Landscape Ecology of Singing Insects 1: Glacial Influences

by Carl Strang

One of my winter projects has been to write new sections for my singing insects guide which go into ecological topics. This was inspired by my reading a newly published textbook on landscape ecology (With, Kimberly A. 2019. Essentials of landscape ecology. Oxford University Press, Oxford, U.K. 641 pp). In the next few posts I will share parts of the added sections. Today’s focus is the impact of the last continental glacier on the landscape and selected insect species:

Though the focus in most of this guide is on the individual species of singing insects, the field of landscape ecology provides a framework of broader patterns and questions for which the ecologically diverse singing insects provide a suitable lens.

Landscape ecology considers geographical patterns and dynamics of their change across time. Any complete biological understanding of the Chicago region must include not only what is here now but also how it got that way. Fortunately, we don’t have to go back too far geologically speaking, as our landscape is less than 20,000 years old. Three major lobes of the most recent continental glacier flowed down from the North and scoured our region’s bedrock, then began their final retreat around 18,000 years ago. As the glacier melted, with occasional periods of stalling when the push from the North was balanced by melting at the edge, it left behind a variably deep layer of various kinds of deposits. The topography was more elevated in the morainal arcs where the melt was stalled for a time, lower and flatter when the melt-back was more uniform and rapid. Occasional pocks formed where blocks of glacial ice were buried and later melted, resulting in small lakes, bogs and other wetlands. Our rivers had their start as glacial meltwater drainage streams. The Lake Michigan Lobe of the glacier picked up and crushed the softer shale from the bottom of what was to become that lake, so it left behind deposits heavy in clay west and southwest of the lake. When glacial crunching and meltwater eroded harder igneous and metamorphic rocks the ice had transported from Canada, gravel and sand resulted. Quartz sand, the most erosion-resistant component of such rocks, accumulated especially around the edge of Lake Michigan and the tributaries of the Kankakee River, which started as a glacial meltwater drainage stream originating in the part of the region covered by the glacier’s Saginaw Lobe.

This glacial history impacted our singing insect fauna in various ways. Some species require, or at least are only abundant, on sandy soils. These include the green-winged and northern dusk-singing cicadas, whose nymphs live on buried plant roots, and some of the grasshoppers, for which the sandy substrate for egg-laying and/or a poor-soil plant community is an important habitat component. A couple of species, the gray ground cricket and the seaside grasshopper, are limited to the beaches and dunes around the Lake Michigan edge.

The beaches at different points on the Lake Michigan shore have different compositions, resulting in selection for different colors in the seaside grasshopper. Here, at Illinois Beach State Park, there is a greater mix of different colors of ground igneous and metamorphic rocks.

The beaches of the Indiana Dunes are a more uniform quartz sand. Here, two seaside grasshoppers (same species as in the previous picture) would be nearly invisible if they were not flashing their inner femur colors at one another.

Kames are gravel hills formed by waterfalls within the melting glacier, and they provide a well-drained substrate. Isolated populations of sulfur-winged grasshoppers and tinkling ground crickets live on a kame in the Lulu Lake Nature Preserve in northern Walworth County, Wisconsin.

Exposed gravel on part of the kame at Lulu Lake.

All species were pushed south by the glacier, surviving in what is now the southern U.S. and being influenced by selective forces then and during the advance north as the climate moderated and plant communities spread back over the barren glacial deposits. Most of our familiar prairie and forest plant species were restricted to rather small refuges in the South during the glacial maximum, though oaks and hickories occupied a large part of the southern U.S.

