Tree Cricket Clarity

by Carl Strang

A year ago I was struggling with the identification of a group of four meadow-dwelling tree cricket species that reportedly live in northeast Illinois and northwest Indiana. They have been determined to be close relatives, and two of them had been established as sibling species by Thomas Walker of the University of Florida: the black-horned tree cricket and Forbes’s tree cricket are physically alike, and can be distinguished only by the pulse rate of their songs, which requires the analysis of sound recordings.

Forbes’s and black-horned tree crickets can be very black, as shown in this individual at Pinhook Bog in Indiana.

Forbes’s and black-horned tree crickets can be very black, as shown in this individual at Pinhook Bog in Indiana.

This is a paler representative of the species pair from the Great Marsh, also in the Indiana Dunes National Lakeshore.

This is a paler representative of the species pair from the Great Marsh, also in the Indiana Dunes National Lakeshore.

One member of this species group, the four-spotted tree cricket, is readily identified. It is pale, and has a distinctive pattern of spots on the basal segments of its antennae.

All four of the spots on the two lowest antenna segments of this four-spotted tree cricket in Fulton County, Indiana, are relatively small and well separated. The outer spot on the basal segment is nearly round.

All four of the spots on the two lowest antenna segments of this four-spotted tree cricket in Fulton County, Indiana, are relatively small and well separated. The outer spot on the basal segment is nearly round.

The final species is the prairie tree cricket. I thought I found this species last year at Mayslake Forest Preserve, again following the long-established focus on antenna spot patterns.

This individual was generally quite pale, and the antenna spots matched reference drawings for the prairie tree cricket.

This individual was generally quite pale, and the antenna spots matched reference drawings for the prairie tree cricket.

When I analyzed my sound recordings of the songs of prairie/black-horned/Forbes’s tree crickets from Mayslake and other DuPage County locations, however, they generally fell out as Forbes’s, though some recordings made at lower temperatures were somewhat ambiguous.

This confusion has been largely resolved, now, thanks to the recently completed Ph.D. thesis work of Laurel Symes. She traveled widely in her study of these species, collecting specimens and analyzing their songs and their genetic relationships. Though her focus was on female response to male songs, and the associated behavioral, ecological and evolutionary implications, the information she collected also is very helpful to my regional survey of singing insects.

Though she doesn’t say this herself in anything I have seen, it seems clear that we need to throw the time-honored focus on antenna spot patterns out the window for three of the four species, though it still holds for the four-spotted tree cricket. Laurel found a geographic separation between black-horned and Forbes’s tree crickets, with a zone of contact that may involve some hybridization. That zone is in Ohio, safely east of the Chicago region. Unless something new emerges in the future, I am following Nancy Collins in calling all our local ones Forbes’s tree crickets as a result of Laurel’s research.

As for the prairie tree cricket, it, too, seems not to be in the region, occurring well south and west of us. I will retain it on the hypothetical list, though, because Laurel’s results were less certain on this point.  In any case, as long as the temperature is warm (at least 68F), the remaining three species can be distinguished from sound recordings, so they need not be captured. All you need is the temperature, the graphs relating pulse rate to temperature, and a pulse rate count from the recording. At the standard temperature of 25C, four-spotted tree crickets have a pulse rate of 40 per second, prairie tree crickets 51 per second, and Forbes’s tree crickets 65 per second. Laurel found that selective pressures on male song and female choice keep these quite separate and narrowly defined, .

Song Analysis

by Carl Strang

One of my goals this autumn was to begin sorting out the meadow dwelling tree crickets of the nigricornis species group at Mayslake Forest Preserve. In earlier posts I shared some photos that pointed to a mix of species, but now I have studied their songs, and the results prove to be complicated. One individual was straightforward. He was unique in having an abdomen that was black beneath.

I immobilized him briefly in the freezer for photos.

I immobilized him briefly in the freezer for photos.

His antennal spots clearly distinguished him as either a black-horned tree cricket or a Forbes’s tree cricket.

There was clear separation between the spots on the second antenna segment, and those spots were narrow.

There was clear separation between the spots on the second antenna segment, and those spots were narrow.

When I looked at my recording of his song in the Audacity sound analysis program (available as a free download), the pulse rate clearly was that of a black-horned tree cricket.

The program allows the pulse rate to be counted, in this instance the interval between the 6-second and 6.5-second point in the recording. The pulse rate of 36-37 per second at 65.5F is unambiguously that of a black-horned.

