2nd Brood of Black Swallowtails Emerging
The process of transforming from a caterpillar to a chrysalis is a miraculous one, but it’s especially intriguing when it comes to Black Swallowtails (Papilio polyxenes). For one thing, their chrysalises vary in color from green to brown, depending on the object on which they choose to attach themselves. Equally impressive, while it is still a caterpillar the Black Swallowtail spins a thread of silk from which it suspends itself. It uses this silk sling as support for the chrysalis that is revealed once the caterpillar splits and sheds its exoskeleton (see it dangling beneath the chrysalis).
The second brood of Black Swallowtails (Papilio polyxenes) is already emerging from their chrysalises this summer, mating and laying eggs during their two week adult life span. Look for the caterpillars dining on members of the Parsley family, including Queen Anne’s Lace, dill, parsley, fennel, celery and carrot foliage. (Photos from left to right: Black Swallowtail larva preparing to pupate, chrysalis (with cast off larval exoskeleton) and adult male Black Swallowtail)
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Black Swallowtail Larvae Defending Themselves
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.
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Black Swallowtails Laying Eggs
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.
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Wild Chervil Flowering
You can’t drive very far right now without seeing a sea of tiny, white flowers belonging to an invasive plant, Wild Chervil (Anthriscus sylvestris), crowding the shoulders of the road. A member of the carrot family, Wild Chervil leafs out early in the spring before most native plants and consequently shades them out and displaces them. It spreads aggressively and produces many seeds that are dispersed by birds, water and mowing (after the seeds have set).
Native to Europe, Wild Chervil was introduced in the early 1900’s to North America in wildflower seed mixes intended to reproduce the European countryside in gardens. Little did gardeners know that among these seeds was a plant that would outcompete native plant species and drastically reduce wildlife habitat. In addition to choking out native plants, Wild Chervil also is the host for a virus that infects carrots, parsnips, and celery.
Because it is a prolific seed-producer Wild Chervil can be challenging to eradicate. The best way to control it is to stop it from flowering and setting seed, but unless you mow early, every year, before its flower buds open, this isn’t a very effective method. Its up to six-foot-long taproot makes removing it by hand extremely difficult, but possible; however, this method also runs the risk of breaking off lateral buds at the top of its roots that can grow into new plants. Beware — Wild Chervil looks a lot like Poisonous Hemlock (Conium maculatum).
One of the few positive things to be said about Wild Chervil is that its flowers are a source of nectar for small bees, parasitic wasps, flies and beetles. Black Swallowtail larvae feed on the foliage. Many of these flowers are being visited now by thousands of flies in the Bibionidae family. Pull over the next time you see clouds of white smothering the edge of a road and look for these tiny, black flies. The males are the ones with the big eyes (pictured).
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