Sound Ideas: Japanese Burrowing Cricket

by Carl Strang

One of the unexpected findings from the field season just past was the discovery of Japanese burrowing crickets at Bendix Woods in St. Joseph County, Indiana.

Japanese burrowing cricket

Japanese burrowing cricket

As described earlier, there is a well-established population of this exotic species in the gravel-filled medians dividing parking lots and drives in the central part of the park. They are well buried, and it was only their distinctive songs that gave them away.

The chirps are distinctly buzzier than those of the fall field crickets that were singing nearby. Here is a fall field cricket recording from 2006 for comparison.

Listening to it, I’m getting a warm reminder of summer. Common true katydids, a striped ground cricket, and wall-of-sound tree crickets and other ground crickets are in the background.

 

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Sound Ideas: Common Ground Crickets

by Carl Strang

There are 3 species of ground crickets that occur throughout the Chicago region (I still lack 2 county records for one of these, but expect to make up that deficit on a future Wisconsin trip). The ground crickets are the LBJ’s of singing insects (birding jargon: “little brown jobs” refers to sparrows, wrens and the like which are quick to vanish before they can be identified). Most ground crickets look identical at first glance, are tiny, and usually are brown. I’ll begin with the striped ground cricket.

The stripes are clear on this female striped ground cricket’s head.

The stripes are clear on this female striped ground cricket’s head.

This is the weediest of the ground crickets, first to show up in disturbed sites, and abundant in lawns. Its song consists of separate brief rough buzzes, continuously produced at 2 to 3 per second. It is low enough in pitch to hear easily, with most of the buzz’s sound range below 7 kHz. Here is a recording (complete with background bird songs and the usual traffic rumble):

The second species also occurs in open areas, but mainly where the grass is taller and vegetation better established.

Allard’s ground cricket is a close relative of the striped. The head stripes are absent, faint, or incomplete, however.

Allard’s ground cricket is a close relative of the striped. The head stripes are absent, faint, or incomplete, however.

The song consists of incessant, separate quick very high-pitched notes (6 kHz) that sound like 4-6 per second but sonographs show twice that rate. There are fairly frequent, very brief pauses (again, birds and this time a train in the background):

Now I will toss in a fourth species. The tinkling ground cricket is less widely distributed than the others (so far I have found it in half of the region’s counties), but include it here to provide a comparison to the Allard’s song. Here is a recording:

The song consists of high pitched (7 kHz) individual notes, like those of Allard’s ground cricket but distinctly slower at a given temperature (1/3 to ½ as rapidly produced). It often is rendered “tink-tink-tink…” The song is uninterrupted, lacking the frequent breaks characteristic of Allard’s ground cricket (this is especially helpful late in the season, when Allard’s often slows down). The tinkling ground cricket lives in open woodlands and woods edges, and is especially abundant on sandy soils. It looks different, too.

Tinkling ground crickets have reddish tones that distinguish them from our other ground crickets.

Tinkling ground crickets have reddish tones that distinguish them from our other ground crickets.

The final, common species is the Carolina ground cricket.

The Carolina ground cricket has faint head stripes. The female is distinguished by an unusually short ovipositor.

The Carolina ground cricket has faint head stripes. The female is distinguished by an unusually short ovipositor.

Its song is a continuous, irregularly pulsed drone, purr or trill with periods when additional pitches are added to the song, making it more dissonant. Though the sound pulses are broad enough in pitch range to qualify as a drone, it is not far from a trill, and low enough in pitch to be heard by most, at 6 kHz. Here is a recording:

As the passing geese perhaps imply, Carolina ground crickets prefer moist habitats, from wetland edges to bottomland forests. In my residential neighborhood they are fairly common, but stick to the cooler, moister foundation shrub plantings against the houses.

We’ll have to wait a while to hear these crickets again. They winter in the egg form, and need until the very end of June or, more often, July to develop to the point where they begin singing.

The Transformed Block Count

by Carl Strang

The developers who built my subdivision, in their wisdom, decided to plant mostly green ashes along the streets. That brilliance has been answered in the form of an insect, the emerald ash borer. This little invasive ash-killer has done a number on my neighborhood. A series of before-and-after shots follows, going around the block route I follow when I do my standard survey of singing insects in the warm months.

