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.

Seeking Northern Limits: Swamp Cicada

by Carl Strang

The swamp cicada (Tibicen tibicen, the scientific name recently changed from T. chloromera) is another species whose northern range limit is within the 22-county area I am surveying for singing insects.

Swamp cicada. This species is largely black, highlighting the white patches at the anterior end of the abdomen.

Swamp cicada. This species is largely black, highlighting the white patches at the anterior end of the abdomen.

They are present mainly as widely scattered individuals in DuPage County, and sing in the morning. As my survey work this year was taking place mainly in the afternoons and evenings, I hadn’t heard any, and thought I would not. Then, last week, while on the job up at West Branch Forest Preserve, I heard one singing near the lake.

He was in one of these small trees. This habitat resembles an area at Springbrook Prairie near the south boundary of DuPage, the only place in the county where I have heard several swamp cicadas singing at once.

He was in one of these small trees. This habitat resembles an area at Springbrook Prairie near the south boundary of DuPage, the only place in the county where I have heard several swamp cicadas singing at once.

This observation not only is the latest I have heard a swamp cicada singing, it also extends the known northern range boundary.

Swamp cicada observations in DuPage County. The West Branch location establishes the species in the northern half of the county.

Swamp cicada observations in DuPage County. The West Branch location establishes the species in the northern half of the county.

At some point I will need to do more morning survey work in the southern counties of the region, to get a better handle on this species’ abundance and geography.

Learning to Identify Insect Songs

by Carl Strang

One of the obstacles to a singing insect monitoring program is the large number of various songs that need to be learned for identification. This is not really much different from learning bird songs for breeding bird monitoring, however (except that the total number of species is smaller here). Instead of being daunted by the entire process, it is possible to take the learning process in stages, beginning with the songs that are common and easy to recognize, the ones you have been hearing all along but simply didn’t have the species labels. Here is a list of a dozen suggested species to start with in the first stage: spring field cricket/fall field cricket (their songs are identical), Allard’s and striped ground crickets, snowy tree cricket, common true katydid, black-legged meadow katydid, greater angle-wing, round-tipped conehead, dog day cicada, scissor-grinder cicada, and Linne’s cicada (for more information on these species, try the tags at the head of this post).

Snowy tree cricket, one of the species on the starter list

This list and those that will follow are for northeastern Illinois and northwestern Indiana. There would be substitutions in other parts of the country (I encourage readers elsewhere to make comments here with their own suggestions). Go to reference recordings of these species’ songs, either on-line at the Singing Insects of North America website or through the CD that accompanies the Songs of Insects book. It is not too late this year to hear many of the species on this list on the warmer days, though some are finished or nearly so.

My recommended species list to focus on in the second stage of learning consists of 8 species and groups of species: greenstriped grasshopper, gladiator meadow katydid, Roesel’s katydid ( three species that sing relatively early in the season), and then later, Carolina ground cricket, Say’s trig, sword-bearing conehead, two-spotted/narrow-winged tree crickets (no need to worry yet about separating the two), and the meadow tree cricket group (3-4 species whose songs are essentially identical to the ear and will remain so).

Roesel’s katydid is a species from the second-stage list.

This list of common species either will take you to additional, though still readily available, habitats, or else require a little more of a practiced ear (which practice you got with the first species group). In particular, seek out and spend some time getting familiar with the songs of the Carolina ground cricket and Say’s trig. They need a little more effort to recognize in the field, but once you have them, they will be touchstones for many other species (much as robin songs are for learning bird vocalizations). If you are starting now, you might push the Carolina ground cricket to the first list, as it is one of the few species singing on the cooler days and evenings.

Once you have mastered the second list of species, you are ready for the more subtle distinctions needed to distinguish the songs in the third species list. This includes separating out the song of Linne’s cicada from similar songs by the lyric cicada, and in some areas, swamp and/or northern dusk-singing cicada.

