by Carl Strang
Most of my field work in the peak month of the singing insects season this year went into pursuing nimble meadow katydids, as described in the previous post, plus going for clarity with two tiny ground crickets. Previously I had learned how to distinguish the songs of Cuban ground crickets and variegated ground crickets, close relatives whose high-pitched trills have weak crescendo beginnings and abrupt endings. That identification requires analysis of recordings in the computer.
Each point represents a different individual’s song. Variegated ground cricket songs (left-hand cluster of points) have slower pulse rates (wing vibration rates) and are higher pitched at a given temperature than the songs of Cuban ground crickets (right-hand cluster).
I knew that both species were widely distributed in the Chicago region, but wanted a more complete picture, so I visited sites in most of the 22 counties in August and September. I made recordings and occasionally succeeded in flushing out crickets for visual identifications.
Variegated ground crickets are smaller than nearly all other ground cricket species, are gray-brown with black lower faces and black backs of their heads.
Cuban ground crickets are slightly smaller than variegated ground crickets and are all black except for their black-tipped white palps.
Cuban ground crickets previously were known only as a southern species until Lisa Rainsong found them in Cleveland and then I found them in the Chicago region. They proved easy to find in all 22 counties.
Map of the Chicago region showing sites where I have found Cuban ground crickets to date.
Variegated ground crickets turned up in every county except Berrien in Michigan, though I had a relatively hard time finding them in the other eastern counties of St. Joseph and Fulton.
Map of sites where I have found variegated ground crickets so far.
Along the way I noted habitat features. Though each species has distinct preferences, there is too much overlap to allow identification on that basis. Cuban ground crickets like open grassy areas such as meadows and prairies. Dry to mesic locations favor them, though on rare occasions I found them in wet habitats. Variegated ground crickets prefer shade, and are more likely to occur where the soil is moist or there are rocks, gravel or patches of bare soil.
Otherwise the only new observation was that Cuban ground cricket songs tended to be shorter, averaging 11.1 seconds to the variegated’s 21.9. The longest Cuban trill was 25.5 seconds, and 30 percent of variegated ground cricket songs were longer than that, up to 104 seconds.
I have a good handle on these two species, I believe, and will be able to concentrate on others in next year’s peak season.
Nature Inquiries 