Landscape Ecology of Singing Insects 3: Changes Over Time

by Carl Strang

Some of the formalism developed by landscape ecologists clarifies the current status of our singing insects and their prospects for survival. From the standpoint of a given species, the landscape is viewed as patches of habitat imbedded within a matrix of non-habitat. If that matrix is hostile to the species, the habitat edge is a “hard boundary,” and unless the species is good at dispersing long distances, they will be confined to their habitat island. To different degrees that extreme may not be met if there are steppingstones or corridors that can act as acceptable temporary refuges for dispersing individuals. I suspect that such is the case with pine tree crickets, for example. These habitat specialists are common in conifer groves across the region, many of which seem too isolated for such a small, specialized insect to cross the intervening distances. Nancy Collins, a Wisconsin specialist on the subfamily, has noticed that pine tree cricket nymphs can live, at least temporarily, in non-conifer, herbaceous habitats. Edges of conifer groves thus are not hard boundaries for pine tree crickets. In other cases, river corridors and highway rights-of-way can serve as travel lanes. Thus, the little-known dispersal abilities of our various species are key to understanding their status.

Pine tree cricket

In some of the crickets and katydids which normally are short-winged and flightless, long-winged morphs occasionally appear. Roesel’s katydid, mentioned in the previous post, essentially is never long-winged in its native Europe, but commonly is so here, where the species is expanding its range. There is a tradeoff in play for such species. Long-winged variants are good dispersers, but their fecundity is reduced.

Roesel’s katydid, long-winged variant

Dispersal also can be facilitated by humans. I have seen examples, with Japanese burrowing crickets and jumping bush crickets, of individuals and small groups showing up far ahead of the front of their range expansion, in places where landscape materials are stored or sold.

Mate finding motivates some movement by singing insects. The females in general must travel to meet up with singing males. The males themselves also may need to change their position. In DuPage County, where swamp cicadas are relatively few and scattered, I have observed males frequently changing position between songs by tens of meters at a time. An Iowa study (Shaw, Bitzer and North 1982) found that sword-bearing coneheads shifted position an average of 6.2m between nights, but otherwise remained associated with their group of other males.

Swamp cicada

The singing insects whose habitat needs are met by landscape alterations for agriculture and residential areas are the abundant, widespread ones. They are easily picked out by the large number of sites marked on their maps in my singing insects guide. Dispersal is relatively easy for them as there are large habitat blocks well connected by amenable corridors. Even they can suffer local extinction as land is cleared of vegetation for buildings or roadways. As new vegetation grows into such places, the weedy species are quick to re-establish themselves, but this underlines the dynamism of the habitat patch mosaic.

Of greater interest, and greater concern, are those species whose needs are not met by human-created habitats. Here the habitat patches are only a small percentage of the landscape, and elements of patch size, patch isolation, and insect dispersal ability become critical to understanding. Theory suggests that when a habitat falls below 10-20% of the landscape, dispersal ability is expected to drop dramatically in the absence of viable corridors or steppingstones; such is certainly the case for many of our habitat specialists. A few species anecdotally are good dispersers. I have reports, or have seen myself, instances of slender meadow katydids and long-tailed meadow katydids showing up in locations remote from their respective habitats. These individuals were unusual among the small meadow katydids in being long-winged morphs; most cannot fly.

Slender meadow katydid

Patch isolation in some cases is such that successful dispersal is impossible. Distances among the few surviving sphagnum bogs, for example, are too great to be crossed by sphagnum ground crickets. Prairie cicadas can fly, but apparently are disinclined to do so far enough to matter. At one of their sites, the West Chicago Prairie in DuPage County, they remain confined to one area of mixed grasses and forbs. They have not crossed the 350 meters of grasses, small shrubs and wetlands that separate them from a similar area within the same preserve. So far, their populations have persisted in remnant prairies ranging from 1 to a few acres. Can such small populations survive long term?

Prairie cicada

That question raises another concept from landscape ecology: extinction debt. This is the idea that a species’ habitat may have been so reduced that it still may be present but is doomed to fade away to extinction because its numbers are inadequate to maintain reproductive viability. Such may or may not be the case for prairie cicadas. I suspect this is what happened to northern wood crickets (NWC) in the region. NWC were known from two forested areas in northern Indiana at the beginning of the 20th Century (Blatchley 1903). One of these was in Marshall County. Years ago I used the original survey notes and county soil map to reconstruct the presettlement landscape of the township in question.

