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Caterpillars

Caterpillars Eating & Molting

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.)

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Black Swallowtail Larvae Defending Themselves

7-8-19 black swallowtail larva 0U1A0103Caterpillars, 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.

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Woolly Bears Seeking Hibernacula

10-10-18 isabella tiger moth 119

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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Large Yellow Underwing Larvae Crawling On Snow

12-12-16-large-yellow-underwing049a2252The 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.

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Gypsy Moth Caterpillar Explosion

e-gypsy moth caterpillars 273The 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.

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Second Generation Calico Paint Moth Larvae Feeding & Resting

9-16-15 calico paint 111In the Northeast, Calico Paint Moths (Cucullia convexipennis), also called Brown-hooded Owlets, produce two generations a summer. The larvae of the first generation mature in July, and the second generation matures from late August into October. Calico Paint 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. The comparatively drab, brown adult moths they turn into can often be found on Wild Bergamot and Common Milkweed flowers in the early evening. (Thanks to Joan Waltermire for photo op.)

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Saddleback Caterpillars Preparing to Pupate

10-6-14 saddleback moth 006There is a group of moths (family Limacodidae) which are known as “slug caterpillar moths” due to the manner in which they travel during their larval stage, secreting a semi-fluid silk from their ventral pores as they move. These caterpillars come in all sizes and shapes. Among them is the Saddleback Caterpillar, which is much more colorful than the brown adult moth it eventually turns into. Saddleback Caterpillars are best known for their stinging (urticating) spines. Reputedly far worse than that of a bee, the sting of the Saddleback Caterpillar may be the most potent of any North American caterpillar. The larva’s bright colors serve to warn predators of its toxicity. Soon these caterpillars will be spinning cocoons (which can contain spines, as well) in which they will pupate until emerging as moths next spring. (Thanks to Rick Palumbo for photo op.)

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