Insects of Indian Summer

By November most insects are either dead or hibernating, but some species, both native and alien, are aroused by the soft warmth of Indian summer.

Once again the fields and forests sing with a quieter rendition of the grasshopper-cricket-katydid chorus of late summer and early fall. Bristly great leopard moth and woolly bear caterpillars unfurl from their hibernation quarters under loose bark or hidden in plant materials and crawl across our veranda. An occasional alfalfa or cabbage butterfly flutters weakly over the fields. Swarms of midges dance up and down in the warmth of the setting sun. Hibernating Halloween ladybugs emerge to swarm around us as we sit on the veranda, soaking up the rays.

Every time I hear or see one of these insects so late in the season, I am especially appreciative of what seems almost magical. For a few days, I am reminded of all that was attractive in the world of summer because none of these stragglers bite or sting, not even the swarms of midges that seem to rise or fall according to their own rhythm.

Entomologists who have studied swarms of non-biting midges in the families Chironomidae and Cecidomyidae and mosquitoes understand how they swarm but disagree on why. They usually form swarms during periods of fairly rapid changes in light intensity, at sunset and sunrise. Reacting not only to light intensity but to certain temperatures, they fly upwind until they find a swarm marker for their species such as twigs of dead bushes, margins of ponds, or a light or dark spot. Then, according to entomologist Howard Ensign Evans in his classic book Life on a Little-Known Planet, “they allow themselves to be carried backward by the wind until they approach the leeward margin of the marker, whereupon they begin to control their flight again and finally once again fly upwind to the windward margin.” That maneuver is known as a “top swarm.”

“Free swarms” form over a flat surface without prominent landmarks, and “ceiling swarms” consist of many midges swarming high over a large area from which vertical columns of midges descend.

Entomologists disagree over whether the swarms are a mate-attracting behavior since the swarms usually consist almost entirely of males. But some researchers have watched females dart into the swarm where they are seized and mated. Others say little or no mating takes place.

The sound of their wings seems to bring midges together. If you talk or make noise near them, they are confused and only resume their normal flight when it is quiet again. Evans says, “the playing of a musical instrument to a dancing swarm can sometimes produce unusual effects, and a gunshot or loud whistle will often send them into wild disarray.”

I must admit that I have never tried this, but one entomologist–Erik Tetens Nielsen–learned to call down swarms by singing high C and high G. He also sent up a net attached to a hydrogen-filled balloon with which he captured a swarm. After studying many swarms in this way he concluded, “We do not know [why midges and mosquitoes swarm].”

Even in England such swarms were noticed long ago. Poet John Keats paid homage to them in his “To Autumn” when he wrote,

While barred clouds bloom in the soft-dying day,

And touch the stubble-plains with rosy hue;

Then in a wailful choir the small gnats mourn

Among the river shallows borne aloft

Or sinking as the light wind lives or dies…

At least one of the butterflies that survives to flutter through Indian summer would also have been familiar to Keats. The cabbage white or just plain cabbage butterfly (Pieris rapae) was introduced accidentally from Europe to North America in 1860. A small butterfly marked on its upper wing tip with black, the male has one black spot and the female two on their upper or forewings. Many people mistake these butterflies for moths because of their color and fluttery, floating, flight pattern.

Europeans call this butterfly the “small white,” but they, like us, recognize it as a species that favors the Mustard family. Its yellow-striped, green caterpillar eats cabbage, broccoli, radish, kale, collard, and cauliflower plants as well as over 20 species of wild plants such as winter cress, peppergrass, and, more recently, another alien, garlic mustard. In the Mid-Atlantic states, their new-found interest in garlic mustard has lured them, for the first time, from their customary open, weedy habitat to the forest in search of the plant.

The other late-flying butterfly, the alfalfa or orange sulphur (Colias eurytheme), comes from our own southwest. As alfalfa cultivation became common after the 1870s, this western species spread rapidly eastward, reaching the northeast in the 1930s. A yellow and orange butterfly that has multiple broods sometimes as late as November, it has been recorded as late as December 16 near Philadelphia. Warm spells often encourage its overwintering pupa to emerge prematurely so it is technically possible to see this butterfly long after its caterpillar food plants–alfalfa, vetches, and clovers–are finished. My latest date here is November 6, 1995, a day that dawned a cold, clear, 23 degrees after a spell of Indian summer.

