Luna Moth

Tails that fool bats

The luna moth (Actias luna) is a pale green giant silk moth with a long tail trailing from each hindwing. Those tails are decoys. Researchers used high-speed infrared video to watch luna moths spin their tails to deflect attacks by echolocating bats (hunters that find prey by the echoes of their own calls) away from the body and toward the tails. Tails lured bat attacks to themselves in 55% of encounters with intact moths, and moths with tails had a survival advantage of about 47% over moths whose tails were removed.

Four times over Long spatulate (spatula-shaped) tails have evolved independently four times in saturniid moths, the family of giant silk moths the luna belongs to.

A second study found that the tail echoes are weak compared with those of the wings and body. Their twisted shape, though, creates echoes that persist from every angle, which may make a bat misjudge where the moth is.

An adult with no appetite

The adult wingspan is 75 to 105 mm, about 3 to 4 inches. Adults have vestigial (leftover) mouthparts and do not feed, so they are short-lived. A new adult cuts its way out of the cocoon with serrated, chitinous spurs on its thorax, and it usually emerges in the morning, which allows time for its wings to expand and dry before the evening flight period.

A female releases a sex-attractant pheromone, a scent signal, and may attract males from a distance. Researchers identified its compounds, made them artificially, and found in field trials in Ontario and Kentucky that male moths were attracted to one of them on its own. Mating usually takes place during the first couple of hours after midnight.

A caterpillar that clicks

A full-grown caterpillar is bright green and 55 to 70 mm long. Its green coloration hides it, and when threatened it often rears up the front of its body in a “sphinx” pose. If attacked, it also makes a clicking noise with its mandibles, sometimes as a prelude to, or alongside, spitting up distasteful fluid. A study of clicking caterpillars found that luna caterpillars make airborne sounds upon attack, and that the sounds precede regurgitation.

The northernmost populations most often eat white birch. Farther south, caterpillars use a variety of host plants, particularly walnuts and hickories, sumacs, sweetgum and persimmon. Development from hatching to pupation takes a month or longer, depending on temperature.

Where it lives

The luna moth is usually found in forested areas. In southern Canada it occurs from Nova Scotia to Saskatchewan. In the United States it is found in every eastern state from Maine south to Florida, and west to eastern Texas and eastern North Dakota. Moths from southern populations tend to be smaller.