The program allows the pulse rate to be counted, in this instance the interval between the 6-second and 6.5-second point in the recording. The pulse rate of 36-37 per second at 65.5F is unambiguously that of a black-horned.

The other tree crickets were problematic. Here is the most ambiguous case. His antenna spots, along with his generally pale coloration, said he was a prairie tree cricket.

The spots on the second antenna segment were thick, and had a very narrow space between them.

The spots on the second antenna segment were thick, and had a very narrow space between them.

On the other hand, his song had a very rapid pulse rate.

A pulse rate of 48 at 68F is close to that of a Forbes’s tree cricket.

A pulse rate of 48 at 68F is close to that of a Forbes’s tree cricket.

All the other tree crickets I tested had songs most like Forbes’s, but only one had the antenna spots to match. The others either were closer to those of the prairie tree cricket, or were ambiguous. The literature I have seen cannot carry me any farther. My next step will be to look at nigricornis-group tree crickets at other sites in 2013, and hope for enlightenment.

Black-horned Subtleties

by Carl Strang

Lately most of the members of the nigricornis group of tree crickets I have been catching at Mayslake Forest Preserve have proved to be prairie tree crickets. Last week I found an exception that brought out some of the subtle distinctions among these insects.

The broad black band on the underside of the abdomen narrowed this one down to being either a black-horned or a Forbes’s tree cricket.

The tips of the legs and antennae likewise were black. However, he was pale on top.

There was a diffuse darker stripe down the top of the head and pronotum, but so pale as to be ambiguous.

With this group of species it is a good idea always to look at the antenna spots. In this one the spots on the basal segment were large, fused and fairly well defined.

The spots on the second segment were very narrow, however, and well separated, as they should be in this species pair.

Another lesson I learned from this cricket was the importance of viewing angle on those second-segment spots. You need to look straight down on the inner spot with respect to its own position, rather than from the cricket’s mid-line, which gives only a slightly tangential view of the critical spot. After taking the photos I took the cricket home and he sang for me, so later the recording should allow me to determine which of the two sibling species he was.

Prairie Tree Cricket

by Carl Strang

Recently I shared the story of a tree cricket that I suspected may be a prairie tree cricket. Last week I caught a second one which confirmed the identification, at least as far as I can tell.

As before, I put him in the freezer for a few minutes to immobilize him for photos.

Like the first, he was pale, and his extremities were brown rather than the black of a black-horned or Forbes’s tree cricket.

Beneath, he was dusky on the underside of the abdomen, but not black.

The critical feature is the spotting on the first two antenna segments.

In this one there was none of the smudging that fuzzed one edge of one of the spots on the first cricket. The spots on the first segment were large and fused. The spots on the second segment also were thick.

I was concerned that the pixilation in the photos might be distorting the appearance of spacing between the spots on the second segment, so I took the added step of examining them through the magnifying glass. The spaces were indeed being exaggerated by the camera. This further supports the case for prairie tree cricket.

So now I have the impression that all four species in the nigricornis group of meadow-dwelling tree crickets are present (I have found the four-spotted tree cricket in a few locations), and all may be common, in northeast Illinois. The prairie tree cricket, once a western species, has spread east thanks to agricultural practice. After catching the subject of this post I have had a devil of a time trying to get more (they seem to be staying close to the ground for warmth), so I may not make more progress in quantifying the relative numbers of the species this year. Unfortunately the pulse rates of prairie and black-horned tree cricket songs are nearly identical across the range of temperatures in which they sing. Otherwise I could do the survey entirely with recordings. The four-spotted seems to prefer grasses, but song perches for the other three are goldenrods, asters and even woody plants, so there is little to distinguish them in habitat preference. As for monitoring practice, it looks like this will simply have to be a category “nigricornis group” rather than a count of the separate species.

A Cricket’s Adventure

by Carl Strang

At mid-day on Friday, a tree cricket sang from a Canada goldenrod plant near the eastern edge of Mayslake Forest Preserve.

The central character in today’s story.

At this point in the season, the long-trilling meadow-dwelling tree crickets are mainly members of the sibling species pair of black-horned tree cricket and Forbes’s tree cricket. The two species cannot be distinguished except through an analysis of their recorded songs. The critical feature of the song, the pulse rate, varies with temperature, and in the field the temperature can vary significantly with microsite at this time of year. So, I caught him and installed him in a cage. Back home, in the quiet of the evening, he began to sing and I got my recording.

The next day I wanted good photos for documentary purposes. I put the cricket in a jar, and the jar in the freezer for 10 minutes. This immobilized the little guy long enough for me to get photos.

