Making a Case 3: Northern Wood Cricket

by Carl Strang

Last year I concluded that I had found northern wood crickets (Gryllus vernalis) in the Winamac State Fish & Wildlife Area in Pulaski County on June 13, based on habitat and sound recordings. In 2016 I returned to that site on May 29, but did not find them singing. On June 3 I heard Gryllus crickets chirping along the Marquette Trail, near the east border of Lake County, Indiana. All were in forest or savanna areas, the singers in deeply layered black oak leaves, usually in shade under black oak trees but some in isolated collections of leaves surrounded by sand.

One of the woodland crickets’ song sites near the Marquette Trail.

One of the woodland crickets’ song sites near the Marquette Trail.

None were in the open grassy areas favored by spring field crickets (G. veletis), even though such habitat was close by. I recorded two of these individuals, and later in the season recorded field crickets in meadow and prairie habitats favored by veletis but where vernalis would not be expected, plus another individual that by habitat should be vernalis, at the Kankakee Sands site in Kankakee County, Illinois.

The results seemed contrary to what would be expected from previous studies.

The likely vernalis (forest) had lower chirp rates than likely veletis (grassland).

The likely vernalis (forest) had lower chirp rates than likely veletis (grassland).

The number of pulses per chirp was unhelpful, with likely veletis ranging 2-4, likely vernalis 3-4. Linear regressions of the two sets of data show, perhaps significantly, the same slopes of chirp rate increase with temperature (physiology of closely related species expected to show a similar response to temperature). The linear regressions indicate that, for a given temperature, forest cricket chirp rates are 1.44/second less than grassland chirp rates. All data I can find in the literature for vernalis were collected from that part of their range where they are sympatric with the southern wood cricket (G. fultoni). Jang and Gerhardt (2005. J. Evol. Biol. 19:459–472) found that fultoni song characteristics differed between populations sympatric with vernalis and those allopatric to that species. They did not study allopatric vernalis. As my recordings may be the only ones that have been made where vernalis is allopatric to fultoni, and given the clear difference between recordings in habitats for likely vernalis and likely veletis described above, so far it appears that habitat, chirp rates and temperatures will be enough to establish the presence of vernalis. The major obstacle to finalizing this conclusion is confirming the identity of the forest crickets. So far I have been unsuccessful in efforts to catch or even see one. Next year I need to continue making recordings and trying to catch and measure suspected northern wood crickets.

Recent Travels: Places

by Carl Strang

I have fallen behind on blog posts. The season is heating up, and I have kept busy doing various surveys in various places. Today’s start on catching up will focus on some scenes and miscellaneous photos taken along the way.

The Marquette Trail at Indiana Dunes National Lakeshore passes beautiful marsh and sand savanna habitats.

The Marquette Trail at Indiana Dunes National Lakeshore passes beautiful marsh and sand savanna habitats.

I found northern wood crickets singing along the trail. They bury themselves in leaf litter like this.

I found northern wood crickets singing along the trail. They bury themselves in leaf litter like this.

Another example of a wood cricket song site. I tried to get a look at one, but they choose deeply stacked litter areas with plenty of hidey holes and escape routes.

Another example of a wood cricket song site. I tried to get a look at one, but they choose deeply stacked litter areas with plenty of hidey holes and escape routes.

Painted turtles wandered the savanna seeking good places to lay their eggs.

Painted turtles wandered the savanna seeking good places to lay their eggs.

Another good sand area is Illinois Beach State Park. Here a trail goes through the zone behind the fore dunes.

Another good sand area is Illinois Beach State Park. Here a trail goes through the zone behind the fore dunes.

Farther back from the edge of Lake Michigan, black oak savanna lines the trail.

Farther back from the edge of Lake Michigan, black oak savanna lines the trail.

Though my main interest was singing insects, there were many four-spotted skimmers to enjoy at IBSP.

Though my main interest was singing insects, there were many four-spotted skimmers to enjoy at IBSP.

I also have spent some time in Kendall County. This plains clubtail was at Hoover Forest Preserve.

I also have spent some time in Kendall County. This plains clubtail was at Hoover Forest Preserve.

This year’s Indiana Academy of Sciences bioblitz was at Goose Pond in southern Indiana. I stopped on the way down for a walk at Turkey Run State Park. Ravines there provide many scenes like this.

This year’s Indiana Academy of Sciences bioblitz was at Goose Pond in southern Indiana. I stopped on the way down for a walk at Turkey Run State Park. Ravines there provide many scenes like this.

I didn’t end up taking any scenery shots at Goose Pond. As I was setting up the UV light, I found this mama spider crossing the road, her back covered with babies. All their eyes glittered like jewels in the headlamp.

I didn’t end up taking any scenery shots at Goose Pond. As I was setting up the UV light, I found this mama spider crossing the road, her back covered with babies. All their eyes glittered like jewels in the headlamp.

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