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.

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.

Tibicen Song Sorting

by Carl Strang

My first entry into singing insects study came when I ran across the University of Michigan cicada website in 2003 or 2004. The site includes recordings of cicada songs, and as I played them I realized that all my life I had been hearing the distinguishable songs of several species without knowing it. These were all members of genus Tibicen, and that summer I recognized three common species in DuPage County.

They look very much alike, and are hard to see when singing high up in trees, so it was well that their songs were distinctive. After a couple years, however, I began to notice that the songs I attributed to one of the three, Tibicen linnei or Linne’s cicada, had two variations and with references I was able to distinguish a fourth common species, Tibicen lyricen, the lyric cicada. The differences among these species and their songs I described in some detail in a post last year.

Recently I was reviewing a wide range of singing insects reference recordings when I realized I need to pay attention again to the songs I have been identifying with Linne’s cicada. The swamp cicada, Tibicen chloromera, has a vibrato very close in speed to linnei’s. It has, however, a percussive quality in each vibration that sets it apart from linnei’s smoother, more wavelike vibrato. I had paid too close attention to written descriptions of the swamp cicada, in both the popular and scientific literature, which imply that chloromera is found only in wetlands and sings only from low perches. In fact I am now finding that at least around Culver, Indiana, chloromera often sings hundreds of yards from wetlands, and at least as often from high trees as from perches in lower ones. I have heard them in forests as well as more open stands. This is in keeping with other Tibicen cicadas, which at least in their singing perches show wide ranges in habitat.

So far I have not heard chloromera in DuPage County. I have found that I need to listen carefully, because when lyricen are singing their first, warmup songs of the day they have a slower vibrato with a percussive quality like chloromera’s.

The two areas I frequent most, DuPage County, Illinois, and Marshall County, Indiana, have different Tibicen species lists though they are only about 100 miles apart. Both are homes for canicularis, linnei, lyricen and pruinosa (the dog day, Linne’s, lyric and scissor-grinder cicadas, respectively). So far, only Marshall County appears to have chloromera, the swamp cicada, but I don’t consider the case to be closed. Marshall County also has a sixth species, Tibicen auletes, the northern dusk-singing cicada, which is associated with sandy soils and so does not occur in DuPage County’s clays.

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