Linne’s cicada

Also, by this point you are ready to distinguish the two-spotted tree cricket song from that of the narrow-winged tree cricket. Also, the broad-winged tree cricket should stand out now from other long-trilling species. In addition, you no doubt have noticed and begun to puzzle out other species that are more idiosyncratic in their distribution or smaller in numbers that you have encountered in your favorite places.

And that brings you to the fourth stage, learning the songs of whatever remaining species may live in the area you wish to monitor. For this you will need a regional guide. In the Chicago region, you can meet this need with the guide I am developing. It is available for free as a .pdf e-mail attachment. Simply request it at my work e-mail address: cstrang@dupageforest.com

As you are learning and listening, pay attention to which songs you can hear clearly, and at what distances, and which are marginal. This will inform the limitations you will need to address or acknowledge in your monitoring.

Swamp Cicada Confirmed

by Carl Strang

Two years ago I was positive that I had heard swamp cicadas at Springbrook Prairie Forest Preserve, and posted about it in this blog. The habitat and song were right. However, I had not seen any of them, failed to hear any when I checked the site last year, and doubts developed as I noticed how percussive are some songs of Linne’s cicada, our most common summer species. On Saturday morning I returned to Springbrook for another try (this cicada is mainly a morning singer). I heard a distant cicada that sounded right, and made my way to a pair of small isolated mulberry trees.

They were in a dry location elevated above the stream that was converted from a straight ditch to a proper meandering configuration a few years ago.

I came in too quickly and the cicada flushed, but he simply flew to a new perch higher in the same tree. He resumed singing, and I was able to get a good binoculars view. The swamp cicada, unlike most of our members of genus Tibicen, is physically distinctive. It is largely black, with some green about the head and brilliant white spots on the sides of the abdomen. I was able to confirm the identification, and brought out the camera.

Not the sharpest photo, but sufficient to document the identification.

As singing cicadas often do, he changed his location slightly every few songs.

Here’s a side view. Note that he has lowered his beak.

I was able to get good recordings of the songs, too. I feel confident now that I can identify this species by song. It is based on a pulsing vibrato like that of Linne’s cicada, but is distinctively percussive. Though some individual Linne’s have a hard quality to their vibrations, it is not as sharp, and the sound quality is different. To my ear, the swamp cicada’s song is reminiscent of a rapidly struck tambourine. You can hear an example at the Songs of Insects website.

The significance of this is that the swamp cicada is not supposed to occur this far north in Illinois, though it does so farther east. The swamp cicada joins other species including the broad-winged tree cricket, jumping bush cricket, and round-tipped conehead as singing insects that have extended their range to the north in recent decades. Note: older references give chloromera as the species name for the swamp cicada, but more recent ones have been calling the species Tibicen tibicen.

Meadow Tree Crickets

by Carl Strang

Some tree crickets live in trees, others live among the trees in the forest understory, but there are a few species that inhabit meadow and prairie areas. Last week I looked at some of these when I did some sweep sampling in two locations. The first was Springbrook Prairie Forest Preserve.

This low area dominated by big bluestem grass was part of the habitat I surveyed.

I went there in hope of finding more of the cicadas, tentatively identified as swamp cicadas, that I heard there last year. At the time the song seemed definitive, but I since have learned that Linne’s cicadas sometimes have songs that are similar, and so I was hoping to find one to photograph. All was quiet, however. That’s not necessarily a bad sign. If this is indeed a new population (DuPage is north of the published range for swamp cicadas), they might not be emerging every year. In any case, while I was waiting for singing cicadas I did some sweep sampling, and turned up several tree crickets.

Here is one of the individuals I caught in a goldenrod-dominated area. It has a dark stripe down the top of the head and pronotum, as well as dark antennae. Despite the otherwise pale color, these features point to the black-horned/Forbes’s pair of tree cricket sibling species.

Proper identification of these tree crickets requires an examination of spotting on the basal two antenna segments.

Here the spots on the first, basal segment are very large and smudged. Those on the second segment likewise, to the point where the entire segment looks black at first glance. Also note the dark area on the underside of this tree cricket’s abdomen. All these features point to black-horned/Forbes’s.