Presettlement map of Union Township, Marshall County, Indiana. Mesic forest was the large green area east of Lake Maxinkuckee.

Blatchley found NWC in the area of mesic forest which, in 1834, was very large. By the end of the 19th century agricultural clearing would have been well under way, and today only a tiny portion of that forest remains, the rest having been converted to pasture and crops. The same is true of forested areas in Lake County, Indiana, the other area where NWC lived in the late 1800’s. Though fragments of the forests where Blatchley found NWC remain, the crickets are gone, and I have checked all the other relatively large forests in the region without finding them. This raises the disturbing question: how many other species presently in the Chicago region are in a state of extinction debt? Patch size needed to maintain a species is dependent upon the characteristics of the species, its population dynamics, and patch quality. These are unknowns for all the uncommon species.

Our two species are Linnaeus’s 17-year cicada, on the left, and Cassin’s 17-year cicada, on the right

I will close this section with a case study on the periodical cicadas in DuPage County. In pre-settlement times the county was, from the cicadas’ perspective, a matrix of prairies and wetlands with 18 forested areas of various sizes scattered throughout. Historical maps and aerial photos allowed me to trace changes in those forests from the early 19th Century to the present day. I measured the forest sizes, noting their smallest (bottleneck) extents and how those were reflected in the presence of periodical cicada choruses in the 2007 emergence. There was a clear threshold of local extinction: forests which had remained above 61ha (hectares) still had cicadas, those which had fallen below 52ha did not, even when they had grown larger subsequently. Old newspaper accounts placed cicadas in at least some of these. Three forests which fell between those sizes appeared to have been affected by isolation, a remote one lacking cicadas, and two near persisting populations having them. The human history peculiar to the county is important here. DuPage County is immediately west of Chicago. The western half of the county quickly became agricultural, with forests cut back to make room for fields and pastures. Forests lacking cicadas in 2007 were mainly in the west. The eastern half developed residential commuter communities, with forests being protected and expanded as people planted trees around their homes. The largest area with cicada choruses in 2007 was lobular in shape, the various lobes following the routes of commuter-serving railways and the towns that expanded along them, connecting several of the pre-settlement forest locations. When the cicada choruses reached their peak in the first half of June, numbers of the insects suddenly appeared in flight, crossing over highways and other hostile environments. Subsequently, small groups showed up in places remote from the concentration areas. Whether these will result in significant expansion of the species in the county remains to be seen, but this observation supports the notion that competition and population pressure produce responses by the cicadas. They have the advantages of stronger flight capabilities and better vision than other singing insect groups.

A Pause in the Action

by Carl A. Strang

In the early part of the season, from April to early July, my research focus is on those species of singing insects which matured from overwintering nymphs, plus some small early-season cicadas. This is a minority of species, as most of the crickets, katydids, and singing grasshoppers mature after the middle of July, having wintered as relatively secure eggs and needing time to grow up.

I was able to close the book on northern wood crickets last month, and the story here is a sad one. This forest-dwelling member of the field cricket group had been reported from two northern Indiana sites by W.S. Blatchley in 1903. As far as I know, no one has sought them since then in the northern part of the state. Last year I determined that they no longer occur where Blatchley found them. This year I checked the largest other eight forests in the Indiana portion of my study region. If they ever were there, they are gone now. I suspect that forest fragmentation for agriculture and other purposes is responsible for the loss. Blatchley’s detailed descriptions leave no doubt that he knew how to recognize the species.

This northern wood cricket is from the northernmost site where I know they still occur, Eagle Creek Park in Indianapolis.

I was able to close the book on another southern species, the spring trig, in June.

This tiny, early-season cricket is common in southern Indiana.

I have found a few scattered groups of spring trigs in southernmost Fulton and Jasper Counties in Indiana. A thorough search failed to turn them up in neighboring Pulaski and Newton Counties. I may check again in a few years, on the possibility that the species is expanding northward.

One positive result was finding sulfur-winged grasshoppers in the East Main Street Prairie of Cary, Illinois. This adds McHenry to the counties where I have found the species. They probably occur in every county in my region but are common only on sandy or gravelly soils such as Cary’s kame-like hills. I have learned of another candidate site which may add Fulton County, Indiana, next year.

