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Metamorphosis

Brachonid Wasps Pupating and Emerging

8-29-14 brachonid wasps 010Tobacco Hornworms, Manduca sexta (often found feeding on tomato plants and confused with Tomato Hornworms, Manduca quinquemaculata) are often the target of a species of a Brachonid wasp (Cotesia congregata) that parasitizes beetle, moth, fly and sawfly larvae. The adult wasp lays her eggs inside the hornworm with her long ovipositor. The eggs hatch and the wasp larvae feed on the caterpillar. Eventually the wasp larvae emerge and spin silk pupa cases (cocoons) on the skin of the dying hornworm caterpillar, inside of which they transform into winged adults within four to eight days. Brachonid wasps are extremely good at locating hornworms, even when there are very few to find. Because they parasitize hornworm, cabbage worm, aphid and gypsy moth larvae, Brachonid wasps are considered important biological control agents. If you want to discourage Tobacco Hornworms in your tomato patch, allow the wasps to complete their metamorphosis – this accomplishes both the demise of the hornworm, as well as an increased population of Brachonid wasps. (Thanks to Emily and Joe Silver for photo op.)

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Second Brood of Woolly Bears Hatches

8-18-14  woolly bear 093Typically we start seeing Woolly Bear caterpillars in October, when they are searching for sheltered spots in which to spend the winter as larvae. With only two months between now and then, it came as a surprise when my great nephew and budding naturalist Eli Holland discovered a very young Woolly Bear recently. It turns out that in New England, there are two broods of Isabella Tiger Moths (whose larval stage is the Woolly Bear). The caterpillars that hibernated last winter emerged from hibernation this past spring, pupated, transformed into adult Isabella Tiger Moths, and proceeded to mate and lay eggs. It is these eggs that have recently hatched, and the Woolly Bear caterpillars that are no bigger than the length of your baby fingernail right now will be eating dandelions, grasses, nettle and meadowsweet nonstop for the next two months in order to survive the coming winter.

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Caterpillars Molting

6-25-14 caterpillar molting 044A caterpillar is the larval stage of a moth or butterfly. It is the only stage that has chewing mouthparts, and therefore a caterpillar spends most of its waking hours eating. This consumption of food results in massive growth, making its skin/exoskeleton very tight. When this happens, a hormone called ecdysone is produced, prompting the caterpillar to molt, losing its old exoskeleton (to left of caterpillar in photo) under which is a new and larger exoskeleton. After the molt, while the new exoskeleton is still soft, the caterpillar swallows a lot of air, which expands its body. Then, when the exoskeleton hardens, it lets the air out and has room for growth. Caterpillars molt four or five times as they grow. Each different caterpillar stage is called an instar. (Photo: Forest Tent Caterpillar)

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Eastern Tent Caterpillars Hatching & Building Tents

eastern tent cat. FINAL 090The adult Eastern Tent Caterpillar moth lays her eggs in late spring or early summer on a tree whose leaves its larvae will eat (black cherry and apple trees are favorites). Two to three hundred eggs are deposited in a mass that encircles a thin branch. Within three weeks fully formed caterpillars develop inside the eggs. The caterpillars remain there until the following spring, when they chew their way out of the eggs just as the buds of the host tree are starting to open. As soon as the caterpillars emerge, they construct a silk tent within which they reside, enlarging it as they grow in size.

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Promethea Moth Cocoon

4-22-14  promethea cocoon 478When a Promethea Moth caterpillar, one of our giant silk moths, is ready to pupate at the end of the summer, it strengthens the stem, or petiole, of a leaf on its host plant with silk and then attaches the silk to a nearby branch, assuring that the leaf will remain attached to the tree. (Imagine having the instinctive foresight in your youth that this caterpillar had!) The caterpillar then curls the leaf around itself and spins its cocoon inside the curled leaf. The cocoon dangles from the host plant throughout the winter and in early summer the moth emerges. Now is the perfect time for finding a Promethea Moth cocoon, as last year’s leaves are gone on most trees, and this year’s buds have yet to open. Look for a tree or shrub that has just one dead leaf hanging from one of its branches. (Cecropia caterpillars favor black cherry, poplar, ash, maple, oak and willows trees among others.)

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Cecropia Moths Pupating

11-11-13 cecropia cocoon dissected  056Our largest North American native moth, the Cecropia Moth, Hyalophora cecropia, spends the winter as a pupa inside a cleverly-crafted 3” – 4”-long shelter, or cocoon, which it creates and attaches lengthwise to a branch while still in its larval stage. The Cecropia caterpillar, with the silk glands located near its mouthparts, spins not one, but two silk cases, one inside the other. In between the two cases, it spins many loose strands of very soft silk, presumably to enhance the insulating properties of the cocoon. Inside the inner case, the caterpillar splits its skin and transforms into a pupa. Come spring, an adult moth will emerge from the pupal case and exit the cocoon through one end which was intentionally spun more loosely, allowing the moth to crawl out the somewhat flexible tip. (Note: dissected cocoon was not viable.)

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Bruce Spanworms Emerging & Mating

11-7-13 winter moth IMG_4880I try not to repeat post topics, but in the past two days the sudden emergence of inch-long, tan moths in the woods has been so dramatic that I couldn’t not mention them. These ghost-like, light tan moths are referred to by entomologists as Bruce Spanworm moths, Operophtera bruceata, named after an entomologist by the name of Mr. Bruce. They are often called Winter Moths, due to the fact that they are one of the latest moths to be seen flying, as well as Hunter Moths, as they share the woods with hunters at this time of year. From October to December Bruce Spanworm moths emerge, mate and lay eggs. While this timing is unusual, it makes sense when you think about it — many birds, their primary predators, have left for their wintering grounds. All the moths you see in the air are males — females are wingless and cannot fly. The females crawl up the trunk or branch of a tree and send out pheromones to attract winged males. After mating, the female lays eggs which hatch in the spring, and the larvae feed on a wide variety of deciduous leaves, favoring Trembling Aspens, Sugar Maples, American Beeches and willows. Periodic outbreaks of these caterpillars can result in heavy defoliation.

NB: “This is easily confused with Operophtera brumata – Winter Moth, which is an introduced species from Europe and an abundant pest in the Northeast. Also easily confused with Autumnal Moth (Epirrita autumnata).” Kent McFarland


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