As the weather cools, the nocturnal chorus of insects gradually fades across the Vineyard. Among the hardiest singers are the tree crickets, an unusual subfamily that can fend off the cold until deep into November. While almost unknown among humans, this group boasts some very common members. You’ve surely heard their songs, even if you didn’t know it.
You’d never imagine that these insects are close relatives of the robust black field crickets that chirp in yards and basements. Tree cricket species vary somewhat in color, but all are pale nearly to the point of translucence. Their bodies, about an inch long, are elongated; their long legs stretch outward into a flattened stance. On males, the forewings (which produce the remarkable songs) are more or less broad and hardened, like cellophane, for resonance; wings on females are narrower and softer. On females, a short, dark spike called an ovipositor extends from the abdomen; it’s used to lay eggs by injecting them into the stems of plants, where they overwinter until hatching the following spring.
Both sexes fly, but laboriously. For locomotion, tree crickets rely mainly on a lizard-like crawl along branches, or, when in a hurry, on powerful leaps impelled by the long hind legs. While some orthoptera seem to jump at random, tree crickets take careful aim and launch themselves on a fast, flat trajectory, hitting their targets like well-aimed artillery shells. Their broad stance allows them to latch on like Velcro when they land.
Like most orthoptera, tree crickets are omnivorous, but their feeding habits are said to lean toward the predatory: While they eat leaves, the bulk of their diet reportedly consists of smaller, soft-bodied insects, with aphids a particular favorite. For this reason, tree crickets can be considered helpful to the human gardener. You’ll rarely see a tree cricket on the ground; while one of our species evidently prefers herbaceous vegetation, in general tree crickets live and sing in shrubs and bushes.
As befits such odd-looking creatures, tree crickets have evolved a bizarre procedure for mating. The first part — a male, vibrating his wings to attract a female — is pretty standard among crickets and katydids. But as the male “sings,” an approaching female takes advantage of his raised wings to drink a secretion produced by glands exposed on the male’s back. While she is thus occupied, the male slyly transfers a tiny round membrane filled with his sperm, called a “spermatophore,” from the tip of his own abdomen to the tip of the female’s.
Given time, sperm eventually make their way from the spermatophore into the female’s reproductive tract, fertilizing her eggs. But given the opportunity, the female will eat the spermatophore, which represents a highly nutritious meal. This, obviously, prevents the male from passing along his genes. So the male continues desperately singing, offering up his song and his succulent back secretions to distract the female from dining on the spermatophore.
Evolutionarily speaking, the purpose is clear. In order to successfully fertilize a female, a male tree cricket needs to be in prime shape, equipped with reserves to keep his secretions flowing and sustain his energy-intensive singing for long enough for the spermatophore to empty. These bizarre gymnastics ensure that only the healthiest males succeed in passing along their genes.
So far, I’ve documented five types of tree crickets on the Vineyard. In a different genus from the other four, two-spotted tree crickets are pink in color and sing a sustained, dry buzz. They are common, even or perhaps especially in settled areas. Also very common is the snowy tree cricket, which sings a series of short, liquid pulses or chirps lasting about a second each. The narrow-winged tree cricket, somewhat less numerous, sings soft trills several seconds in duration. Davis’s (with a song much like the narrow-winged) and four-spotted (singing a long, rich trill) tree crickets are both known on the Vineyard only from one or two records, suggesting they are uncommon here.
Tree crickets can be reliably identified by their songs, but visually, most of our species are similar enough to pose a stiff identification challenge. The presence, absence, or extent of pale orange coloration on the head is of some help. But happily, one trick works without fail to identify these crickets: The basal segments of the antennae of each species bear a distinctive pattern of tiny black dots. “Tiny” is the operative word here; these dots are mere specks, and it takes magnification or at least a very, very close look to discern them. But just a glimpse suffices for a firm ID.
Like many orthoptera, tree crickets are well camouflaged and fiendishly good at keeping themselves hidden. (One hint for searching: Look for their long, thread-like antennae rather than for their bodies, which are almost always on the opposite side of a branch from your eyes.) But the songs of the more common species can be heard widely across the Vineyard, and you’ve still got a few weeks left to appreciate their talents.