Sulfur-winged grasshoppers are characterized by bright yellow hind wings, which they rattle in flight to produce their song.

Prairie cicadas started a little late this year. I was pleased to find that management efforts to remove brush from the West Chicago Prairie Forest Preserve near my home appears to have paid off in both rebound of diverse prairie vegetation and an increase in the cicada numbers.

Prairie cicadas, are tiny, around an inch long.

Failure to perform such restoration work has a cost. Once known to occur in Kankakee County, prairie cicadas apparently are gone from there, the prairies having been degraded by brush, teasel and other invasive plants.

A final story is that of the periodical cicadas. In each cycle since 1973, the main appearance of 17-year cicadas in Chicago’s western suburbs has been preceded by a significant, 4-year-early emergence. This happened in 1969, 1986, and 2003. I suspect that in a small part of this area, all the cicadas now have switched to the early time. If you have done the math, you realize that it may happen again next year. One predictor to watch for are what I call oops cicadas, a few individuals who jump the gun by a year, or miss the main emergence and come out a year late. As expected, this has been happening this spring. I have heard 3 individuals myself in two cities and seen photos of the insects from 3 more. Counting and mapping them will be a highlight of next year’s early field season.

I predict that some areas will have good numbers of 17-year cicadas next year.

Southern Lessons

by Carl Strang

This year’s chapter in the series of annual bioblitzes organized by the Indiana Academy of Sciences took place at Eagle Creek Park in northern Indianapolis on June 2-3. This is early enough in the season that there were few singing insects for me to find, but I was able to gain valuable experience with two southern species that occur or have occurred in the Chicago region.

The first of these is the spring trig.

Female spring trig at Eagle Creek.

This species of tiny cricket first was described in 2014. That is surprising, given its abundance in southern Indiana and its extensive range beyond the state. It proved to be common in a range of habitats at Eagle Creek Park, from woodland edges to grassy meadows.

Spring trigs appear plain-faced to the eye, but bright light and magnification reveal a pattern of fine dark lines.

I learned more about the spring trig’s habitat, and found that I can hear them easily while driving at speeds of 30mph or less. This allowed me to get clarity on the species in the Chicago region. Driving in the southernmost counties, I found widely scattered small colonies in Fulton and Jasper counties, at road edges where wider bands of herbaceous plants were backed by woodlands. In the future I expect to find them in southern Pulaski and Newton counties, too, but not north of there.

Eagle Creek Park also has a large population of northern wood crickets.

The northern wood cricket is a forest species that is smaller and blacker than the spring field cricket, which could be heard chirping in the park’s meadow areas.

The spring field cricket is a few millimeters longer, typically has bronzy wings, and has a proportionately broader head and thorax.

Recordings I made during the bioblitz, and at home with a captive male, have provided further clarity on northern wood cricket song characteristics. Their chirps may never have 4 pulses (commonly 2 or 3), and almost never rise above 5 kHz in pitch, where spring field crickets often have 4-pulse chirps, and seldom drop below 5 kHz. Habitat also helps separate the two. I dug deeper into the literature, and learned more about historical records of the species in two Chicago region counties. Those observations were made in 1902, and I went to the sites in the weeks after the bioblitz. Northern wood crickets no longer occur there. I believe the records are correct, but that the crickets have gone extinct in those places. Northern wood crickets are reported to be sensitive to forest fragmentation, perhaps especially so in the northern fringe of their range, and such fragmentation clearly took place where they once were found in Lake and Marshall counties. I will continue to check the region’s larger surviving forest blocks, but it seems likely that the species no longer occurs in northern Indiana.

Incidentally, the other expected early-season singing insect, the green-striped grasshopper, lives in Eagle Creek Park’s meadows and prairie areas.

Next year’s bioblitz is expected to take place in one of my counties, and I am looking forward to the experience.

 

Wood Be? Wouldn’t Be!

by Carl Strang

For a couple years now, I have been pursuing early-season crickets that I thought must be northern wood crickets (Gryllus vernalis). These close relatives of our familiar spring field crickets (Gryllus pennsylvanicus) had been reported to occur in two of the counties in the Chicago region, both in northern Indiana. Spring field crickets are abundant in well-drained open grassy areas in my home county of DuPage, in Illinois. When I started hearing chirping Gryllus songs in Indiana woodlands and savannas, coming from accumulations of oak leaves often under trees, I figured these must be wood crickets.