Looking north along my street in 2009.

Looking north along my street in 2009.

The same block now.

The same block now.

Turning west in 2009.

Turning west in 2009.

Same view, 2013.

Same view, 2013.

The next block, looking south in 2009.

The next block, looking south in 2009.

And now.

And now.

The final leg, facing east in 2009.

The final leg, facing east in 2009.

Hard to believe it’s the same block today, but it is.

Hard to believe it’s the same block today, but it is.

Most of the tree loss happened over a brief period of time, the second half of summer last year. Ever the opportunist, I made predictions about the response of the three singing insect species common enough for statistical comparisons between this year and last. Greater angle-wings are tree-dwelling katydids, and so I expected their counts to drop. Carolina ground crickets mainly live beneath foundation shrub plantings, so I expected no significant change. Finally, striped ground crickets prefer sun-lit lawns to shade, so I expected their numbers to increase. I was correct on two of the three predictions.

The Carolina ground cricket median count in 2013 was 7, not significantly different from 2012’s median of 5 (Mann-Whitney U-test of the ranks of all the counts led to a z statistic of 2.05, p>0.01). The median count of striped ground crickets in 2013 was 20, that in 2012 was 11. The comparison of ranks produced a statistically significant z value of 3.89 (p<0.01). I was somewhat surprised at the lack of a demonstrable difference for greater angle-wings (z = 1.00, p>0.01). The 2013 median count was 3, less than the 2012 median of 5, but the difference was not as large as one might expect. There were enough surviving trees of other species to sustain a population of the katydids, and also the removal of the nearer trees made more distant angle-wings more audible.

The Other Side of Range Extensions

by Carl Strang

The aspect of singing insect studies that has been of greatest general interest, and about which I have presented talks most frequently, is range extensions. Most of the several examples uncovered so far have been northward extensions of species ranges, and it is easy to jump to the conclusion that this is a product of global climate change.

The first species I found well north of where it previously had been known was the broad-winged tree cricket.

The first species I found well north of where it previously had been known was the broad-winged tree cricket.

If climate is the primary influence in these range extensions, we would expect the southern boundary of a species’ range to shift north as well. However, sticking with the example of the broad-winged tree cricket, its range has expanded south as well as north. I know that only because Tom Walker, the authority responsible for the Singing Insects of North America website, informed me that he has found them spreading down into parts of Florida where they had not been before.

Documenting an expansion northward is easier than demonstrating a disappearance in the south portion of a species’ range. It is easier to prove a positive than a negative. Also, when one has limited time and financial resources, it is not possible to travel south and conduct the necessary regional surveys. So, what to do?

The best idea I have had so far is to identify species whose southern range boundaries occur in my region, and make a point of documenting their presence and estimating their abundance from year to year. There are four best candidates.

The dog day cicada Tibicen canicularis has the northernmost southern range boundary. It is mapped down into the very northern edges of Indiana and Illinois, but I have found it a little farther south, at Braidwood Dunes in Will County, Illinois, and in southern Marshall County, Indiana. My notes suggest that its numbers may vary considerably from year to year in the latter location.

Dog day cicada

Dog day cicada

The broad-winged bush katydid Scudderia pistillata is mapped a little farther south, but I have found it infrequent in DuPage County, Illinois, and its season of activity seems to conclude sooner here than it does farther north. So far my surveys have turned it up in Lake County, Illinois, as well, but not farther south.

Broad-winged bush katydid

Broad-winged bush katydid

The striped ground cricket and sword-bearing conehead are abundant in the region. Their southern range boundaries are mapped about half a state south, but that is the same distance as a number of the northern range shifts I have observed. If entire ranges are shifting, one would expect them to be more scarce.

Sword-bearing conehead

Sword-bearing conehead

This is yet another topic of interest I am keeping in mind while surveying the region’s singing insect species.