Black oak savanna, Kankakee County

As the glacier melted back, open sedge tundra with some black spruce trees invaded first, then white spruces filled in to form a recognizable northern coniferous forest until around 15,000 years ago. By around 12,000 years ago most of our landscape was a mix of deciduous species, including woodlands with lots of oaks. Beginning around 10,000 years ago there was a drying period, which led to the spread of prairie through our area. The prairie then retreated as the climate became wetter, so that by 6200 years ago the western part of our region was a prairie with islands of woodlands and wetlands, grading to forest in the eastern part. This reflects a gradient of increasing moisture from west to east, mediated by the flow of wet air circulating north from the Gulf of Mexico. The drier prairies were maintained by fires which frequently knocked back woody plants that otherwise would have converted even the western part of the region into woodlands. The wooded islands within the prairie were not randomly located, but survived where rivers, other wetlands, and topographic breaks shielded certain spots from prairie fires pushed by the prevailing westerly winds. The upshot for our singing insects is a diverse landscape that to this day contains species specializing in prairie, woodland and various wetland habitats, as well as some that thrive around the edges between habitat types. A few species may be relicts of earlier changes in this history. For instance, the delicate meadow katydid, now apparently extinct in the region, is abundant in prairies to the west and probably accompanied the prairie advance. By the early 20th Century it was known in a very few scattered locations. I have not been able to find it anywhere in the present day.

Delicate meadow katydid females have longer ovipositors than their close relatives.

Small Wonders at Illinois Beach

by Carl Strang

Two targets for my friends from Ohio and West Virginia were stripe-faced meadow katydids and gray ground crickets, both of which can be found at Illinois Beach State Park. The stripe-faceds proved to be in their early-stage colors.

Even this nymph has the facial stripe, but it is brown and relatively fuzzy-edged compared to what it ultimately will become. New adults have the same brown colors, even though they are mature enough to sing and to mate.

Even this nymph has the facial stripe, but it is brown and relatively fuzzy-edged compared to what it ultimately will become. New adults have the same brown colors, even though they are mature enough to sing and to mate.

The nymphs and new adults were all in shades of tan and brown. We saw one or two adults which were beginning to develop their green body colors, and the more distinct facial features.

The nymphs and new adults were all in shades of tan and brown. We saw one or two adults which were beginning to develop their green body colors, and the more distinct facial features.

Gray ground crickets have been a challenge, and prior to this year I had gotten only a couple brief glimpses of them. This time I caught one, allowing us to take photos before releasing our subject back into the dunes.

The cricket was a female, probably made vulnerable by her moving about seeking a singing male.

The cricket was a female, probably made vulnerable by her moving about seeking a singing male.

Gray ground crickets are well named. I especially like the head stripes and the little dark rectangular markings on the wings.

Gray ground crickets are well named. I especially like the head stripes and the little dark rectangular markings on the wings.

We found other critters of interest along the way, of course.

Kiowa rangeland grasshoppers occupy the same ecological zone as the gray ground cricket.

Kiowa rangeland grasshoppers occupy the same ecological zone as the gray ground cricket.

Scattered cottonwood trees among the dunes were hosts for this striking beetle, a cottonwood borer.

Scattered cottonwood trees among the dunes were hosts for this striking beetle, a cottonwood borer.

The loudest nighttime insect singer was the robust conehead. We saw both brown and green males.

The loudest nighttime insect singer was the robust conehead. We saw both brown and green males.


Sometimes It Gets Messy

by Carl Strang

I haven’t been posting here lately, as I have been busy writing summaries and reports on the past season of my singing insects study. As 2014 was a good, productive year, this has been a time consuming process. The discovery of variegated ground crickets in October brought a new complication, as their song superficially resembles those of several other crickets, including Say’s trig and a few other ground crickets. I decided to review all of my relevant recordings and re-analyze them to discover distinguishing features. Two quantities that researchers have discovered to be significant in singing insects are dominant frequency (pitch or highness of the tone) and pulse rate (the speed at which wings open and close to produce the song). These are determined by sonographic analysis of the recordings in the computer. The plot of all the recordings looks like this:

Hence “messy” in this post’s title.

Hence “messy” in this post’s title.

The colors represent my decision as to species (usually I did not see the singer): red for Say’s trig, green for variegated ground cricket, blue for gray ground cricket, black for sphagnum ground cricket, and yellow for Cuban ground cricket. The shapes represent one of three ways in which these crickets begin their songs: square for an abrupt start (or for unknowns, cases in which the recording did not include the start of a trill), triangle for a crescendo from low volume to the extended peak of loudness, and circle for a start that often is rendered “chuwee.” The last has an abrupt beginning, but immediately has a momentary drop in pitch or volume that as quickly is followed by the continuous, full volume trill. All these crickets end their trills abruptly. Empty centered shapes are for recordings that were noisy or in which more than one individual was singing, potentially leading to a false reading. The numbers are the temperatures in degrees Fahrenheit, when known.

