One of the last things one might expect to see on a newly-exposed grassy field in the middle of March is a caterpillar crawling along. This would be unexpected because most moths overwinter as eggs or pupae inside cocoons, not as caterpillars (larvae). Most moths, but not all. Some species of moths overwinter as larvae (and adults).
Tiger Moths (and Tussock Moths) overwinter as caterpillars and pupate in the spring before emerging as adults during the summer. One member of the Tiger Moth group that is familiar to many is the Isabella Tiger Moth, known as the Woolly Bear (Pyrrharctia isabella) in its larval stage. Another member of this group that overwinters as a caterpillar is the Great Tiger Moth (Arctia caja). As early as mid-March you can find both of these caterpillars wandering in search of a protected spot where they will form hairy cocoons that surround and protect their pupal cases. The pictured Tiger Moth adult (Great or Garden Tiger Moth) bears the white geometric stripes that give the members of this group their common name.
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The Gypsy Moth (Lymantria dispar dispar) was introduced to North America from France by E.L Trouvelot in 1869 who had hopes of breeding a silk-spinning caterpillar that was more resistant to disease than the domesticated silkworm. Unfortunately, the caterpillars escaped into his backyard. About 10 years later, they began to appear in large swarms, and by the late 1880s they were causing severe defoliation in the area. Since then the Gypsy Moth has become one of the most destructive pests of hardwood trees in the eastern U.S.
The adult female moths emerged from their pupae this summer. With a life span of one week, the adults do not feed; they do, however, mate and lay eggs. Although the female moth has fully formed wings, she cannot fly. She emits pheromones that attract males, mates and then lays a cluster of 75-1,000 eggs close to where she pupated. She then covers them with buff-colored, hairlike setae from her abdomen, which serve as protection from predators and parasites. The eggs overwinter and hatch in the spring. The larvae have a voracious appetite and feed on more than 300 species of trees and shrubs.
Gypsy Moth egg masses appear to be prolific this fall, perhaps because there has been no significant wet weather to fuel the fungus (Entomophaga maimaiga) that feeds on the Gypsy Moth. While there are other natural controls for Gypsy Moths (birds, squirrels, mice, etc.) they don’t prevent infestations. If you wish to rid your woodlot of these caterpillars, you can remove the egg masses and pour boiling water over them. Scraping the eggs onto the ground is less effective as they can survive temperatures of 20°- 30°F. degrees below zero.
It’s hard to believe, but this fuschia-colored caterpillar is going to emerge from its cocoon next spring as a relatively dull black and white moth called the White-blotched Heterocampa (Heterocampa umbrata). These caterpillars have two shiny knobs behind their head which are the remnants of “antlers” that the caterpillars have during their first instar. White-blotched Heterocampa larvae change color as they mature and develop. At any given stage, a caterpillar could be purple and fuchsia, or brown and tan or green and white; it is not unusual for them to be mistaken for three different species. The caterpillars can be found feeding on oak leaves. Look for the adult woodland moths at night, when they are attracted to lights. (Thanks to Lily Piper Brown who found two of these amazing caterpillars recently, and her mother, Sadie Brown, who photographed this one.)
The large, green swallow-tailed moth known as the Luna Moth (Actias luna) is familiar to many. Its short life of about a week begins in June when it emerges from its cocoon, mates, lays eggs and then dies. The larval stage of this giant silk moth is not as well known, but has just as striking an appearance as the adult moth. It is an unforgettable lime-green with tiny magenta spots along its length.
When threatened by a predator, Luna Moth caterpillars have several defensive behaviors, including emitting clicks as a warning and regurgitating the contents of their intestine, both of which have proved to be effective deterrents. Look for these caterpillars on their host trees which include birch, hickory and walnut. (Thanks to Susan and Dean Greenberg for photo op.)
Because yellowjackets do not produce or store honey one might wonder why striped skunks, raccoons and black bears frequently dig up their underground nests. It is the young yellowjackets (larvae), not honey, that is so highly prized by these insect-eating predators. At this time of year it is crucial for them, especially black bears who go for months without eating or drinking during hibernation, to consume enough protein to survive the winter.
Whereas adult yellowjackets consume sugary sources of food such as fruit and nectar, larvae feed on insects, meat and fish masticated by the adult workers that feed them. This makes the larvae a highly desirable, protein-rich source of food. (Yellowjacket larvae reciprocate the favor of being fed by secreting a sugary material that the adults eat.)
Three to five thousand adult yellowjackets can inhabit a nest, along with ten to fifteen thousand larvae. Predators take advantage of this by raiding the nests before frost kills both the adults (except for fertilized young queens) and larvae in the fall. Yellowjackets are most active during the day and return to their underground nest at night. Thus, animals that raid them at night, such as raccoons, striped skunks and black bears, are usually very successful in obtaining a large meal. Occasionally, as in this photo, the yellowjackets manage to drive off predators with their stings, leaving their nest intact, but more often than not the nest is destroyed and the inhabitants eaten. (Thanks to Jody Crosby for photo op of yellowjacket nest (circled in red) dug up by a black bear – note size of rock unearthed.)
