Cicadas East, Cicadas West

by Carl Strang

Today’s puzzle is the odd range boundaries of two cicada species that occur in the 22-county area I define as the Chicago region.

The scissor-grinder cicada (Neotibicen pruinosa) is one of the four most abundant annually-appearing cicadas in northeastern Illinois.

Scissor-grinder cicada

Though individuals may sing occasionally from mid-morning to dark, their ee-oo-ee-oo-ee songs especially dominate the wild soundscape at dusk in mid- to late summer. In the following recording, the cicada is introduced and ushered out by a nearby striped ground cricket.

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A recent review of North American cicadas (Sanborn and Phillips 2013, Diversity 5: 166-239) shows what appears to be a gap in the species’ distribution in north central Indiana. I was inclined to regard this as simply indicating a lack of sampling in that area, but this year I pushed to complete my own map for scissor-grinders. Here is the result:

Black dots indicate counties where I have observed scissor-grinder cicadas.

The numbers of scissor-grinders thin out dramatically in the eastern and northern counties of the region. I cannot find them at all in Walworth, Berrien, St. Joseph or Fulton Counties. They barely reach the southwest corner of Marshall County. Sanborn and Phillips show them picking up again farther east, but only one record each for Wisconsin and Michigan, in both cases outside my region.

There is no obvious explanation for the Indiana gap. It does not correspond to soil type, as scissor-grinders can be found in both sand and clay soil areas, and are absent from areas of both.

Swamp cicadas (N. tibicen) have a distribution mainly south and east of the Chicago region, and Sanborn and Phillips (2013) do not map them into the Illinois or Wisconsin portions of my region. My work extends that range a little, but they are scattered individuals in Illinois, with only one Kane County and one Kankakee County site.

Swamp cicada

Black dots indicate counties where I have observed swamp cicadas. Red stars show locations of the northernmost records.

Their song is a percussive vibrato. Here is a recording from southern Indiana in which several individuals provide overlapping songs:

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They occur mainly in the Kankakee and DuPage River areas in Illinois. In the southeastern portion of the region, a few can be found along the Tippecanoe River in Fulton County, but they apparently drop out before that river reaches Pulaski County, which also is well south of the Kankakee River drainage. The swamp cicada’s range boundary is a western one, but explaining it is just as difficult as in the scissor-grinder. St. Joseph County seems to be the center of abundance in the region, with Potato Creek State Park having an especially high density.

The practice of science is largely about questions, and these newly discovered odd range boundaries provide good ones for these two cicada species.

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Ecoblitz Continued

by Carl Strang

The Indiana Forest Alliance, a non-profit conservation organization, has been sponsoring a species survey in portions of two state forests in southern Indiana. As it consists of repeated weekend sessions over a period of years, they are calling it an “ecoblitz” rather than a bioblitz, which is a one-time event limited to a 24- or 48-hour time span. I went down for a weekend last fall, and returned in early August to complete the singing insects portion of the survey.

The area is forested, except for some small areas of tall, dense herbaceous growth in stream bottoms. The singing insect fauna consequently is mainly of forest species.

Confused ground crickets were common on the forest floor.

Confused ground crickets were common on the forest floor.

Say’s trigs by the hundreds sang in the open herbaceous areas.

Say’s trigs by the hundreds sang in the open herbaceous areas.

Widely scattered small groups of rattler round-winged katydids could be heard at night.

Widely scattered small groups of rattler round-winged katydids could be heard at night.

This nymph is recognizable as a male fork-tailed bush katydid by the distinctive appendages at the tip of his abdomen.

This nymph is recognizable as a male fork-tailed bush katydid by the distinctive appendages at the tip of his abdomen.

Some of the other species that sang for us were swamp cicadas, Nebraska coneheads, lesser angle-wing katydids, jumping bush crickets and common true katydids.

I also helped with photography at a night-time moth survey at illuminated sheets.

This small-eyed sphinx was one of the two hummingbird moths we attracted.

This small-eyed sphinx was one of the two hummingbird moths we attracted.

A blinded sphinx also dropped in.

A blinded sphinx also dropped in.

A grape leaffolder

A grape leaffolder

This lesser grapevine looper appears to be sending out pheromone.

This lesser grapevine looper appears to be sending out pheromone.

A Cope’s gray treefrog hopped in, possibly sensing the smorgasbord we had created.

A Cope’s gray treefrog hopped in, possibly sensing the smorgasbord we had created.

 

Return to Berrien

by Carl Strang

Earlier this season I scouted some new sites in Berrien County, Michigan, and on Sunday I returned to see what singing insects I could find in the early portion of the peak season. A first quick stop at Mud Lake Bog produced a hoped-for population of sphagnum ground crickets, and I was reminded how utterly teeny tiny they are.

