Morgan Monroe-Yellowwood Ecoblitz

by Carl Strang

The Indiana Forest Alliance is sponsoring a multi-year species survey of the back country portion of the conjoined Morgan Monroe and Yellowwood State Forests in Monroe and Brown Counties of southern Indiana. They are holding bioblitz weekends at various seasons so as to get a more complete picture than a single bioblitz would produce. Jeff and Mary Stant are providing the principal organizational and logistical support. I paid my first visit on September 12 to begin inventorying the singing insect species.

While waiting my turn to go into the survey area, I checked out the base camp in an old field with scattered young trees adjacent to the riparian edge of a wooded stream. The species mix was much like I would expect to find in a dry area in northern Indiana or Illinois.

Woodland meadow katydids were very common in woodland edges, much more abundant than I have found them farther north.

Woodland meadow katydids were very common in woodland edges, much more abundant than I have found them farther north.

The old field held scattered common meadow katydids.

The old field held scattered common meadow katydids.

Handsome trigs also were common in the riparian edge.

Handsome trigs also were common in the riparian edge.

Allard’s ground crickets were one of several species at the camp.

Allard’s ground crickets were one of several species at the camp.

The forested survey area was, as expected, less diverse, though the cool afternoon temperature probably inhibited some species. The slopes held scattered confused ground crickets, and bottomland herbaceous thickets were full of Say’s trigs, along with good numbers of Carolina ground crickets and more scattered jumping bush crickets and narrow-winged tree crickets.

At one point we flushed out a medium-sized cricket which permitted a quick photo but evaded capture. It was one of the camel crickets, probably in genus Ceuthophilus.

At one point we flushed out a medium-sized cricket which permitted a quick photo but evaded capture. It was one of the camel crickets, probably in genus Ceuthophilus.

We went up to a ridge top in the evening. It was very cold, and few species were managing to sing. There were scattered tinkling ground crickets, Carolina ground crickets, jumping bush crickets, and a few feebly ticking long-spurred meadow katydids. A background hum came from the forest canopy, and occasional individuals could be distinguished to support an identification of Davis’s tree crickets, by far the most abundant singers on that cold night.

I look forward to returning for more ecoblitz weekends next year.



Museum Encounter

by Carl Strang

One of my responsibilities is to curate the Forest Preserve District of DuPage County’s natural history collection. Recently I was cataloguing some drawers of insect specimens when I noticed two tree crickets that had been collected in Wheaton a couple of decades ago, but had not been identified. These proved to be a pair of Davis’s tree crickets, a species I have heard singing in several locations but never have seen, as they generally remain high up in the tree canopies.

In dorsal views these appear to be rather generic, as tree crickets go.

In dorsal views these appear to be rather generic, as tree crickets go.

However, under the magnifying glass the basal antenna segments prove them to be Davis’s. Each segment shows a single straight black line. It would be curved or hooked in the narrow-winged tree cricket, or there would be an additional spot if this were one of the meadow-dwelling species.

However, under the magnifying glass the basal antenna segments prove them to be Davis’s. Each segment shows a single straight black line. It would be curved or hooked in the narrow-winged tree cricket, or there would be an additional spot if this were one of the meadow-dwelling species.

This was a reminder of the value of museum collections. Though I seldom collect specimens in my singing insects survey, that is because it seldom is necessary. For the most part, insect songs are distinctive, and if anything are more so than their physical characteristics. Because the insects distinguish themselves by sound, selective pressure on visual features is relatively weak. Sibling species pairs and groups can be found in most major singing insect categories. For example, the Tibicen cicadas closely resemble one another, as do the coneheaded katydids, the ground crickets, the field crickets, many of the meadow katydids, the bush katydids and, as in the present example, many of the tree crickets.

That said, I take voucher specimens in the rare circumstances when songs don’t tell enough of the story, and preserve specimens that I inadvertently damage when handling them to confirm identifications.