Ideally, there would be well defined clusters of points separating the represented species. This did not happen, and I can identify a few reasons. In some cases, the recording’s quality was compromised (the hollow-centered shapes). Temperature can affect song qualities, and there is no single established threshold for all species, below which recordings become ambiguous. Also, some features of songs are not in the graph, notably the length of trills, and the length of pauses between them.

The outlier for variegated ground crickets, the green triangle with the lower frequency and pulse rate, was the recording I made indoors. I only kept that cricket for one night, and had it in a cage with only a few leaves on its floor. I have more trust in the values for the Cuban ground cricket, which was well established in a beautifully furnished terrarium at Lisa Rainsong’s home in the Cleveland suburbs, where I stopped briefly on my way to my brother’s for Thanksgiving (thanks again, Lisa!).

Here are my tentative conclusions from this analysis:

First, I need to make a lot more recordings, with care to note habitat, temperature, and whether the singer is on the ground or height above the ground. I need to isolate one singer from all others, with the microphone as close to it as possible. Better habitat conditions are needed to get good response for indoor recordings.

So far, dominant frequency, habitat, and how the trill starts are more helpful than pulse rate in distinguishing these species.

Say’s trig songs are characterized by a chuwee start, a location above the ground, and a lower pitch (usually 7.5kHz or less). Trills may be long or short, but when short usually are in rhythmic bouts.

Variegated ground crickets consistently have crescendo starts, trills usually less than a minute long, and pauses between of at least several seconds. Field recordings had high dominant frequencies (8.6 kHz or above).

One Cuban ground cricket recorded indoors had a pattern like that of the variegated, but a lower dominant frequency (7.6 kHz). From Lisa’s description, these two species occur in very similar habitats, but the Cuban ground cricket is more likely to be found on the surface of the ground. Variegateds occupy soil cracks or other buried locations.

Gray ground crickets have abrupt starts and only brief-moment pauses, with dominant frequencies of 8.0-8.9 kHz. They occur in dry sand soils.

One recording of a sphagnum ground cricket has a high dominant frequency (8.5 kHz), plus a chuwee start. It occurs only in sphagnum bogs, but potential associates include Say’s trig and variegated ground cricket, which can be distinguished, respectively, by their lower dominant frequency and crescendo starts.

That’s enough for now. I plan to share some of these recordings in future posts.

Sound Ideas: Gray Ground Cricket

by Carl Strang

In the vegetation that grows just behind the beaches around the western Great Lakes you may hear a very rapid, high-pitched trilling sound, as in this recording I made at Whitefish Point (on the north side of the tip of Michigan’s Upper Peninsula) on September 16, 2009:

The area where the previous recording was made.

The area where the previous recording was made.

This interrupted trill is identical to the reference recording for the gray ground cricket on the Singing Insects of North America website. Indeed, this species is expected in open, sandy soil habitats. The only other ground cricket song I have heard that is close to this is that of the sphagnum ground cricket, which is restricted to sphagnum bogs and could not survive on sand. Allard’s ground cricket, when it occurs with the gray ground cricket, has a distinctly slower song.

The challenge for me with this species has been two-fold. First, I have never seen one. Second, I am pretty sure they occur inland as well. Here is a recording from Braidwood Dunes, a Will County Forest Preserve, September 7, 2011:

At the time I noted that there were pauses, but enough crickets were singing simultaneously that these are difficult to pick out in the recording. I have heard, and sometimes recorded, this same song in other inland locations in Kendall, Marshall and Fulton Counties. Sometimes the pauses are infrequent or nearly absent, but the songs all have a peak frequency of 8-8.5 kHz, and share similar patterns of amplitude irregularity in their sonographs. I am not aware of any other cricket that could occur in dry soils with a song like this. Furthermore, there are some mentions of inland gray ground crickets in the literature, and some authors refer to the trill as continuous. So, mainly by process of elimination I have decided to refer to all these crickets as gray ground crickets for now, but with a higher priority of catching one, particularly at one of the inland sites, for confirmation.