In the Northeast, Brown-hooded Owlet moths (Cucullia convexipennis) produce two generations a summer. The larvae of the first generation mature in July, and the second generation matures from late August into October. Brown-hooded Owlet larvae are often found on aster and goldenrod plants, resting on stems (often head down) in plain sight during the day. First generation larvae feed on the leaves and the second generation consumes the flowers of these plants. (Photo: note molted skin above caterpillar.)
American Dagger Moth (Acronicta americana) caterpillars are present from June to October in the Northeast, but because of their size (up to 2 ½”) and their searching for a suitable site to pupate in over the winter, they are very evident right now.
American Dagger Moth caterpillars have lemon yellow (early instars) or white (late instars) setae, or hairs. Their distinctive characteristic is the pattern of black tufts: two pairs of diverging tufts along the middle of the caterpillar and one thick black tuft at the end. As larvae they have a wide variety of host trees, including alders, ashes, birches, elms, hickories, maples, oaks, poplars, walnuts, and willows.
After locating a wintering site, these caterpillars will spin a cocoon in which they will spend the next several months as pupae. Late next spring American Dagger Moths will emerge from their cocoons as two-inch-long brown moths.
If touched, these caterpillars can cause a mild allergic reaction (a rash) in some people who touch the them.
The larval stage of a butterfly or moth is spent doing little but eating. Only as a caterpillar will these insects have chewing mouthparts, and they waste no time in using them. As they eat, caterpillars increase in size and their skin (exoskeleton) becomes tighter and tighter, as it doesn’t grow larger. The caterpillar grows a new, larger exoskeleton underneath the outer skin and then sheds, or molts, the old one. Most caterpillars molt five times. At first, the new exoskeleton is very soft and not very protective, but it soon hardens. The shed exoskeleton is often eaten before the caterpillar ingests more plant food.
There are names for the caterpillar’s stage of development in between each molt, called “instars.” When the caterpillar hatches from its egg, it is referred to as a “first instar” caterpillar. After its first molt, the caterpillar is referred to as a “second instar,” and so on up until the exoskeleton is shed for the final time, revealing the chrysalis (if it’s a butterfly).
The Monarch in the photograph is a very new 4th instar instar caterpillar (see antennae which haven’t hardened). It has shed three times. Its third exoskeleton (which it has just shed) is on the milkweed leaf behind the caterpillar. To see a real-time video of a Monarch molting go to https://www.youtube.com/watch?v=EbHyq3RwtxI.
(Thanks to Otis Brown for his keen eye in finding this Monarch caterpillar before it ate its just-molted skin. Also to Ba Rea ((www.basrelief.org) for her instar confirmation.)
Caterpillars, the larval stage of moths and butterflies, are very susceptible to predators (escaping quickly is not an option). Much of their energy in this stage is devoted to defense mechanisms to thwart would-be predators. A partial list of these defenses includes irritating bristles with detachable tips (Tussock Moths), toxic “breath” (Tobacco Hornworms, consumers of tomato plants, tobacco and other plants in the nightshade family, release toxic, bad-smelling nicotine), toxic bodies (Monarchs) and anti-coagulant venom (Giant Silkworm Moths).
Black Swallowtail (Papilio polyxenes) larvae defense mechanism strategies change as they develop. In early stages, or instars, they mimic bird droppings (not an appealing meal for most predators) and older larvae possess bright yellow-orange, horn-like organs behind the head known as osmeteria (see photo inset). When threatened, larvae rear up, extrude the osmeterium, and attempt to smear potential predators with a chemical repellent.
Black Swallowtail larvae are frequently sought after by parasitoids, which can locate their hosts by chemicals in the hosts’ feces (frass). To decrease their chances of being parasitized, Black Swallowtail larvae toss their fecal pellets away from themselves with their mandibles.
To learn much more about both moth and butterfly larvae, go to http://www.thecaterpillarlab.org.
Looking every bit like the Golden Alexander (Zizia aurea) flower buds on which they were laid, the pale yellow eggs of a Black Swallowtail (Papilio polyxenes) are next to impossible to find unless one is fortunate enough to see them in the act of being laid. Members of the parsley family (Golden Alexander, Wild Parsnip, Queen Anne’s Lace, Dill, Carrot) are host plants for most ravenous Black Swallowtail larvae, and thus that is where you will find their eggs. As they eat, the caterpillars absorb toxins from their host plant, which does not harm them but makes them distasteful to avian predators.
The Isabella Tiger Moth typically has two broods during the summer. The caterpillars (Woolly Bears) in the first brood pupate and emerge as adult moths mid-summer. The second brood overwinters as caterpillars and pupate in the spring. The Woolly Bears we see crossing roads at this time of year are second-brood caterpillars in search of protective hibernation sites (hibernacula).