For example, my attention was drawn to clumps of oak leaves surrounded by sand, along the Marquette Trail in the Indiana Dunes National Lakeshore. Nothing grassy about this!

A few days ago, I headed to the Marquette Trail to make another attempt to see one of these crickets. I wanted to confirm my suspicion, but also to get photos of a living northern wood cricket.

All I had were photos of museum specimens like this. Note the taper from the back of the thorax through the head. Spring field crickets are broader in front.

As I walked along a section of trail beside a road, I heard one of the crickets singing in a narrow band of accumulated oak leaves at the base of a hill.

An earlier controlled burn had removed nearly all the available cover. Puccoons bloomed magnificently above the line of leaves.

I made a sound recording of the singing cricket, and used the shotgun microphone to get his exact location. Then I lifted the layers of leaves to see if I could spot him.

You may be able to see the tunnels in the sand. At first I figured he made a quick retreat into them when I lifted the leaves.

If you look in the lower right-hand corner of the photo, however, you may see a small oval of reflected light. After taking the picture I discovered it was the cricket! I got him into a plastic cup.

I got my photos, and did my best to make him a northern wood cricket, but in fact he was a spring field cricket. Not only were his proportions wrong, but he held still and let me hold calipers just above him for a measurement. Spring field crickets usually are 16mm long, northern wood crickets 14mm, and this one was 16.8mm.

After reviewing my recordings, I think all the woodland Gryllus crickets I have heard in the region in fact are spring field crickets. There were small technical differences in song parameters between crickets in tree leaves and those in grassy areas, but I have to conclude that they don’t represent a species difference. The lesson ultimately is one of habitat. Spring field crickets on clay soils occur only in well-drained grasses. In sandy areas they broaden their habitat into woodland edges, and don’t associate strictly with grasses.

Further review of reference recordings points me toward northern wood crickets having more rapid chirping speed, and a lower pitch, resulting in a slightly less musical impression. So it’s back to square one for northern wood crickets in the region, and my insistence on visual confirmation of suspected but ambiguous species observations is vindicated.

Making a Case 3: Northern Wood Cricket

by Carl Strang

Last year I concluded that I had found northern wood crickets (Gryllus vernalis) in the Winamac State Fish & Wildlife Area in Pulaski County on June 13, based on habitat and sound recordings. In 2016 I returned to that site on May 29, but did not find them singing. On June 3 I heard Gryllus crickets chirping along the Marquette Trail, near the east border of Lake County, Indiana. All were in forest or savanna areas, the singers in deeply layered black oak leaves, usually in shade under black oak trees but some in isolated collections of leaves surrounded by sand.

One of the woodland crickets’ song sites near the Marquette Trail.

One of the woodland crickets’ song sites near the Marquette Trail.

None were in the open grassy areas favored by spring field crickets (G. veletis), even though such habitat was close by. I recorded two of these individuals, and later in the season recorded field crickets in meadow and prairie habitats favored by veletis but where vernalis would not be expected, plus another individual that by habitat should be vernalis, at the Kankakee Sands site in Kankakee County, Illinois.

The results seemed contrary to what would be expected from previous studies.

The likely vernalis (forest) had lower chirp rates than likely veletis (grassland).

The likely vernalis (forest) had lower chirp rates than likely veletis (grassland).

The number of pulses per chirp was unhelpful, with likely veletis ranging 2-4, likely vernalis 3-4. Linear regressions of the two sets of data show, perhaps significantly, the same slopes of chirp rate increase with temperature (physiology of closely related species expected to show a similar response to temperature). The linear regressions indicate that, for a given temperature, forest cricket chirp rates are 1.44/second less than grassland chirp rates. All data I can find in the literature for vernalis were collected from that part of their range where they are sympatric with the southern wood cricket (G. fultoni). Jang and Gerhardt (2005. J. Evol. Biol. 19:459–472) found that fultoni song characteristics differed between populations sympatric with vernalis and those allopatric to that species. They did not study allopatric vernalis. As my recordings may be the only ones that have been made where vernalis is allopatric to fultoni, and given the clear difference between recordings in habitats for likely vernalis and likely veletis described above, so far it appears that habitat, chirp rates and temperatures will be enough to establish the presence of vernalis. The major obstacle to finalizing this conclusion is confirming the identity of the forest crickets. So far I have been unsuccessful in efforts to catch or even see one. Next year I need to continue making recordings and trying to catch and measure suspected northern wood crickets.