Most of the day, and a return trip in the evening, went into a place in the eastern part of the county called Chikaming Township Park. If this were Illinois, I wouldn’t expect much from a park district administered at the township level, but this is a good and well maintained site, and it yielded a pile of county records for my study. One of these was provided by a female curve-tailed bush katydid that flew to a landing right in front of me on one of the trails.

The dark-tipped green ovipositor with this shape and proportions, along with the katydid’s overall size and the habitat, permitted the identification.

The dark-tipped green ovipositor with this shape and proportions, along with the katydid’s overall size and the habitat, permitted the identification.

After release, she hung around long enough to let me take a single usable, if not absolutely sharp, photo.

After release, she hung around long enough to let me take a single usable, if not absolutely sharp, photo.

Perhaps the most bizarre observation came as a result of the day’s odd weather. I drove through intermittent rain to get to Berrien County, and waited out the last shower before going out onto the Mud Lake Bog boardwalk. Dark clouds remained until mid-afternoon, but they slowly drifted east and the sun was revealed at 4:00 local (eastern) time. Almost immediately, Chikaming’s swamp cicadas began to sing. These generally are limited to mornings, but here they were going in the late afternoon. This site proved to have the largest concentration I have encountered to date. At one point I wandered into a song battle taking place among a trio of males in a meadow with scattered tree saplings. One allowed a close approach.

None of our other cicadas matches the swamp cicada’s heavy black coloration.

None of our other cicadas matches the swamp cicada’s heavy black coloration.

Later in the evening I was able to pick up some additional species.

Among them was this Forbes’s tree cricket.

Among them was this Forbes’s tree cricket.

The highlight of the day, though, came at another site, Galien River County Park. I had set a goal for this season of listening for spotted ground crickets, which historically have been documented in several Chicago region counties, but which I had not noted to date. Described as a forest species, the spotted ground cricket’s song to my ear is similar to that of a common and widespread species, the Carolina ground cricket. I realized that while some of the forest crickets at Galien River indeed were Carolina ground crickets, others sounded a little different. I made recordings, and listened carefully, and was pleased to conclude that spotted ground crickets were there as well.

An example of a spotted ground cricket location.

An example of a spotted ground cricket location.

The songs have a similar tonal quality and pitch range to my ear. Where the Carolina ground cricket’s song is a steady purr with intervals of added overtones, the spotted ground cricket’s song is composed of regular pulses (about 4 per second), has no overtones, and lacks the continuous steady sound.

 

Return to Cicadas

by Carl Strang

On Monday I returned to the area where I searched for northernmost lyric cicadas, as described two posts ago. I had thought I heard a swamp cicada at Penny Road Pond, and wanted to listen again to confirm it.

Swamp cicada

Swamp cicada

This time two were singing, and there was no doubt I was hearing swamp cicadas’ percussive vibrato. The observation represented a shift well to the north of my previous northernmost location for the species.

The red star indicates the previous location at West Branch Forest Preserve in DuPage County. Penny Road Pond is marked by the yellow star. The two places are around 12 miles apart.

The red star indicates the previous location at West Branch Forest Preserve in DuPage County. Penny Road Pond is marked by the yellow star. The two places are around 12 miles apart.

I don’t know of any place in my 22-county survey region that has abundant swamp cicadas. As the map shows, I haven’t documented them in many counties. In large part that is because they sing only in the morning, and I have done most survey work in the afternoons and evenings when the majority of singing insects are displaying. On the other hand, I went for many long morning bicycle rides in Starke and Marshall Counties, Indiana, and heard only widely scattered individuals. Such a thin spread prevents me from being confident about finding the swamp cicada’s range boundary in the Chicago region.

Back to Monday of this week. I wanted to employ the bicycle as a tool again, this time to see if I could extend the lyric cicada’s northernmost point beyond last week’s record. I started from Trout Park, where I had heard that individual, and dropped down onto a bike trail that took me north along the Fox River. After going 6 miles without hearing a lyric cicada I turned around and headed back. Shortly after making that turn I heard a single lyric cicada, though, giving me a new north point 5 miles beyond the one reported earlier. That was it, however, as I heard no more on the return ride.

Revised lyric cicada map. The new location brings that species’ known range within 2 miles of the McHenry County border.

Revised lyric cicada map. The new location brings that species’ known range within 2 miles of the McHenry County border.

That is as much as I will do this year to determine the possible northward expansion of these two cicadas. I will be interested in pursuing this study in the future, mindful that the thin scatter of both species will lend some uncertainty to the results.

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