Now is the time to be looking for the emergence of the most common silkmoth, Antheraea polyphemus from its cocoon. This large brown moth, commonly known as the Polyphemus moth, is named after the giant in Homer’s epic poem, “The Odyssey”. Unlike the mythological man-eating Polyphemus, this moth never feeds as an adult and has multiple generations per year.
Polyphemus cocoons, which are about 1.5 inches-long, are found hanging from branches or on the ground beneath several trees, including oak, hickory, maple, walnut, sycamore, willow, elms, etc. An outer layer of tree leaves surrounds the cocoon, which is composed of gray silk. Inside the cocoon is the pupa. In April and May, the large moth exits the cocoon in late afternoon and mates the same day. To locate these large moths, look near lights.
Polyphemus moths have a 3.5 to 5.5 inch wingspan with distinctive markings. Each front wing has an oval spot edged in white and black. Larger spots occur within a dark region on each hindwing. Near the edge of each wing there is a black line bordered by white. Large, feathery antennae are also present on moths. Many images of Polyphemus and other silkmoths can be found online.
Antheraea polyphemus moths do not cause feeding damage. After mating, females lay eggs singly on the underside of tree leaves. In summer, newly- hatched Polyphemus caterpillars consume their eggshells and are found singly rather than in groups. At maturity, the bright green caterpillars are about three inches long with a brown head (Figure 1). On each caterpillar segment, six bristles are visible from yellowish-orange tubercles (small swellings). Also, a slanted yellow line occurs on nearly all body segments. Caterpillars feed on tree foliage, with older ones consuming an entire leaf before cutting the petiole, causing the leaf to drop.
Polyphemus caterpillars produce clicking sounds from their serrated mandibles (mouthparts) when gently prodded. Caterpillars commonly click 50 to 55 times, lasting over a minute when attacked by a predator. This defensive response is also commonly followed by regurgitation to ward off birds or mammals. The fluid is thought to gum up the mouthparts of the attacker or it may contain chemical compounds that make the caterpillar distasteful. Following regurgitation, caterpillars attempt to re-imbibe this fluid in preparation for another attack.
Another large green caterpillar, Hyalophora cecropia, can be found on apple, plum, cherry, walnut, elderberry, maple, ash, willow, elm, box elder, poplar, and lilac from April to August in Missouri. The adult is commonly known as the Cecropia moth. In contrast to Antheraea polyphemus, Cecropia moths are dark brown with four white crescent-shaped spots near the center of the wings and two black oval-shaped spots on the tips of the forewings. It is the largest moth found in North America with a wingspan of five to seven inches. Cecropia moths produce one generation per year. Female moths produce pheromones, which are detected by the male’s feathery antennae up to a one mile distance. After mating, each female may lay up to 100 eggs that hatch in 10 to 14 days, producing tiny black caterpillars that feed in groups on tree and shrub foliage during summer. As caterpillars mature, they change from black to yellow with many black bristles. By August, caterpillars are up to four inches long and are green (Figure 2). Near the head, there are four orange-red tubercles or “knobs” with black bristles. Behind these tubercles, caterpillars have paired yellow tubercles with black spines their body segments. On the sides of their body, there are also light blue tubercles occurring on each segment. In the early fall, Cecropia caterpillars spin a three inch-long cocoon attached to a twig and overwinter as pupae.
These two species of caterpillars don’t usually cause excessive damage to plants and thus, chemical control is unnecessary in most cases. With a keen eye, you can spot the various life stages of these common silk moths in your area.
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REVISEMarch 29, 2016