Recent Travels: Places

by Carl Strang

I have fallen behind on blog posts. The season is heating up, and I have kept busy doing various surveys in various places. Today’s start on catching up will focus on some scenes and miscellaneous photos taken along the way.

The Marquette Trail at Indiana Dunes National Lakeshore passes beautiful marsh and sand savanna habitats.

The Marquette Trail at Indiana Dunes National Lakeshore passes beautiful marsh and sand savanna habitats.

I found northern wood crickets singing along the trail. They bury themselves in leaf litter like this.

I found northern wood crickets singing along the trail. They bury themselves in leaf litter like this.

Another example of a wood cricket song site. I tried to get a look at one, but they choose deeply stacked litter areas with plenty of hidey holes and escape routes.

Another example of a wood cricket song site. I tried to get a look at one, but they choose deeply stacked litter areas with plenty of hidey holes and escape routes.

Painted turtles wandered the savanna seeking good places to lay their eggs.

Painted turtles wandered the savanna seeking good places to lay their eggs.

Another good sand area is Illinois Beach State Park. Here a trail goes through the zone behind the fore dunes.

Another good sand area is Illinois Beach State Park. Here a trail goes through the zone behind the fore dunes.

Farther back from the edge of Lake Michigan, black oak savanna lines the trail.

Farther back from the edge of Lake Michigan, black oak savanna lines the trail.

Though my main interest was singing insects, there were many four-spotted skimmers to enjoy at IBSP.

Though my main interest was singing insects, there were many four-spotted skimmers to enjoy at IBSP.

I also have spent some time in Kendall County. This plains clubtail was at Hoover Forest Preserve.

I also have spent some time in Kendall County. This plains clubtail was at Hoover Forest Preserve.

This year’s Indiana Academy of Sciences bioblitz was at Goose Pond in southern Indiana. I stopped on the way down for a walk at Turkey Run State Park. Ravines there provide many scenes like this.

This year’s Indiana Academy of Sciences bioblitz was at Goose Pond in southern Indiana. I stopped on the way down for a walk at Turkey Run State Park. Ravines there provide many scenes like this.

I didn’t end up taking any scenery shots at Goose Pond. As I was setting up the UV light, I found this mama spider crossing the road, her back covered with babies. All their eyes glittered like jewels in the headlamp.

I didn’t end up taking any scenery shots at Goose Pond. As I was setting up the UV light, I found this mama spider crossing the road, her back covered with babies. All their eyes glittered like jewels in the headlamp.

Northern Wood Crickets

by Carl Strang

Those of you on the mailing list for my annually updated guide to the singing insects of the Chicago region would look in vain for northern wood crickets in last year’s edition. I simply wasn’t aware that they could be here. While preparing for the Hills of Gold bioblitz, however, I found that their range extends into our region. I had not included them in the hypothetical list because initially it was directed toward DuPage County in Illinois, and wood crickets never have been found in northeastern Illinois. I gained some experience with wood crickets in the bioblitz, and the sound recordings I made there proved to be of the northern wood cricket, Gryllus vernalis. Study of the relevant scientific paper (Yikweon Jang and H. Carl Gerhardt. 2006. Divergence in the callling songs between sympatric and allopatric populations of the southern wood cricket Gryllus fultoni [Orthoptera: Gryllidae]. J. Evol. Biol. 19: 459–472) indicated that the 2-chirp-per-second, 3-pulse-per-chirp, songs coming from leaf litter in forest habitat, were of northern wood crickets. Southern wood crickets, the other possibility, would have had faster chirps at that temperature.