Dispersal Ability

by Carl Strang

In order for us to understand insects well enough to know which ones need the most attention in conservation, there are some pieces of information we need: how abundant they are, how broad or narrow their habitat needs, their reproductive potential, and their dispersal ability. The first two items are readily obtained in the course of a regional survey such as I am conducting for singing insects in northeast Illinois and counties in neighboring states. Reproductive potential has been studied to some extent and can be found in the literature for some species. Dispersal ability is a critical point that is not well studied as far as I can tell, and so it is good to take advantage of observations that reveal which species spread easily, and which ones do not.

Over the past two weeks I spent much time in the St. Joseph Hospital in Mishawaka, Indiana, where the medical professionals saved my mother’s life.

The hospital was built 3-4 years ago, and is surrounded by extensive areas planted mainly in native prairie plants.

The hospital was built 3-4 years ago, and is surrounded by extensive areas planted mainly in native prairie plants.

Occasionally I took walks along the paths, or made observations while arriving or departing. The species present in the plantings can be regarded as ones with high dispersal ability. These included field crickets (I cannot be sure which, as this was the cusp between the spring and fall field cricket seasons), striped and Allard’s ground crickets, Carolina grasshoppers, Roesel’s katydids, and a sword-bearing conehead. All of these are regionally abundant, and fairly broad in their habitat (dry to mesic mixes of grasses and forbs). Three have good flying ability (in the case of Roesel’s, there are long-winged individuals as well as medium and short-winged ones). Field crickets and the ground crickets can take advantage of their regional abundance and tendency to hop and walk over land. One limitation here is that I was only able to make observations over a brief portion of the season.

If I had to point to the weediest singing insect in our region, I’d have to say it’s the striped ground cricket, which is the quickest to appear in a new site.

First and Last Song Dates

by Carl Strang

I now have 7 years’ data in which I have noted the first and last dates on which I heard each singing insect species. This year was characterized by a mild winter followed by a warm spring and then a summer of drought. The mild winter and spring apparently were responsible for this year’s early phenology. First song dates were the earliest I have recorded in DuPage County for 17 of the 21 species for which I have 7 years of records. The chi-squared value of 77.33 (with an expected value of 3 species per cell for each rank of earliest to latest) is, of course, statistically significant.

The greater angle-wing started earlier and finished earlier this year than in any of the previous 6 years.

The greater angle-wing started earlier and finished earlier this year than in any of the previous 6 years.

As for last song dates, singing insects generally finished early this year. Of the 20 species for which I have 7 years’ data, 15 had their earliest or second-earliest ending dates, and the chi-squared value was a statistically significant 22.68. This was not a particularly cold or dry late summer and autumn, so the implication is that singing insects have a fixed rate of attrition or duration of song season, so that an early start results in an early finish. The 12 species for which I have the best, most reliable records do have differences in observed song season lengths (ranges for the 7 years, and ranked lowest to highest: 18-42 days for Roesel’s katydid, 16-52 days for gladiator meadow katydid, 52-96 days for the greater angle-wing, 58-96 days for snowy tree cricket, 67-91 days for the scissor-grinder cicada, 64-94 days for the greenstriped grasshopper, 62-109 days for Linne’s cicada, 72-105 days for the dog day cicada, 81-107 days for the common true katydid, 107-139 days for Allard’s ground cricket, 111-141 days for striped ground cricket, and 113-143 days for Carolina ground cricket).

The number of clear, cold nights seemed high enough in November that they might partly explain the early conclusion of common ground cricket songs this year, especially given the recent study by MacMillan et al. (2012) indicating that there is a metabolic cost to recovering from cold-temperature paralysis. However, I found no significant relationship between last song dates and the number of November days with low temperatures below 33F over 2006-2012 for any of the three species (Spearman’s r values 0.51 for Allard’s ground cricket, -0.39 for striped ground cricket, and 0.33 for Carolina ground cricket). It is interesting, though, that I have seen a few red-legged grasshoppers active a couple weeks after the last ground cricket.

An early December red-legged grasshopper

An early December red-legged grasshopper

This bigger insect may have larger fat reserves to draw upon and so extend its season.

Common Ground Crickets

by Carl Strang

Ground crickets are the most difficult group of singing insects to photograph. I have spent hours seeking the various species, and still do not have photos of both genders of several species for the guide I have been developing for the Chicago area. Females are easier to find. For one thing, they wander more.

Females come out into the open sometimes as they travel in search of singing males or oviposition sites.