The dorsal view shows that this individual is very pale. The antennae and tarsi are dark, but not the black typical of the two species. There is no stripe on the pronotum.

There is some dusky pigmentation on the underside of the abdomen, but this too can be much darker in black-horned/Forbes’s tree crickets. He looks dead, but he fully revived within 15 minutes or so.

The spots on the first two antennal segments are very helpful in tree cricket characterization. Here the spots are large, dark and close together.

The cricket’s adventure was nearly complete. I had a public night hike Saturday night, and I took him in a jar, releasing him with an explanation of his story and the reason I put him through it.

It was only later, when I studied the photos closely, that I began to have some doubts. The heavy, close-together markings correspond more closely to those of a third species, the prairie tree cricket, which I had been seeking but not found. The literature and on-line information seem to suggest that, nevertheless, this could be a black-horned/Forbes’s. The critical question seems to be, how wide is the space between the two bars on the second antennal segment? If it is less than a third the width of the inner bar, then this is a prairie tree cricket. If more, it’s a black-horned/Forbes’s. As best I can tell, it is very close to this critical width. I will continue to pursue the question for this individual, but all of these species show some variability, and my best response is to find more crickets in Mayslake’s meadows, and see what they tell me.

Return to Houghton Lake

by Carl Strang

With the singing insect season winding down, I made a final trip of the year to Houghton Lake in north central Indiana. I had not been able to reach certain wetlands on my previous visit, but with much of my strength recovered I was able to wade through the tall dense vegetation.

The periphery of the wetland area was of good quality. There were many interspersed shrubs.

Farther in the center, the portion I explored quaked like a bog, but there was no sphagnum and I imagine it is more calcareous, over marl, and thus more fen-like. The plants were senescing, and I found no singing insects of interest in there, but it will be worth exploring earlier in a wetter year.

One highlight of the trip was a pair of black-horned or Forbes’s tree crickets I found engaged in courtship. My attention was drawn by the unusual buzzing quality of the male’s singing, which he produced whenever the female backed away.

Most of the time I watched them, she was feeding from the glands on his back at the base of his wings.

The male was relatively small and pale. The female was larger, and the darkest individual of this species pair I have seen.

Her head was black, and she had liberal amounts of black pigment on the rest of her body and legs.

These species remain active well into October, and I have wondered if the dark pigmentation is an adaptation for the late season.

Toward Singing Insect Monitoring: Wall of Sound

by Carl Strang

A few days ago I began addressing the challenges to developing a monitoring protocol for singing insects. The biggest single difficulty is, as I described, differences in peoples’ ability to hear different pitches of sounds. Frogs and birds, the other organisms monitored by their songs, vocalize well within the hearing range of most people. Not so with singing insects.

It takes time to learn to recognize the various songs, but a learning period is part of every monitoring program. Also, monitoring will need to be done day and night because different species sing at different times. Apart from these relatively straightforward aspects, there are at least two other difficulties to overcome that are peculiar to singing insects. One of these is the lack of a vocabulary for describing insect songs. This will come with time, as different people come up with creative ways to communicate. For instance, several times I have heard people likening the tick-and-buzz pattern of the generic meadow katydid song to the sound of a sprinkler set to bounce back rhythmically to its cyclic starting point every few seconds.

Carolina ground cricket, one of the contributors to the wall of sound (though not this particular female, of course).

The final challenge is what I call the wall of sound. This is especially true at night, when the greater number of species and especially of individuals all are singing at once. In particular, many of the common tree crickets and ground crickets have more or less continuous trilling songs that blend to produce a collective mass sound that seems largely undifferentiated. I have a solution that works for me, and perhaps it could be made part of a protocol. When I do my block counts at night, I count only those individual singers that are close enough for me to distinguish clearly as I walk along. I ignore the wall of sound at large. For the most part this gives me a good sample of the species producing that wall, along with the others whose songs are more easily distinguished.

Singing black-horned/Forbes’s tree cricket, another element of the wall.

This isn’t a neat and perfect solution, however. Some of the long-trilling tree crickets have songs that cannot be separated from one another by ear. Others, and I am thinking here specifically of Davis’s tree cricket in my area, usually sing high enough in the trees that their songs are completely buried. Individuals can be distinguished only on the rare occasions when their song perches are low in the canopy (in such cases the Davis’s song is low enough in pitch to stand out).