Return to Illinois Beach

by Carl Strang

A return to Illinois Beach State Park was called for last week, as my first visit was early enough in the season that more singing insects could have become active since. For instance, gray ground crickets were not singing yet in early August, but by last week they were active.

Gray ground crickets are common in the scattered clumps of grasses and other plants behind the Great Lakes beaches.

Hearing is not seeing, however, and despite my best efforts I could not expose a gray ground cricket for a photograph. They were in the larger patches of vegetation and trapped oak leaves, and it was too easy for them to sneak away when I tried lifting leaves and plant stems to look for the hidden singers. That disappointment was relieved somewhat by an amusing dung beetle.

It was having difficulty moving this far-from-spherical chunk.

I had better luck with grasshoppers. Some members of the grasshopper subfamily Oedipodinae are in the park. These qualify as singing insects, as their displays include wing-rattling flights. I found two species. One, a darker form, was in the savanna near the Dead River.

This appears to be a Boll’s grasshopper, a relatively dark individual of the species. The yellow and black hind wings are hidden when folded at rest.

The beach was another grasshopper habitat.

Some grasshoppers prefer this more open vegetation structure.

A common species was pale and well camouflaged.

This one appears to be a seaside grasshopper.

In the night, I followed a tree cricket’s song as it trilled in the gray ground cricket habitat.

The antenna spots don’t show here, but they clearly revealed that this was a four-spotted tree cricket.

Robust coneheads had become common in the campground woods.

This male sings from a patch of big bluestem grass within the savanna.

I found a few more species to add to the site list, but none were particularly uncommon.

Indiana Dunes State Park Mystery

by Carl Strang

Indiana Dunes State Park is an older preserve than the National Lakeshore that surrounds it. Last week I spent a day there searching for singing insects. As was true at the National Lakeshore earlier in the month, most of the species I found were familiar, but there were a few added ones. For instance, a female rattler round-wing katydid was climbing the outside wall of the park’s nature center.

Later in the evening I heard a couple males singing nearby.

Also that evening I heard a number of jumping bush crickets. The dunes area had, as expected, gray ground crickets.

The day also brought a mystery. As had been the case at the National Lakeshore forest, confused ground crickets were common in the shaded areas, and there were a few tinkling ground crickets around the dry edges. In addition, however, in the wet-mesic forest south of the State Park’s great marsh, and extending well into the wooded margins of the marsh, a common third species was singing a clear and steady trill. It was similar in pattern, but distinctly lower in pitch and with a different tonal quality, than the Say’s trigs that were abundant in more open areas nearby.

Red oaks, ferns and deep leaf litter were characteristic of the mystery cricket’s song sites.

I remembered that the spotted ground cricket is a forest species I had not yet found, and thought that perhaps this would prove to be the solution. Later, however, when I consulted reference recordings, I was reminded that the spotted ground cricket has a pulsing trill unlike the mystery cricket’s steady song. Reviewing other possibilities, I hit upon the melodious ground cricket. The song was very close to what I heard.

The melodious ground cricket is not as well known as many other ground crickets. Edward S. Thomas and Richard Alexander first described it in 1957, and their work provides much of what has been published about it, at least in the North. They characterized it as a marsh species, but their more detailed site descriptions often, if not usually, place it among woody plants. “The majority of our specimens of melodius were secured by tearing apart a soggy, decayed log, honey-combed with insect burrows, about 20 feet from the marsh proper.” While this supports my tentative identification, at some point I will need to get back there and catch some of these crickets to make a positive determination.

Braidwood Dunes etc.

by Carl Strang

Last week I traveled to southern Will County to seek singing insects in sand country. My main stop was the Braidwood Dunes Natural Area, managed by the Forest Preserve District of Will County. I only got into part of it, and what I saw was outstanding.

