Field Crickets

by Carl Strang

When I started my study of singing insects, I already was familiar with field crickets, the common black chirpers whose song most people find pleasant (you can find recordings here or here). As I reviewed the literature I was surprised to find that there are two species of them in our part of the country, the spring field cricket and the fall field cricket. These are what biologists call sibling species. They are practically identical in almost every respect, and yet they do not interbreed and so are separate species.

Spring field cricket 2b

Both are black, the same size and shape, and have indistinguishable songs. The songs, by the way, as in all the singing insects, are produced by the males. The females follow the songs to find mates. What distinguishes the spring and fall species apparently is their season. Spring field crickets mature early. In previous years I have noted first songs on 28 May 2006, 12 May 2007, and 31 May 2008. This year I heard a few in Marshall County, Indiana, on May 16, and one in DuPage County, Illinois, on May 18. In July their singing tails off as they complete their breeding, lay their eggs, and die. There doesn’t seem to be a completely song-free gap, though singers are very few in the middle of July. By the end of that month the number of field cricket songs is increasing rapidly, and we have entered the reproductive season for the fall field cricket. That season extends into the fall. The last song dates I have noted were 20 October 2006, 17 October 2007, and 4 November 2008. Very few are to be heard by October, however.

Spring field cricket eggs hatch early enough for them to begin growing in the late summer and fall. Fall field cricket eggs reportedly wait until spring to hatch. Each species has a 1-year lifespan, but they are offset as I have described.

Field crickets sing day and night, though I have not yet measured whether there are variations in how much they sing at different times. They don’t always occur together. For instance, I have never heard a spring field cricket in my home neighborhood, nor have I found any at Fullersburg Woods Forest Preserve, though I have heard fall field crickets in both locations. Both spring and fall field crickets are common; I have found each species at 21 northeast Illinois locations (mainly DuPage County) so far, though both species occurred together at only 13 locations. Both occur in woodlands and meadows, but the spring species seldom ventures into lawns as the fall field cricket does. Both also are comfortable around human structures.

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