Glossary

A cocoon is a protective casing spun from silk by moth caterpillars around the pupa as it undergoes metamorphosis into its adult form. The cocoon is an external structure, built by the caterpillar before it pupates, using silk produced by specialized glands.

A cocoon is not a chrysalis. A chrysalis is the pupal casing of a butterfly, formed directly from the caterpillar’s own hardened skin. Butterflies do not spin cocoons. Both structures shelter the pupa through metamorphosis, but they are produced differently and by different insects.

In the Santa Cruz Mountains, moth pupae overwinter inside silk cocoons in a range of locations depending on species:

• Suspended from twigs and branches
• Tucked within leaf litter
• Buried in loose soil
• Concealed inside hollow stems

Each placement reflects a survival strategy refined over millennia: camouflage, insulation, moisture regulation, and protection from predators.

Removing leaf litter, cutting back standing stems, or disturbing dormant soil in winter or early spring directly destroys cocoons before the adult moth can emerge.

One of the most striking examples in the San Lorenzo Valley is the Ceanothus Silkmoth (Hyalophora euryalus), a large native moth whose caterpillars feed on some of the valley’s most important native shrubs — including Ceanothus, manzanita (Arctostaphylos spp.), coffeeberry (Frangula californica), madrone (Arbutus menziesii), and native willows (Salix spp.) and alders (Alnus spp.) along riparian corridors.

In late summer, the moth caterpillar spins a dense, tough silk cocoon and attaches to a twig of its host plant, where the pupa overwinters until the adult moth emerges in late winter or early spring. Adults do not feed. Their sole purpose is to find a mate, and they live for only a few weeks.

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