by Carl Strang
An emerging theme of my field season this year is defining range boundaries of the singing insects I am studying. When there is a boundary within my 22-county study area, usually the population density thins out toward the edge. That has me looking critically at some of my past observations. A case in point is the confused ground cricket (Eunemobius confusus).
Confused ground cricket. These are little guys, a quarter of an inch long.
Looking at past records, I found that only two were north of the midpoints of Kane, DuPage and Cook Counties in Illinois. There was a single individual in the Lyons Prairie and Marsh area, legally within Lake County, Illinois, though managed by the McHenry County Conservation District. I had noted a small group of the crickets in the New Munster Wildlife Area in Kenosha County, Wisconsin. Now several years on without other records for those counties, I felt the need for a double check. I visited both sites and found no confused ground crickets. I did, however, hear other singing insects that I now believe fooled me.
Here is a recording of a confused ground cricket. This guy was singing in cool temperatures, and so was slowed somewhat:
Usually the song would be faster, with trills or chirps about a second long, alternating with equal-duration spaces within which the cricket produces stuttering sounds. The Lake County and Kenosha County observations both were made well into long days in the field, and my fatigue along with relative inexperience years ago, led me to mistakes. I now believe that the Lake County observation in fact was a Say’s trig, producing an uncommon alternative song composed of brief trills with the same timing as a confused ground cricket. Here is an example of that song:
You may notice there are occasional stutters between the trills. On my return visit to the New Munster site, I did not hear any confused ground crickets, but I noticed that there were a lot of black-legged meadow katydids singing in dry habitats, unusual and unexpected in that species. Furthermore, in the heat they were singing so fast that their buzzes were about a second long, with the ticks compressed in such a way that they resembled a confused ground cricket’s stutters. Here is a black-leg recording with similar timing:
These conclusions support my practice of making lists of the species I hear on each visit to each site. That makes the oddities stand out, helping me to correct errors like the ones I have described here. I now can close the book on confused ground crickets, with the final map:
Black dots indicate counties where I have found confused ground crickets. The red stars mark locations of the northernmost observations within Kane, DuPage, Cook and Berrien Counties.
Nature Inquiries 