Last week’s vacation survey trips went so well, despite two days lost to rain, that I had Saturday available to seek northern wood crickets the Indiana portion of the Chicago region (I had not found them in the Illinois, Wisconsin or Michigan excursions). My first two stops, in St. Joseph County’s Bendix Woods and Fulton County’s Judy Burton Nature Preserve, were fruitless. Mid-afternoon brought me to the Winamac State Fish and Wildlife Area in Pulaski County, and I drove the gravel roads until I found one of the parking lots in a forested spot. Immediately I heard the chirps of Gryllus crickets, and I dug out the Marantz sound recorder. As I recorded two different crickets I believed I was hearing 3 pulses in the chirps, as had been the case at the bioblitz.

This was where the cricket in the recording shared below was located.

This was where the cricket in the recording shared below was located.

I would have liked to try and flush out one of the singers, but as the photoflash lighting in the photo suggests, it was getting dark fast, and I barely reached the car before the downpour hit. I tried to get around the storm by driving to the Jasper-Pulaski Fish and Wildlife area, but no dice, and I had to call it a day. So, here is a cut of the stronger recording:

Can you distinguish the 3 pulses that form each chirp?

The visual rendition of the recording clearly shows the 3-pulse chirps, but they are being produced at a 4-chirp-per-second rate.

The visual rendition of the recording clearly shows the 3-pulse chirps, but they are being produced at a 4-chirp-per-second rate.

This might have been confusing, given that the southern wood cricket, not yet known from northern Indiana, more typically has a 4-chirp rate, but the soil temperature was very warm, at nearly 80F, and the scatter for vernalis in Jang and Gerhardt’s graph extends to 4 chirps at that temperature. Also, the dominant frequency was 5.9kHz, good for vernalis but pitched way too high for fultoni at any temperature. So, I am content for now that I have established a present-day northern wood cricket presence in the region. One goal for next year will be to seek them in more locations, make more recordings, and get a better sense of their song features in this part of their range.

Hills of Gold

by Carl Strang

This year’s chapter in the bioblitz series organized by the Indiana Academy of Science was called Hills of Gold. It was on a beautiful site being assembled by the Central Indiana Land Trust, and when complete will occupy around 2 square miles in Johnson County, south of Indianapolis.

The event took place on an intermittently rainy day, as illustrated by this less than sharp image of a representative bit of forest and one of the old logging trails we used to get around the site.

The event took place on an intermittently rainy day, as illustrated by this less than sharp image of a representative bit of forest and one of the old logging trails we used to get around the site.

Usually my role in these bioblitzes is to survey singing insects, but this was too early in the season for a sufficient number of species to justify my participating. I decided to reconnect with my experience studying forest Lepidoptera ecology in the 1980’s, and took on moths as well. As I walked the forest during the day, I found many beautiful plants and animals outside my target groups that gave joy.

Green dragons always make me smile, and I ran across a magnificent cluster of them along one of the streams.

Green dragons always make me smile, and I ran across a magnificent cluster of them along one of the streams.

And who can say “no” to fire pinks? Hummingbirds sure don’t.

And who can say “no” to fire pinks? Hummingbirds sure don’t.

Violet wood sorrel is a plant I haven’t encountered very often.

Violet wood sorrel is a plant I haven’t encountered very often.

There also were insects to note outside my target groups.

This Bombus impatiens queen still had not found a nest site, and was prospecting the forest floor.

This Bombus impatiens queen still had not found a nest site, and was prospecting the forest floor.

I interrupted this female scorpionfly’s feed on an emptied caterpillar skin.

I interrupted this female scorpionfly’s feed on an emptied caterpillar skin.

Speaking of caterpillars, the first target species I found was this eastern tent caterpillar:

They already had reached the final instar and were starting to pupate.

They already had reached the final instar and were starting to pupate.

I collected only four moth species during the day. All were fairly common.

This was one of them, which I identify as the unadorned carpet, a member of the inchworm family.

This was one of them, which I identify as the unadorned carpet, a member of the inchworm family.

Many more moths came to my ultraviolet light setup that night. Stay tuned for that episode.

For the record, there was one singing insect. This was my first encounter with a wood cricket. I heard them scattered thinly all through the forest, but never succeeded in seeing one. They probably were northern wood crickets (Gryllus vernalis), but might have been southern wood crickets (G. fultoni). I made a couple good sound recordings, which I hope will allow me to make the determination.

One of them was singing from this patch of leaf litter.

One of them was singing from this patch of leaf litter.

More on that later, after I have analyzed the recordings.

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