Nature Notes: Trains, Planes, Crickets
The weather people tell us we are in the dog days of summer. It is not surprising, then, to hear at the day’s hottest point a piercing whine, the likes of which you might have woken up to on an October Sunday morning when the gasoline-powered leaf blowers start in. But in these boiling-hot days, that sound is not a leaf blower but the dog day harvest fly, or dog day cicada, perhaps the loudest of all insects in North America.
As we approach the perennially hottest month, August, the members of the Orthoptera, the “straight wings” — grasshoppers, katydids, tree crickets, and cicadas — begin to announce their individual identities. The birds stop singing and the insects take over the domain of sound, especially at night. The night singers often begin their annual stridulating sessions, wing against wing, during the day, and that is why on Monday at 12:30 p.m., when the thermometer registered a very humid 87 degrees in Noyac, they uncased their instruments and started in.
They were warming up for the first night of chorusing in 2011, which would have started about eight hours later at dusk, except for the fact that a storm swept through and wetted down the vegetation. So they started in earnest the next night when it was hotter and the moon was waning and there was no wind to compete with. These were the snow tree crickets.
Fifteen years ago during the evening of the fated TWA midair explosion, they started in on almost the same date. They haven’t missed that start time, give or take a day or two, at least not in Noyac, since then. It should be a resounding year for them locally. The trees and shrubs are full of leaves, hardly a gypsy moth caterpillar or canker worm around to eat them, but plenty of aphids, their primary fare.
It looks like they’ll have the nights to themselves for a while, as the tree crickets’ biggest competitors, the katydids, are thus far silent. The katydid’s “Katy did, Katy didn’t” repetitive song can go on for hours with hardly a pause. It’s much lower in pitch than the tree crickets’ pulsing tremolos, but can be as loud and just as persistent. It’s the male katydids and male tree crickets that do the singing, one pair of wings called the tegmina, have toothed inner edges that generate the songs when rapidly rubbed together.
The pitch of the songs is temperature dependent. When the evening temperatures fall in September, the pitch can fall an octave or more and the speed of delivery slows to a crawl. There is another major difference between the two calls. Early American naturalists determined that one can almost gauge the air temperature by counting the number of tree cricket pulses per unit time. If you count the number of pulses in 13 seconds and add 40 to it, you have the temperature in Fahrenheit within a degree or two.
Not so for the katydid. I’ve tried on numerous occasions to equate katydid rate of delivery with temperature and have never come close.
Who among us carries a thermometer around when we are out hiking or camping? Who among us doesn’t carry a timepiece on us at all times? Cellphones give us the time but generally not the temperature. Next time you’re walking in the woods at night or tented out in the dark during August, count the number of tree cricket pulses in 13 seconds, add it to 40 (no need for a calculator) and, voila, you have the night temperature. Hopefully, you’ll have your answer in less than five minutes. If you want it in Celsius, well that’s an entirely different matter.