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.

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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.

Northern Wood Crickets

by Carl Strang

Those of you on the mailing list for my annually updated guide to the singing insects of the Chicago region would look in vain for northern wood crickets in last year’s edition. I simply wasn’t aware that they could be here. While preparing for the Hills of Gold bioblitz, however, I found that their range extends into our region. I had not included them in the hypothetical list because initially it was directed toward DuPage County in Illinois, and wood crickets never have been found in northeastern Illinois. I gained some experience with wood crickets in the bioblitz, and the sound recordings I made there proved to be of the northern wood cricket, Gryllus vernalis. Study of the relevant scientific paper (Yikweon Jang and H. Carl Gerhardt. 2006. Divergence in the callling songs between sympatric and allopatric populations of the southern wood cricket Gryllus fultoni [Orthoptera: Gryllidae]. J. Evol. Biol. 19: 459–472) indicated that the 2-chirp-per-second, 3-pulse-per-chirp, songs coming from leaf litter in forest habitat, were of northern wood crickets. Southern wood crickets, the other possibility, would have had faster chirps at that temperature.

Last week’s vacation survey trips went so well, despite two days lost to rain, that I had Saturday available to seek northern wood crickets the Indiana portion of the Chicago region (I had not found them in the Illinois, Wisconsin or Michigan excursions). My first two stops, in St. Joseph County’s Bendix Woods and Fulton County’s Judy Burton Nature Preserve, were fruitless. Mid-afternoon brought me to the Winamac State Fish and Wildlife Area in Pulaski County, and I drove the gravel roads until I found one of the parking lots in a forested spot. Immediately I heard the chirps of Gryllus crickets, and I dug out the Marantz sound recorder. As I recorded two different crickets I believed I was hearing 3 pulses in the chirps, as had been the case at the bioblitz.

This was where the cricket in the recording shared below was located.

This was where the cricket in the recording shared below was located.

I would have liked to try and flush out one of the singers, but as the photoflash lighting in the photo suggests, it was getting dark fast, and I barely reached the car before the downpour hit. I tried to get around the storm by driving to the Jasper-Pulaski Fish and Wildlife area, but no dice, and I had to call it a day. So, here is a cut of the stronger recording:

Can you distinguish the 3 pulses that form each chirp?

The visual rendition of the recording clearly shows the 3-pulse chirps, but they are being produced at a 4-chirp-per-second rate.

The visual rendition of the recording clearly shows the 3-pulse chirps, but they are being produced at a 4-chirp-per-second rate.

This might have been confusing, given that the southern wood cricket, not yet known from northern Indiana, more typically has a 4-chirp rate, but the soil temperature was very warm, at nearly 80F, and the scatter for vernalis in Jang and Gerhardt’s graph extends to 4 chirps at that temperature. Also, the dominant frequency was 5.9kHz, good for vernalis but pitched way too high for fultoni at any temperature. So, I am content for now that I have established a present-day northern wood cricket presence in the region. One goal for next year will be to seek them in more locations, make more recordings, and get a better sense of their song features in this part of their range.

Hills of Gold

by Carl Strang

This year’s chapter in the bioblitz series organized by the Indiana Academy of Science was called Hills of Gold. It was on a beautiful site being assembled by the Central Indiana Land Trust, and when complete will occupy around 2 square miles in Johnson County, south of Indianapolis.

The event took place on an intermittently rainy day, as illustrated by this less than sharp image of a representative bit of forest and one of the old logging trails we used to get around the site.

The event took place on an intermittently rainy day, as illustrated by this less than sharp image of a representative bit of forest and one of the old logging trails we used to get around the site.

Usually my role in these bioblitzes is to survey singing insects, but this was too early in the season for a sufficient number of species to justify my participating. I decided to reconnect with my experience studying forest Lepidoptera ecology in the 1980’s, and took on moths as well. As I walked the forest during the day, I found many beautiful plants and animals outside my target groups that gave joy.

Green dragons always make me smile, and I ran across a magnificent cluster of them along one of the streams.

Green dragons always make me smile, and I ran across a magnificent cluster of them along one of the streams.

And who can say “no” to fire pinks? Hummingbirds sure don’t.

And who can say “no” to fire pinks? Hummingbirds sure don’t.

Violet wood sorrel is a plant I haven’t encountered very often.

Violet wood sorrel is a plant I haven’t encountered very often.

There also were insects to note outside my target groups.

This Bombus impatiens queen still had not found a nest site, and was prospecting the forest floor.

This Bombus impatiens queen still had not found a nest site, and was prospecting the forest floor.

I interrupted this female scorpionfly’s feed on an emptied caterpillar skin.

I interrupted this female scorpionfly’s feed on an emptied caterpillar skin.

Speaking of caterpillars, the first target species I found was this eastern tent caterpillar:

They already had reached the final instar and were starting to pupate.

They already had reached the final instar and were starting to pupate.

I collected only four moth species during the day. All were fairly common.

This was one of them, which I identify as the unadorned carpet, a member of the inchworm family.

This was one of them, which I identify as the unadorned carpet, a member of the inchworm family.

Many more moths came to my ultraviolet light setup that night. Stay tuned for that episode.

For the record, there was one singing insect. This was my first encounter with a wood cricket. I heard them scattered thinly all through the forest, but never succeeded in seeing one. They probably were northern wood crickets (Gryllus vernalis), but might have been southern wood crickets (G. fultoni). I made a couple good sound recordings, which I hope will allow me to make the determination.

One of them was singing from this patch of leaf litter.

One of them was singing from this patch of leaf litter.

More on that later, after I have analyzed the recordings.

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