The acrobatic individual in the above photo is a Carolina ground cricket. I also held one in a jar briefly, but when I released her she escaped before I could get a sharp photo.

Of our common three ground cricket species, the Carolina female is distinguished by her short ovipositor, shorter than the femur length.

Of course, to some degree if you have seen one ground cricket you have seen them all. Here is a female striped ground cricket.

The longer ovipositor, subtle differences in body proportions, and especially the stripes on the head separate this one from the Carolina ground cricket.

The third common species is Allard’s ground cricket. Here is an earlier photo of a female.

There is head striping here as well, but sometimes it is obscure.

Fortunately for monitoring purposes, the male songs of these three species are easily distinguished. And after all, since they are going mainly by the songs themselves, there is little if any selective pressure for them to look different. Still, I want those photos. I still need one of a male Carolina, and that is my final field research goal for this season.

Learning to Identify Insect Songs

by Carl Strang

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

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

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

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

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

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

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

Linne’s cicada

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

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

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

Block Count Summary

by Carl Strang

Neighborhood block counts are a survey method I have developed in my singing insects study. They consist of walks around the block in my residential neighborhood in Warrenville. I record the time and temperature, and count only the insects whose individual songs I can distinguish from the general background of tree cricket and ground cricket songs. I try to include a mix of times, especially early in the season to include cicadas, but concentrate most of the effort after dark when most species are singing. The overall species count in 2011 was 14 (no new species this year).

One of the streets on the block.

Most of these insects do not occur in high enough numbers to permit statistical comparisons between years. The high counts for each species this year were as follows: 1 for fall field cricket, jumping bush cricket, Say’s trig, and Davis’s tree cricket; 2 for Allard’s ground cricket and dog day cicada; 3 for snowy tree cricket, 4 for narrow-winged tree cricket, 5 for common true katydid, 8 for two-spotted tree cricket, 10 for Linne’s cicada, 14 for Carolina ground cricket, 16 for greater anglewing, and 26 for striped ground cricket. Most of these are typical of the past five years. Apart from statistical comparisons to follow, there seems to have been a decline in fall field crickets over that period (high counts of 5 in 2007, 4 in 2006, and 1 in the recent years, but in 2011 that count was on only one occasion).

Only three species occur consistently in large enough numbers to justify statistical comparisons between years. There never have been statistically significant differences between adjacent years in striped ground cricket counts, and the same was true in this year’s comparison with 2010 (overall medians 14.5 in both years; Mann-Whitney U-test, z = -0.14, P>0.01). Carolina ground crickets likewise were not different (median 4 in 2010, 7 in 2011; z = -2.07, P>0.01). Greater anglewing counts did show a statistically significant increase over last year (median 1 in 2010, 4 in 2011; z = -3.30, P < 0.01), and in general they and the fall field crickets have been the most volatile.

A Small Mystery Solved

by Carl Strang

From time to time I have puzzled over a cricket’s trill I have heard in scattered places on the mansion lawn at Mayslake Forest Preserve. I have called them Say’s trigs, because that was closest to the sound of the trill, but two things bothered me: I haven’t found these trigs in mowed lawns elsewhere, and the quality of the sound wasn’t exactly right. Say’s trigs usually are found in dense herbaceous vegetation, or sometimes are up in the foliage of shrubs.

Earlier this week I decided to record that trill for comparison to references. While the mini-disk was recording, it occurred to me that I might take advantage of my shotgun mike’s directionality to try and find the singer. Listening through the headphones eliminated any ventriloquial confusion, and I was able to locate the source within 2 inches. I didn’t see a cricket, but there were two nightcrawler tunnels there.

Further study of the ground revealed that there also are a lot of significant cracks in the soil.

The unimpeded sound I got from close up confirmed that these are indeed Say’s trigs. Something about this lawn, or this population of crickets, has them behaving differently from conspecifics elsewhere. It occurs to me that one possibly significant difference is that there are very few striped ground crickets in the Mayslake lawn, while in practically every other DuPage County lawn they are common. Something about this place apparently causes trigs to replace striped ground crickets. I titled this post “A Small Mystery Solved,” but as so often is the case I have replaced one mystery with another.

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