ground cricket. I regard this as a final validation of the graph. Now I need to go back to most of the 22 counties of the Chicago region in future years, and discover where each of these two species occurs.

Revised distribution of variegated ground crickets in the Chicago region, based mainly on analysis of sound recordings.

Revised distribution of Cuban ground crickets. One or both of the two species occur in every county, but I have not yet made sound recordings everywhere I heard Neonemobius crickets singing.

This story is an excellent example of hidden surprises that are waiting for researchers to uncover.

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