False Alarm

by Carl Strang

A recent moment of excitement proved to be unfounded. I was hosing off the driveway, preparatory to sealing it, when the spray flushed out a tree cricket hidden in the siding.

The color spot seemed confined to the head. Could this be a Davis’s tree cricket?

The color spot seemed confined to the head. Could this be a Davis’s tree cricket?

I never had seen a Davis’s, though I have heard them singing several times. They generally stay high up in trees, and their songs are so buried in the nighttime wall of sound produced by other singing insects that I don’t have a good sense of their abundance or distribution. I spent a good half hour photographing this female before it occurred to me to check the basal antenna spots.

The curved, hook-like shape of the spot on the basal segment told me this was not a Davis’s, whose spot simply would be straight, but rather a narrow-winged tree cricket, a very common species.

The curved, hook-like shape of the spot on the basal segment told me this was not a Davis’s, whose spot simply would be straight, but rather a narrow-winged tree cricket, a very common species.

Nevertheless, there are lessons to be learned in every experience, and now I have a usable photo of the narrow-wing’s spots.


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.

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.

Arboreal Tree Cricket Songs

by Carl Strang

This year I finally was able to resolve my confusion about the songs of three arboreal tree crickets. The first breakthrough came from observing singing male two-spotted tree crickets, as I mentioned in an earlier post.

Two-spotted tree cricket (male)

After further study I developed a description of the two-spotted tree cricket song that I feel confident about. Their songs are composed of variable-length trills, 1 second to 7 seconds or longer duration. Spaces between trills can be very short or longer, but when longer usually are filled by a stuttering sound. Often their song seems more discordant or strained than those of the others. Both two-spotted and narrow-winged tree cricket songs are distinctly higher pitched than the song of a common reference, the snowy tree cricket, but not necessarily well separated from one another. When there is a slight difference, the two-spotted has the slightly higher pitch.

Narrow-winged tree cricket

Trill length and the spaces between trills are very consistent in narrow-wings, forming a regular rhythm, unlike the variable two-spotteds. Spaces between always are distinct, longer than the brief pauses most characteristic of two-spotteds, and do not contain stutters. The trills are brief, a couple of seconds long. There was a difference in when the species started, with the first two-spotted singing at the beginning of August, narrow-wings not beginning until the end of the month. Both species continued to the end of September.

On two occasions I heard what could only be a Davis’s tree cricket. The long continuous trill, lower pitched than that of the snowy’s song, occasionally was broken. The cricket was well up in an ash tree. Though I only heard this one, I now suspect that I seldom hear them because their usual location is high in trees, according to the literature, where the higher-pitched chorus of other nocturnal crickets may obscure their songs. The lower pitch and much longer trill matches written descriptions in the literature, if not reference recordings (which give the impression that trills are more interrupted than in fact they are). For reference recordings, go to the Singing Insects of North America website or the Songs of Insects website.

Block Count Results

by Carl Strang

Earlier in the season I described my block counts of singing insects, in which I walk around the block where I live, counting the singing insects I hear. In these counts I heard 13 species in 2009, compared to 15 in 2008. The two missing species were the dog day and scissor-grinder cicadas, both of which I heard on my block at times other than sampling sessions.

Only 3 species have been present in large enough numbers to allow comparisons between years. Most abundant is the striped ground cricket, with median counts of 13, 14.5, and 12 for 2007, 2008 and 2009, respectively*. Statistical tests found no differences among years in the striped ground cricket.

Median counts of Carolina ground crickets were 3, 3, and 7 for the three years. The change from 2008 to 2009 was statistically significant. The third species, the greater angle-winged katydid, produced median counts of 7, 1, and 0. The drop between 2007 and 2008 was statistically significant, but that from 2008 to 2009 was not.