Old-timers predicted the severity of the coming winter by the relative lengths of the black and brown bands of the caterpillars when they became easy to observe in the fall – the longer the black sections and narrower the brown section, the harder a winter they were in for. In fact, this may have had some validity, as brown hairs (setae) are added to the middle band every time the caterpillar molts. Therefore, the older the caterpillar, the wider the brown band. If winter comes early, the caterpillar’s brown band would be relatively narrow due to the fact it didn’t have time to mature fully and develop a wider brown section before hibernating.
The adult stage of the Isabella Tiger Moth is often overlooked, due to the appeal of the larval stage. This tan moth, with a wingspan of 1 ½ – 2 inches, has tiny black markings on its wings. Male and female are sexually dimorphic and can be distinguished by the color of their hind wings. Males have yellow-pale orange hind wings while the hind wings of females are rosy. (Photo: Woolly Bear; photo inset: female Isabella Tiger Moth)
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The larvae of moths in the family Geometridae (the second largest family of moths in North America) are known as loopers, inchworms and spanworms. These names are derived from the looping gait of the caterpillars. They generally have only two or three pairs of prolegs (at the hind end) rather than the usual five pairs of most moth and butterfly larvae. The lack of prolegs in the middle of their body causes them to move by pulling the hind prolegs up to the true legs on the thorax in the front of their body, thereby forming a loop, and then extending the body forward.
Many Geometrid caterpillars evade predators by flinging themselves from trees and dangling by a silk thread that is attached to the tree at the other end (see photo). After the danger passes, they climb back up the silk and return to their leaf-eating.
When it comes to ingenuity, the Golden Tortoise Beetle (Charidotella sexpunctata) larva has all others beat! Instead of discarding its feces, it collects them and uses them as a means of chemical protection. Golden Tortoise Beetle larvae have a “fecal fork” on their last abdominal segment which they hold over their body. They also possess a muscular, telescopic anus which they can manipulate in such a manner as to deposit their feces onto their fecal fork. Bits of shed exoskeleton combined with days of feces accumulate on this fork and create an effective fecal shield. Golden Tortoise Beetle feces contain alkaloids from the plants that they’ve eaten (Bindweed and other plants in the family Convolvulaceae) and consequently the shield wards off predators. (Photo: Golden Tortoise Beetle larva with fecal shield; inset – adult Golden Tortoise Beetle)
The striped caterpillar that is crawling along the surface of fresh snow is the larval stage of a noctuid or owlet moth known as the Large Yellow Underwing (Noctua pronuba). Noctuids are dull-colored, medium-sized, nocturnal moths that are attracted to lights in the summer. They usually possess a well-developed proboscis (mouthpart) for sucking nectar. The Large Yellow Underwing larva is one of many species known as cutworms that feed on herbaceous plants. Introduced from Europe to Nova Scotia in 1979, this species has since spread north to the Arctic Ocean, west to the Pacific, and south to the Gulf of Mexico.
Larvae sporadically feed through the winter months whenever temperatures are above the mid-40s. The Large Yellow Underwing larva has been nicknamed the winter cutworm and the snow cut-worm for its ability to feed actively when other cutworms are dormant for the winter. Occasionally on warmer winter days, such as we had last week, you see them crawling on the snow.
The Gypsy Moth was introduced into the United States in 1869 by a French scientist living in Massachusetts. Since then its range has expanded to include the entire Northeast south to North Carolina and as far west as Minnesota and Iowa. The consequence of the introduction of this insect is staggering. According to the U.S. Dept. of Agriculture, since 1980, the Gypsy Moth has defoliated close to a million or more forested acres each year. In 1981, a record 12.9 million acres were defoliated. This is an area larger than Rhode Island, Massachusetts, and Connecticut combined.
The Gypsy Moth females lay their eggs, usually on host tree trunks, in late summer. The eggs overwinter and hatch in the spring. Gypsy Moth caterpillars feed on a variety of species of shrubs and trees, with White Oak being their preferred host, metamorphose, mate and repeat this process. Usually their numbers are not overwhelming, but due to the weather conditions we’ve been experiencing, the caterpillar population has skyrocketed in some areas, especially in southern New England.
Conditions were very dry in parts of New England in May 2014 and May 2015, which impeded the growth of a certain kind of Japanese fungus (Entomophaga maimaiga) that keeps the Gypsy Moth caterpillar population under control. Without this fungus present to keep their numbers in check, Gypsy Moths have flourished. Although there was some rain this spring, there were many areas that did not get enough to benefit the fungus, and in these areas, trees are now stripped of their leaves. It is possible in places in southern New England to track the pattern of rainfall simply by looking at where trees are still in full leaf. Fortunately, the time has come for Gypsy Moth caterpillars to pupate, so most of this year’s destruction has already occurred. Here’s hoping for a rainy May next year.