Nature Inquiries

by Carl Strang

One of the goals in my singing insects research this year was to get a better handle on two of the bush katydids, the broad-winged bush katydid and the Texas bush katydid (in the “W” years I was repeatedly amused by the fact that there is such a thing as a Texas bush katydid: nature nerd humor).

The above photo is of Scudderia texensis. I have found Texas bush katydids much easier to approach and photograph than broad-winged bush katydids (S. pistillata). During my recent trip to the U.P. I found one of the latter that held still long enough.

While the two look very similar to one another, the broad-winged is a distinctly smaller insect. Also, the wing proportions are different, as you can see roughly by comparing wing lengths to hind leg femur lengths in the above photos. This broad-winged is missing the end of its left forewing, but the longer hind wings are intact.

With such great camouflage, these katydids are not easy to find, and in survey work I want to identify them by song. Each of these species has two different songs, one very brief and one more extended. The more commonly produced songs, especially in daylight, are the short songs. To my ear the short songs of these two katydids are so similar that I remain uncertain about distinguishing them. These songs are very quick, lasting one-third to one-half second, and are series of 3-5 pulses. I think that the pulses of the Texas bush katydid may prove to be more distinct, like separate syllables: “dig-a-dig.” The pulses of the broad-winged may be more run together and with less of a raspy, more of a lisping quality.

In trying to sort this out I have been seeking the conditions in which these two insects sing their longer songs, which are very distinctive but less often produced. The Texas bush katydid sings its long song mainly at dusk. The song is like an extended version of the short song, lasting 3-4 seconds, dig-a-dig-a-dig-a-dig-a-dig, with the final syllable louder.

The broad-winged bush katydid is renowned for its long song, called its counting song. The elements of the song are lispy buzzes, each lasting a second or so. The remarkable thing is that these buzzes are grouped, and the buzzes increase in number from group to group as the song progresses. Within a group, buzzes follow one another immediately, with a few seconds between groups. A sequence might begin with a single buzz, followed by a group of two, then a group of four, then a group of 5 or 6. Commonly there are four groups in a song, but sometimes there are more. Then the katydid waits for a longer pause before starting a new sequence. Somewhat frustrating is my experience that the season in which broad-winged bush katydids sing their longer songs apparently is very brief in DuPage County. This year I went repeatedly to Springbrook Prairie Forest Preserve, after I first heard bush katydid short songs on July 20. At dusk on the evening of July 26 I heard only broad-wingeds singing counting songs. In 2008 I heard them at Blackwell on July 21. This year I heard them for the last time on August 2. On my next visit, August 7, there were none, and none on several visits thereafter. Though many nighttime singing insects extend their singing into the daytime later in the season, this does not seem true for the long songs of these two bush katydids in DuPage County. However, near the tip of the U.P. in late September, broad-wingeds were singing counting sequences in the late afternoon. It may or may not be significant that Texas bush katydids do not occur there.

This year I heard Texas bush katydid long songs only on August 6 and September 2. Last year I heard them on August 27 and September 2, and in 2007 on July 15 and October 4. So far, then, all years taken together, the season for long songs in DuPage County has been July 21 to August 2 for broad-wingeds, July 15 to October 4 for Texas bush katydids. The broad-winged’s season is longer, or at least later, farther north. And that’s where it stands. Lately all the short songs I am hearing have the distinct-syllable quality I associate with Texas bush katydids. Next year I will continue to sort out this puzzle.

Incidentally, there are other species of bush katydids in our area. One I’ll mention here is the curve-tailed bush katydid, S. curvicauda. It is more a forest edge species than the meadow-loving Texas and broad-winged bush katydids. Its songs are composed of loud rasping “zik!” syllables. Commonly it produces these in sets of three, but it also has simple counting sequences. Aside from the different sound quality, these differ from those of the broad-winged by having fewer groups (only 2-3 groups per sequence) and simpler sequences (2-3, 2-3-4, 3-3-4, etc.).

As always, you can find recordings of these various songs on line. I recommend the Singing Insects website  and the Songs of Insects website.