The other species I have noted in my neighborhood, in rough descending order of abundance, are two-spotted tree cricket, snowy tree cricket, fall field cricket, narrow-winged tree cricket, Linne’s cicada, common true katydid, Allard’s ground cricket, and a few species I have heard very infrequently: jumping bush cricket, Say’s trig, Davis’s tree cricket and possibly fork-tailed bush katydid.

*For those interested in the technical details, I included only counts in August-October, the months when these species appeared consistently. Total numbers of counts were 49, 46 and 35 in the three years, respectively. I am very conservative in my use of statistical tests. Here I used the large-sample version of the Mann-Whitney U-test, a nonparametric test which produces (ironically?) a z test statistic. Non-parametric tests are needed for count data, and I seldom see anything like a normal distribution in the aspects of nature I study, anyway. Test statistic values for striped ground cricket counts were z = -0.73 for 2007 vs. 2008, and -1.58 for 2008 vs. 2009, both P > 0.01. Again, being conservative, I use the 1% rather than the 5% level of error. Carolina ground cricket counts showed no change between 2007 and 2008 (z = -0.68, P > 0.01), and an increase from 2008 to 2009 (z = -3.32, P < 0.01). Greater angle-wing counts showed a decrease from 2007 to 2008 (z = -3.33, P < 0.01), but no change from 2008 to 2009 (z = 0.32, P > 0.01).

Gadget 1

by Carl Strang

For the most part in this blog I am trying to model methods of inquiry that don’t rely on technology. Our human senses have their limitations, but we can gather enough information through them to answer a lot of questions about our surrounding wild world. Nevertheless, there are occasions when gadgets can help. Today I will feature one of those I have found useful in my field studies of singing insects: my soprano recorder.

Recorder b

I don’t have perfect pitch, but I have a reasonably good ear. I have found the recorder to be especially helpful as I tackle the problem of the arboreal tree crickets (outlined in my earlier post on one of them, the two-spotted tree cricket ). This season one of my goals has been to sort out the songs of the two-spotted, narrow-winged and Davis’s tree crickets. I was encouraged when I noticed that Elliott and Hershberger, in their recent book on singing insects, indicated that these three species should have distinct pitches in their songs. Highest should be the two-spotted, at 3.5 kHz (kilohertz, a quantitative sound frequency measurement), which translates to a pitch of A, the fourth A above middle C. In the middle should be the narrow-winged tree cricket, at 3 kHz or approximately F-sharp, the fourth F-sharp above middle C, 3 half-tones below the two-spotted. I noticed, incidentally, that the distinctive song* of the snowy tree cricket also is indicated to be at 3 kHz, and so I had hopes that this would provide a rough and ready field standard. The lowest of the arboreal tree crickets, according to Elliott and Hershberger, is the Davis’s tree cricket, at 2.5 kHz. This translates musically to the fourth E above middle C, distinctly lower than any of the others. So, recorder in hand, I set forth.

Snowy tree cricket 5b

Snowy Tree Cricket

Two caveats quickly became clear. First, the pitch of a given species is subject to change with environmental temperature, rising and falling as the temperature rises and falls. Second, I have to keep in mind that my own hearing may not well match the measuring devices used to provide the information in that book. In general all species sounded, to my ear, a good 3 tones lower than Elliott and Hershberger suggested.

I have found that to my ear, both two-spotted and narrow-winged tree crickets have songs distinctly higher pitched than that of the snowy tree cricket. At a given temperature, the two-spotted sings one-half to a full tone higher than does the narrow-winged. However, at a given general temperature, narrow-wings range over half a tone of pitch or more. Whether this is because the microclimate is different where individual crickets are singing, or whether this is something they are controlling, I cannot say. It means, though, that I have to rely as much or more on the temporal pattern of the song to distinguish these two species.

Narrow-winged Tree Cricket

Narrow-winged Tree Cricket

Narrow-wings sing with a steady pattern of trills and spaces, with trills of equal lengths and spaces of equal lengths, and the spaces are significant at a second or so duration. Two-spotteds sing at a little higher pitch on average, have trills of varying lengths including some often lasting well over 5 seconds, usually with at least some pauses that are very brief, as though catching a quick breath.