There was an extensive dry prairie on sand soil dominated by little bluestem, for instance.

That prairie hosted the largest concentration of common meadow katydids I have encountered to date. In DuPage County I have found only scattered individuals and tiny groups.

It was a windy day, and the katydids were very shy. I took maybe 20 photos to get a couple that were only slightly blurry.

One of the species I specifically was seeking was the gray ground cricket. In places that were very similar in vegetation and soil to those where I heard this species at Illinois Beach State Park, I heard trills that sounded the same in memory.

One of the places where I heard probable gray ground crickets.

I made a recording, and cannot distinguish the sound, in trill speed or tonal quality or pitch, from that in a recording I made at Whitefish Dunes in the U.P. of Michigan a couple years ago (where the only candidate is gray ground cricket). Having no permit, I was not about to try and capture, let alone collect, specimens, so comparisons of recordings will have to do for now.

Otherwise, I heard mainly common species at Braidwood Dunes. I was happy to discover long-spurred meadow katydids in a wooded area, and I also made an observation that at first seemed trivial but later proved more substantive. It seemed that the Allard’s ground crickets were slowing their trill by a huge amount in shaded areas under trees. By the time I made the day’s final stop at Forsythe Woods Forest Preserve, I had realized that the slow ones might have been tinkling ground crickets, a sibling species of Allard’s. I made a recording of one there, and it proved identical in tonal quality and pitch, and in fact had a slightly longer spacing between notes, than the confirmed recording of a tinkling ground cricket by Lang Elliott and Wil Hershberger. This experience highlighted the emphasis here and there in the literature that the tinkling ground cricket is a species mainly of dry woodland edges.

My other stops were along the Kankakee River in my continuing search for variegated ground crickets.

I stopped first at a place with a long sandy river edge.

No ground crickets in the sand.

I also found a stretch with a significant pebbly shore.

The only ground cricket here was a single Carolina ground cricket. That’s it for seeking variegateds this year. Next year I may try for them in areas where they apparently are more concentrated, in southern Indiana. Once I have experience with the species, I may have a better idea of where to look in northeast Illinois.

Sphagnum Ground Cricket

by Carl Strang

The sphagnum ground cricket was a species I had sought but failed to find in DuPage County last year. Apparently low vernal pool areas in our woodlands are not sufficiently close to the sphagnum habitat the species requires, and as we have no sphagnum in DuPage I would need to look elsewhere. When my plans for Illinois Beach State Park were thwarted by the south unit’s closure, I decided to move on from the north unit (where I had been successful in my search for gray ground crickets) to Volo Bog State Natural Area.

This is the center of the main bog, accessible by a well maintained boardwalk.

The outermost zone of the bog was not promising. There was no sphagnum that I could see, mainly marsh plants, with the prominent singing insects being black-legged meadow katydids and Carolina ground crickets.

Here is the marsh habitat, with the next, shrubby zone in the background.

As I entered the next concentric ring of habitat, working my way toward the bog’s center, a mix of shrubs was dominant. The black-legs and Carolinas petered out. I began to see sphagnum moss.

The shrub and sphagnum habitat at Volo Bog.

At first I heard mainly Say’s trigs, but it seemed there was something else. I got out the SongFinder, and its frequency-lowering function allowed me to identify a second, fainter, more rapid trill. When I then removed the headphones I found that I could pick out the second trill, which matched my memory of reference recordings of sphagnum ground crickets. I got down on my hands and knees at the edge of the  boardwalk, probing the sphagnum lightly with my fingers, and that was all it took to get some photo ops.

This nymph was the first sphagnum ground cricket I saw. I was struck by its beautiful coloration, especially the mottling and white dots on the hind legs.

Adults seemed mainly black.

The mottling is subdued on the legs, but still present on this adult. The eyes are large and brown.

There were so many singing at once that I was not able to pick out the ends of any trills. The song seems very like that of the gray ground cricket, but fainter, being a very rapid, level, high-pitched trill (more rapid than those of Allard’s ground crickets or Say’s trigs). I am guessing that the gray ground cricket needs to be louder in its more open, wind-swept dune habitat.

