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  • Randall Benton / Sacramento Bee

    A Pipevine Swallowtail Butterfly flies among blue plumbago at the Arboretum at UC Davis.

  • Randy Pench / Sacramento Bee

    A pipevine swallowtail butterfly caterpillar feeds on Dutchman’s pipevine, its only source of food, at the Effie Yeaw Nature Center.

Garden Detective: Mystery caterpillar could be swallowtail butterfly

Published: Saturday, Sep. 28, 2013 - 12:00 am

We have recently been inundated by a strange, dark green, small caterpillar; it looks almost black. These caterpillars range in size from a half inch to three-fourths of an inch in length.

We first noticed them in mid-September as they appear on our cement walks around 5 p.m. We believe they are eating newly planted grass. And they squash a very pretty dark green!

This is the first time we have seen this varmint. What is it and how do we eradicate it? We are testing soapy water now to control it.

Mike Collins, Lodi

According to UC master gardener Veronica Simpson, it is difficult to identify the caterpillar from the pictures you supplied. We at the Master Gardener office have narrowed it down to (at least we believe) a pipevine swallowtail butterfly caterpillar of the Papilionidae family.

The pipevine swallowtail is a beautiful butterfly. Its wings are glossy blue-green with orange spots on the undersides of the hind wings.

These butterflies are seen in Northern California where Aristolochia californica grows. Commonly called Dutchman’s pipevine, this is a deciduous vine with 1-inch, purple-striped, pipe-shaped flowers. The pipevine is the food plant of the butterfly’s larvae. The larvae is the only stage that chews plants.

The caterpillars are satiny deep brown or black with brilliant orange spots. The pupal stage is in the winter and is a light green or brown chrysalis anchored in some protected spot on the vine. If you see this caterpillar, there likely is a pipevine in the neighborhood.

Butterflies add beauty and are considered a welcome addition to the garden. Some adult butterflies are beneficial pollinators for plants and flowers and help to attract other beneficial insects to the garden.

If you find it necessary to control the caterpillar population, natural enemies – such as native wasps and many birds – are a means of control without pesticides. Removing the round rust-red colored eggs that are laid on the pipevine is another means of control.

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