As should be clear by now, if a singing insects monitoring program is to be comprehensive, it can’t be based on point counts, as is the case in breeding bird surveys and frog monitoring. It will have to be based on a route, as in dragonfly or butterfly monitoring. In conclusion, I think the elements are in hand to produce a workable protocol for a singing insects monitoring program. The main thing missing is enough people sufficiently interested that they will put in the time to learn the songs. Tomorrow I’ll suggest a learning program that will help people to learn insect songs in readily digestible stages.

Chain O’Lakes

by Carl Strang

Last week I spent a day and night at Chain O’Lakes State Park, near the Wisconsin border in Illinois. There are extensive wetlands in that park as well as dry upland areas. Though my singing insect search for the most part turned up common, expected species, I have hope for better results in a future wetter year. In the extensive upland restored prairie areas Allard’s ground crickets were the main daytime singers. In a lower, damper, goldenrod-dominated patch were some black-horned tree crickets (or, possibly, their sibling species the Forbes’s tree cricket).

The heavy but well separated basal spots on the antennae plus the dark antennal color identify this as a black-horned.

In a higher-quality prairie patch not far from some trees I found a bush katydid.

The species cannot be determined from this angle.

A quick capture made for an easy identification.

The brown, curved ovipositor distinguishes the female fork-tailed bush katydid.

Later, after dark, I heard a number of sword-bearing coneheads in the prairie areas.

This species, with its distinctive sewing-machine song, is common in meadows and prairies of the region.

Wetlands are abundant at this park, and some appear to be relatively high in quality.

Pike Marsh

The singing insects were of common species for the most part.

The slender meadow katydid is abundant in wet places.

The most conservative species I found at Chain O’Lakes was a female long-tailed meadow katydid.

This was the first green-legged female of this species I have seen. Usually they are all brown.

I will return to that park in a wetter year.

Kankakee Sands Bioblitz

by Carl Strang

For 24 hours on Friday and Saturday, over 100 field biologists convened at the Kankakee Sands area in Newton County, Indiana, for a bioblitz. The area includes Nature Conservancy prairie and savanna restoration sites and Indiana state nature preserves. The bioblitz, a concentrated effort to identify as many species of organisms as possible, was sponsored by the Nature Conservancy, Purdue University, The Indiana Academy of Science, and a consortium of Indiana colleges.

Check-in on Friday afternoon.

Though the bioblitz focuses on the central 24 hours, some advance work had been done.

For instance, a team of Purdue entomologists had begun collecting beetles the previous day.

My focus was singing insects. One of the Purdue students volunteered to assist me the first afternoon.

Alyssa Collins, a junior majoring in entomology, sports an entomological hitchhiker/hat.

Alyssa’s young ears were a huge help with some of the meadow katydids, which I cannot hear without an electronic aid.

For instance, she found this long-spurred meadow katydid, which proved to be a common species in the savannas.

I was prepared to collect extensively if necessary, but fortunately for my preferences we only needed to collect as we saw fit. I collected only 3 insects altogether. The long-spurred wasn’t one of them.

The song and habitat were sufficient for identification, but it doesn’t hurt to take advantage of photo opportunities. Here the male’s cerci show why this is named the long-spurred meadow katydid.

The timing was a little early for many of the singing insects. Meadow-dwelling tree crickets still were nymphs.

This one still is an instar or two short of maturity.

They generally were consistent with the black-horned/Forbes’s tree cricket species pair, but I will need to return in some future season to explore further.

Antennal spots which, if they hold to this arrangement after the final molt, will confirm my tentative ID.

We were able to spend some time in savanna and prairie areas.

Conrad Savanna, an Indiana state nature preserve.

Area L, one of the Nature Conservancy’s Kankakee Sands Efroymson Family Prairie Restorations.

In the next few posts I’ll share more from the bioblitz.

Tree Cricket Nymphs

by Carl Strang

While sweeping for meadow katydid nymphs last week I also picked up a few immature tree crickets. I took the time to photograph some of them.

This example, just a few millimeters long, has no wing pads yet.

After consulting Nancy Collins’ excellent tree cricket site, I think this one is in its third instar, 3 molts short of adulthood. Other information on her site suggests, from the pattern of fine white dashes on the abdomen and lack of a striping pattern, that this might be a black-horned tree cricket, which is common at Mayslake Forest Preserve. It took some maneuvering to get a reasonably clear photo of the spots on the first two antenna segments.

Eventually, a Kilroy-was-here shot achieved the goal.

These spots are valuable in identifying adult tree crickets, but I don’t know whether they are useful in nymphs. This pattern certainly fits the black-horned/Forbes’s tree cricket species pair (cf. diagram at the Singing Insects of North America website).

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