Katydids, however, had only begun calling again that year on the second of November when the temperature hit 66 degrees and continued to rise. Grasshoppers and crickets, also members of the Order Orthoptera, only sing near noon on warm days. They vibrate their wings as if they are arthritic, but even if they are silent and hidden in the tall grasses of First Field, the vigilant male American kestrel dives down and catches them. Every autumn a male kestrel hangs out on our telephone wire and watches for what several studies indicate are their favorite foods. Last November, though, the kestrel only appeared when the days were warm and hazy to prey on the fading singers.

The same weather that re-started the Orthopteran singers also unfurled the bristly, curled balls of two closely related caterpillars already in hibernation. The woolly bear or black-ended bear caterpillar (Isia isabella) hibernates under a rock or log and is well-known in folklore for its ability to foretell the coming severity of the winter based on the size and color of its reddish-brown and black bands.

According to Eric Sloane in his Folklore of American Weather, “the wider the middle [reddish-brown] band the milder the winter.” Others disagree, saying that if the caterpillar is mostly reddish-brown, the winter will be very cold.

Still others base their prognosis of the weather on the lightness or darkness of the woolly-bears’ colors. If they are very light, the winter will be mild and short; if they are very dark, the winter will be severe.

Scientists, on the other hand, maintain that the color variations depend on the caterpillar’s age and that older caterpillars have more reddish-brown hairs.

The woolly bear caterpillar is a native species that changes into the yellow-brown Isabella tiger moth the following spring. Its close relative, another tiger moth, is called the great or giant leopard moth (Zeuzera pyrina) and was introduced from Europe before 1879. Like the woolly bear, it overwinters in caterpillar form but may come out on warm days. Covered with bristly black hairs, it reveals vivid red bands between its body segments when curled in a ball. It, too, changes into a striking moth, in this case, a white and black one with a three-inch wingspan and an orange-marked, blue abdomen.

None of the insects I have mentioned, though, are as ubiquitous in late fall and throughout the winter, as the Halloween ladybugs, especially if you live in a white, clapboard house as I do. From the moment they begin hatching in early October until the following spring, we have these ladybugs in our lives. They swarm on the veranda when they first hatch and make periodic appearances throughout the month before hibernating outdoors beneath leaf litter, under the loose bark of trees, or in clumps of grass.

But others prefer to move indoors. They are especially fond of old, white houses, probably because in eastern Asia they winter in the crevices of limestone cliffs.

This ladybug beetle species first appeared here in October of 1993 and is an Asian immigrant (Harmona axyridis). It arrived, probably by boat, sometime before 1988 when scientists discovered the first breeding population in St. Tammany Parish near New Orleans. By October 1994, wafted north by wind currents, the species had made it to Elmira, New York, a year after its arrival on our mountain.

Nicknamed the Halloween ladybug because of its orange color and the time of its swarming, the Entomological Society of America would like to rename it the “multicolored Asian lady beetle.” That name would emphasize its variable color scheme. Although most are yellow-orange, some are brick-red, and a few are even black with orange spots. Those ordinarily black spots not only vary in color but in numbers, ranging from few or no spots to as many as 20.

The ladybugs need cool hibernating places so those trapped in our warm living quarters won’t survive, the experts say. Maybe not, but they are lively enough, flying and crawling over windows, sinks, and my house plants. Sometimes several hundred appear on our bay window, and in my husband’s warm study, they swarm on every sunny day.

At first we thought they were cute, and I whimsically compared them to opossums because they roll over on their round, hard wing covers and play dead for several minutes after they are touched. Then they wriggle their legs, hoist themselves over on their stomachs and resume flying or crawling to wherever they are going. They are also prodigious predators on aphids and altogether a useful species.

On the other hand, scientists are afraid that this aggressive species will wipe out some of our native species of ladybugs. My own patience has worn thin over the past several winters as their numbers have burgeoned. Some days I vacuum them up by the hundreds, but they are quickly replaced by others.

“Ladybug, ladybug, fly away home” has become more than an old nursery rhyme to us as we fervently wish they would fly back to Asia where they came from. Instead, we watch this alien species take over our home every winter, giving us more communion with the insect world than we would like.