The next cricket, from the big bluestem area, is much paler, and shows a different antennal spot pattern.

Here the spots all are smaller, and the outer ones on the basal segments are round and have smeared edges. This is a four-spotted tree cricket.

Another Springbrook tree cricket was more ambiguous.

This individual happily nibbling my finger shows spotting that falls within the range of overlap for four-spotted and black-horned/Forbes’s tree crickets. The most definitive spot is the outer one on the basal segment. It appears just large enough to rule out four-spotted.

The next day I did some sweep sampling at Mayslake Forest Preserve.

The sample included several pale tree crickets like this.

The cricket in that last photo had the following spot pattern.

This is a clear indicator of four-spotted tree cricket, the outer spots on both segments small, round, and faded looking.

A final example showed even fainter spots.

Again I identified this one as a four-spotted tree cricket.

There is a fourth meadow species that I have been watching for but so far have not found. The prairie tree cricket is generally pale, like the four-spotted. Its antenna spots are heavy and close together, but without the blurred smudging of the black-horned/Forbes’s species pair.

August Insect Phenology

by Carl Strang

I was able to accumulate first-of-the-year sightings for 11 insect species at Mayslake Forest Preserve in August that could be compared to last year’s dates. These ranged from 44 days earlier to 77 days later, with a median of 11 days earlier. The extremes in range are greater than I see in plants, and usually reflect either different generations of insects within a season (I missed spotting representatives of an earlier or later generation in one year or the other), or uncommon species.

I also added 13 new species to the preserve’s list. Some of these I have mentioned in earlier posts (straight-lanced meadow katydid, citrine forktail, and fork-tailed bush katydid). Others were the black blister beetle,

meadow fritillary,

common buckeye,

ailanthus webworm,

fiery skipper,

and green cloverworm moth.

The fiery skipper is a southern species that moves north in considerable numbers in some years. The green cloverworm moth is distinctive enough that the blurry photo is sufficient to identify it, a common species whose presence is expected. The remaining new species were eastern tailed-blue, common true katydid, jumping bush cricket, and swamp cicada. As mentioned in an earlier post, I have been alert for the presence of the swamp cicada in DuPage County, and was pleased to hear single individuals singing on three different days at Mayslake in August.

DuPage Swamp Cicadas

by Carl Strang

Not long ago I mentioned that I have begun listening for songs of the swamp cicada, Tibicen chloromera, in DuPage County. Since then I have heard some songs that seemed close, but none that were completely convincing. That changed on Wednesday morning, when I heard unmistakable songs from several individuals of this species at Springbrook Prairie Forest Preserve, in southwest Naperville. The habitat and song perches were just as the literature would lead one to expect: the cicadas were singing from small bur oak trees in a mesic prairie adjacent to a stream. Specifically they were in the Springbrook “remeander” project area.

The photo, taken in 2007, shows the stream shortly after it was converted from a ruler-straight ditch to a stable channel shape with bends, or meanders. Alongside were planted the small bur oaks and a variety of prairie forbs. There is no historical evidence for a natural meandering stream at the site, so it is likely that a sheet-flowing swale, rather than a defined, meandering streambed, preceded the straight ditch. The meanders have the effect of reducing the stream’s steepness, slowing it down so erosion is minimized. Aided by the resulting diverse array of pools and riffles, the stream can support a greater diversity of life. The project rightly has earned several awards for the Forest Preserve District of DuPage County. Two Naperville high schools send Advanced Placement Environmental Science classes to collect data from the project each year, and I was there on Wednesday in connection with that educational dimension.

The cicadas did not sing for a very long time. I wonder if their being closer to the edge of the species’ range explains the more limited habitat variety, song perch choice and singing period I seem to be finding in DuPage County, compared to chloromera I have been observing in the more southern Culver, Indiana, area I referenced in the earlier post. Such thoughts will inform my continued search for swamp cicadas in DuPage.

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