Gray Ground Cricket

by Carl Strang

The south unit of Illinois Beach State Park is closed. I found that out when I arrived there, having taken a vacation day and driven the hour and a half or so it takes to reach Zion. That squelched singing insect research Plan A, though it turned out for the best, as we’ll see. I would not be able to achieve all my goals, but I could at least try to find gray ground crickets at the north unit.

Grassy area just inland from the beach at Illinois Beach State Park’s north unit.

Between the parking lot and Lake Michigan, this grassy area is protected enough from wind and waves to support tall prairie grasses including big and little bluestem, and Indian grass, as well as a few forbs. The soil appears to be nearly pure sand. All I was hearing at the parking lot were some fall field crickets and Allard’s ground crickets, but I followed a path toward the beach and soon, in the sandy prairie shown in the photo, was hearing scattered gray ground crickets. I kept hoping I might see one out on the path, but no such luck, and I didn’t want to be too intrusive at an area that already gets much use. I’ll hope for a photo opportunity some other time.

The gray ground cricket’s song is distinctive, though in part that is because of the connection to the habitat. There was one place where an Allard’s was singing close enough to a gray to allow a direct comparison. Both ground crickets have long trills, but that of Allard’s is noticeably slower, the individual notes fully distinguishable if a little too rapid to count. The gray ground cricket’s trill is much more rapid, though still audibly composed of distinct notes (i.e. they don’t blend into a single tone). The song is higher pitched than that of Allard’s. In addition, the gray incorporates characteristic pauses here and there. A recording can be found on-line here.

It was only mid-day, so I decided to check another Lake County site on my fall research list, which I had thought would have to happen on another day. I’ll report on that tomorrow.

Singing Insects at Whitefish Point

by Carl Strang

The third goal of my Upper Peninsula trip last week was to study the singing insects there. Compared to northern Illinois, the singing insect fauna was very limited. At night the campground at Tahquamenon Falls State Park was quiet, except for the amazing snoring of one of my neighbors, thankfully only for one night. During the day the principal singing insect in the forest was the dog-day cicada.

Open areas such as Whitefish Point had more to offer. I was especially pleased to find that gray ground crickets are common there. Like all ground crickets these stayed well hidden. Here is typical habitat.

Gray ground cricket habitat b

This species is known from dunes areas around southern Lake Michigan, but the only time I was at Illinois Beach State Park listening for them was a windy day and I could not hear them clearly. At Whitefish Point I easily distinguished their song. Though the trills seem composed of discrete notes like those of Allard’s ground cricket, they are at least three times faster (Allard’s were there as well, making comparison easy). Also, the trills were not continuous but rather were interrupted by brief pauses that were spaced regularly in some individuals but at varying intervals in others. In addition to Allard’s, familiar crickets at Whitefish Point were fall field crickets and Carolina ground crickets.

Whitefish Point also was home to two singing grasshoppers that represented the two forms of grasshopper song production. One of them was a crepitating species like Illinois’ greenstriped grasshopper. My references point to the clearwinged grasshopper, Camnula pellucida, as the identification, though I am not certain.

Clearwinged grasshopper 2b

In the photo the male is on the left. Crepitation is sound production by the rattling or snapping of the wings in flight. In this species the rattle is much louder than that of the greenstriped grasshopper. Clearwinged grasshoppers occupied the more open dunes areas. The other form of sound production is called stridulation. A common grasshopper that stayed close to woody plants at Whitefish Point produced loud “zuzz-zuzz-zuzz” sounds with this method. My best stab at identification is Thomas’s broad-winged grasshopper, Chloealtis abdominalis.

Thomas's broad-winged grasshopper 3b

The black areas on the sides of the pronotum seem to point to that species. Another photo, taken just as the grasshopper turned to put some distance between itself and my camera, shows that from behind the legs have a lot of red on them.

Thomas's broad-winged grasshopper 5b

In stridulation, both legs are lifted and lowered at once, and rows of pegs on them rub against the folded wings to produce the sound.

I also found broad-winged bush katydids at Whitefish Point, but I will hold that discussion for a later time.

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