an annual cicada



August 29, 2010

Warm August and September evenings are filled with a chorus of strange sounds, with insects such as cicadas (often mistakenly called locusts), crickets and grasshoppers often predominating. Annual cicadas are mostly large, blackish insects with greenish markings and large, clear wings. They feed underground on tree roots for two to three years in their nymph stage before emerging as singing adults, but due to overlapping generations, we can hear some every year during late summer. Their loud buzzing sound is made only by males, and is produced by vibrating internal structures within their hollow drum-like abdomens.

Crickets sing at different tempos depending on their species and the temperature of their environment. Most species chirp more quickly the warmer the temperature (approximately 62 chirps a minute at 13°C in one common species). It is often possible to calculate the temperature in Fahrenheit by adding 40 to the number of chirps produced in 14 seconds. Crickets, like all other insects, take on the temperature of their surroundings, and as the temperature rises, their chemical reactions such as those involved in the muscle contractions used to produce chirping, occur more rapidly.

Only the male crickets chirp. A large vein running along the bottom of each wing has "teeth," much like a comb does. The chirping sound is created by running the top of one wing along the teeth at the bottom of the other wing. As he does this, the cricket holds its wings up and spread, so that the wing membranes can act as acoustical radiators.

It takes a bit of imagination to hear the “katydid..katydidn’t” song of the long-horned grasshopper that has been given that name. It is usually about two inches long and looks much like a green leaf with legs. It makes its sound by rubbing a scraper, which is the sharp edge of its front wing against a file found on the rough edge on the lower wing, a process much like that of the cricket. The male starts to sing from a chosen perch as darkness falls and the female’s “ears” that are situated on her forelegs direct her toward to the loudest singing male. An interesting research item is that the female can recognize her male counterpart only when they are at the same temperature.

We are not the only listeners to the insect chorus, as another interested party lingers at the edge of the woods. The Eastern screech owl is a small, nocturnal, woodland bird. It is only about 9 inches long and weighs about 7 oz., but it is a formidable hunter, out from dusk to dawn, but most active during the first four hours of darkness. When prey is spotted, the owl dives quickly and seizes it in its talons. Small prey will usually be swallowed whole on the spot, while larger objects are carried in the bill to a perch and then torn into pieces.

The male screech owl has a lower-pitched voice than the female. His most common call is a mellow, muted trill—each call lasting 2 to 3 seconds and consisting of about 35 notes, repeated at various intervals. A second more recognizable call is a descending whinny, often given during courtship, although we have been hearing it in the farmyard the past few nights. A mated pair will sometimes sing a duet consisting of both songs and also have been heard to bark or hoot at other times.

This little owl flies fairly rapidly with a steady wingbeat, rarely gliding or hovering, but may flutter with erratic movements when maneuvering through wooded areas. Its wings are broad and the head is held tucked in giving the bird a stubby appearance when flying. It is an opportunistic hunter and will attack any suitably-sized prey although the most favored are small rodents and deer mice. It will also hunt rats, chipmunks, squirrels, shrews, bats, and moles as well as any birds it can catch, and will gobble up large flying insects and anything else it considers edible.

Step out of doors after sunset and listen to the sounds of the evening. Another world awakens as darkness falls, and musicians tune up their instruments for our wonder and pleasure.