The Tiny Ones

by Carl Strang

One of my goals this year was to achieve some clarity with two of the tiniest singing insects in the Chicago region. The variegated ground cricket (Neonemobius variegatus) and Cuban ground cricket (N. cubensis) are only a quarter to a third of an inch long. They are so unobtrusive, with their low-volume trills and hidden haunts, that you have to listen for them even to know they are around. Both species have rapid trills with crescendo starts, and unless you have perfect pitch and better hearing than me, telling their songs apart means working from sound recordings and getting technical.

Variegated ground cricket

Cuban ground cricket

My accumulated recordings of Neonemobius songs fall into two clusters, demarcated by a space that has remained remarkably consistent.

The dots in this graph each represent a recording of a Neonemobius cricket song, analyzed in the computer. The pulses represent the speed at which the cricket rubs his wings together to produce the song, and the frequency is the highness or lowness of the song’s pitch. Both measures increase with temperature. Note that variegated ground cricket songs fall into the upper left portion of the graph, Cuban ground cricket songs lower right. Dashed lines are my eyeball estimates of the space between the two clusters of points.

Variegated ground crickets vibrate their wings more slowly than Cuban ground crickets, yet have higher-pitched songs at a given temperature. This was the tentative conclusion I had drawn, but I needed some validation, and got it in October.

Here I have to back up a bit. I had found variegated ground crickets in the Chicago region, and would not have considered the possibility of Cuban ground crickets without the work of Lisa Rainsong. Cuban ground crickets had been known as a southern species until Lisa found them to be abundant in Cleveland. Her discovery alerted me to the possibility that they also might have reached the Chicago region. That possibility was realized when I found Cuban ground crickets in Gar Creek Forest Preserve in Kankakee County, Illinois. A captive Gar Creek Cuban ground cricket anchored the right-hand portion of the graph (yellow dots, yellow line).

A few observations of variegated ground crickets in previous years fell into the left-hand cluster, but I needed more. This year a captive variegated ground cricket from Gar Creek, which has both species, provided a series of recordings at various temperatures which fell as expected (red dots, red line).

Early in October I visited Lisa and her partner Wendy Partridge, and they showed me an area where Cuban ground crickets are abundant.

This meadow in the North Chagrin Reservation, a Cleveland Metroparks site, is packed with Cuban ground crickets. Lisa and Wendy check out tree crickets down the trail.

My recordings of two individuals at that site fit nicely into the previously established Cuban ground cricket cluster (green dots).

The final touch for 2018 came on October 18. I had 3 recordings, from 2006-2018, from north Blackwell Forest Preserve in DuPage County, all of which fit into the Cuban ground cricket cluster. Despite a few frosty nights, Neonemobius crickets had survived and were singing. I succeeded in flushing out one of these, and he was indeed a Cuban ground cricket. I regard this as a final validation of the graph. Now I need to go back to most of the 22 counties of the Chicago region in future years, and discover where each of these two species occurs.

Revised distribution of variegated ground crickets in the Chicago region, based mainly on analysis of sound recordings.

Revised distribution of Cuban ground crickets. One or both of the two species occur in every county, but I have not yet made sound recordings everywhere I heard Neonemobius crickets singing.

This story is an excellent example of hidden surprises that are waiting for researchers to uncover.

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Sound Ideas: Variegated and Cuban Ground Crickets

by Carl Strang

One of the highlights of the field season just past was finding variegated ground crickets, a long sought species, right under my nose, as described earlier.

Variegated ground cricket

Variegated ground cricket

Here is a recording I made in 2011 in the lawn at Mayslake Forest Preserve. I have trimmed out all but the critical end portion, which includes the abrupt end of one trill and the crescendo beginning of another:

I had made the incorrect assumption that these crickets, living in cracks and holes in the lawn, were Say’s trigs. Here is a recording of one of the trigs from nearby Fullersburg Woods Forest Preserve. The ending likewise is abrupt, but the next trill has a “chuwee” beginning.

In both cases the trills are extended, longer in the trig as a rule. A third species worth comparing here is the Cuban ground cricket. I have not encountered this species in the Chicago region, yet, but I need to be alert for it. Previously known only as a southern species, Lisa Rainsong has found it to be common in the Cleveland area. Ecologically it seems to resemble the variegated ground cricket in liking wet areas near lakes, rivers, and marshes, but is active on the surface rather than remaining out of sight in gravel or in soil crevices. Here is a partial recording of a Cuban ground cricket living in a terrarium in Lisa’s home:

The repeated brief scratches or chirps are from a striped ground cricket in another terrarium. The Cuban ground cricket, a member of the same genus as the variegated, likewise has a crescendo beginning, an extended high-pitched trill, and an abrupt ending. The pitch is just a little lower than that of the variegated, but otherwise they are much the same.

A final note on this topic is that my analysis allowed me to identify a recording from Illinois Beach State Park as belonging to a variegated ground cricket.

The singer was located beneath this vegetation, a few steps from the Dead River. I could not find it, and now realize that it must have been beneath the surface.

The singer was located beneath this vegetation, a few steps from the Dead River. I could not find it, and now realize that it must have been beneath the surface.

Here is an excerpt from the recording (you may need to turn up the volume):

All of this has me primed to document variegated ground crickets elsewhere in the coming season, and to be alert for Cuban ground crickets.

 

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.

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