I recently heard, on my neighborhood block count, what I believe must have been a Davis’s tree cricket. The insect was high up in a tree. Its trills were variable but generally very long, with only occasional odd interruptions. Spaces were short. Significantly, the pitch was down at A-flat, low for the temperature, which was 70F. Based on my recorder tests, at that temperature I would expect snowy tree crickets to be singing at B or C, two-spotteds at the E above that, and narrow-wings at C to E. So, the recorder is a helpful tool, but in distinguishing the songs of these crickets I find that the pattern of their song is more reliable than the pitch.

*You know the song of the snowy tree cricket, even if you live outside its range. In the movies, whenever the director wants to convey a calm nighttime mood, there will be a snowy tree cricket in the sound track. The song is a pulsing tone, varying with the temperature so that if you count the notes in 15 seconds and add 40, you have the temperature in degrees Fahrenheit. Though the narrow-winged tree cricket’s song likewise is a regular pulse, the tones are on the order of 2 seconds’ duration with a 1-2-second space between. Unless the temperature is very cool, the snowy’s song is much faster.

Two-spotted Tree Cricket

by Carl Strang

One of the goals in my singing insects study this year is to sort out the songs of three arboreal tree crickets. In the field I have found that their songs are not as distinct from one another as reference recordings and descriptions seemed to suggest. Two of the three species I have seen, and so confirmed their presence in DuPage County. Today I begin with what I suspect may be the only one singing as early in the season as late July and early August: the two-spotted tree cricket.

Two-spotted tree cricket 1b

This photo shows a female, with the two large spots on her back that give the species its name (males lack them, and are pale). She sits on the arm of one of the 2006 Roger Raccoon Club  kids, who brought her to me for identification. Until two weeks ago, she was the only one I had seen. Certainly the references were correct in saying these are not easy to find. They live in trees, often well above the ground. The male’s song, which you can find here  or here, is a strained, often dissonant sounding trill that is interrupted fairly frequently by brief pauses that often are filled with stuttering sounds. Unfortunately, the same description applies more or less to the songs of Davis’s tree cricket and the narrow-winged tree cricket, though the tone of the last seems more melodic to my ear.

Two-spotteds begin to sing at dusk. On August 6 I was at Timber Ridge Forest Preserve, strolling the Great Western Trail with ears open for insect songs, when scattered tree crickets in this target group began to sing. All had identical songs, but one in particular seemed to be closer to the ground and just off the trail. After a short time I found him.

2-spotted singing b

He was on the underside of a big grape leaf. Here he is close up.

2-spotted singing cropped b

He was using a trick for which some of the tree crickets are known. He had chewed a circular hole in the leaf, and was using it to amplify and possibly direct his song (tree crickets sing by elevating their wings and vibrating them against one another).

2-spotted wings down b

I made a recording, then prepared to collect him for identification. But when I put my flashlight on him again I found this was unnecessary.

2-spotted pair 2b

A female had arrived on the scene, and there was no mistaking her identity. The male kept his wings elevated, and continued to vibrate them occasionally in song. She was palpating her way slowly up his back in search, I believe, of secretions that some of the tree cricket males provide as nuptial food gifts in a prelude to mating.

2-spotted pair 1b

The next evening at dusk I was at Springbrook Prairie Forest Preserve. I heard the same song coming from near the top of a 15-foot-tall bur oak beside the trail. Looking up toward the point from which the sound seemed to be coming, I noticed that one of the leaves had a circular hole in the middle. When I illuminated it with my flashlight, sure enough, there was another male two-spotted tree cricket. So, at least with plants having relatively large leaves, I now know to look for distinctive circular holes that may help me to find these elusive insects.

%d bloggers like this: