Parsnip Webworm Moths
Many people are familiar with the invasive Wild Parsnip’s (Pastinaca sativa) ability to cause a chemical burn on human skin when the skin is exposed to sunlight. The compound that causes the burning and blistering (furanocoumarin) is in the plant’s sap, and thus is present in the leaves, stems, flowers and fruits of Wild Parsnip.
What is lesser known is that there is a non-native moth (Parsnip Webworm Moth, Depressaria radiella) that was introduced to the U.S. in the 1850’s whose larvae feed on Wild Parsnip. As a result of this herbivory Wild Parsnip upped its chemical arsenal and started producing more concentrated furanocoumarin.
What humans avoid, Parsnip Webworm Moth larvae take advantage of. Most of the plant toxin these larvae ingest is excreted in their feces. Some, however, is incorporated into the caterpillar’s silk webbing which encases the flowers and seeds that they eat, serving to protect the larvae from predators.
The adult Parsnip Webworm Moth is about half an inch long and is brown with black flecks.
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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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Eastern Black Swallowtails Laying Eggs
Eastern Black Swallowtail (Papilio polyxenes) butterflies are mating and laying eggs. The female Eastern Black Swallowtail can appear quite frantic as she visits multiple host plants just long enough to leave a very tiny, spherical, pale yellow egg before heading on to the next plant. In the wild, Queen Anne’s Lace, Wild Parsnip, Golden Alexander and Poison Hemlock are favorite host plants; in vegetable gardens you frequently find larvae (if you should miss the eggs) on dill, fennel and parsley. Entomologists have found that host plant odor is one of the cues involved in the Eastern Black Swallowtail’s choice of where to lay eggs.
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