Aptos, California (near Santa Cruz), has been undergoing an outbreak of oak moths (Phryganidia californica) since early this summer. This year's third generation of adults is now (2007-10-01) just emerging from the pupal stage.
Oak-moth caterpillars accumulate at the tops of fence posts, where they become torpid, and some small slugs — as many as seven, one evening — seemed to make regular evening visits to a fence post near my house. On closer observation, the slugs seemed to overlap the caterpillars more often than one would expect from chance, which suggested predation. This would be particularly interesting in view of the fact that birds seem uninterested in these caterpillars, and lizards react as if they tast bad [1].
The slug is believed to be Lehmannia valentiana.
Slug with caterpillars I offered. I don't think
the slug is eating these caterpillars. Unlike the
caterpillars in the rest of these photos, these caterpillars
had been plucked off the wall of the house and left in
a high-slug-traffic area.
Slug inspecting caterpillar on post.
Slug with caterpillar on birdbath pedestal.
I claim it's eating the caterpillar.
Slug with caterpillar on birdbath pedestal.
The slug has been distracted. Note that the right
posterior dorsal part of the caterpillar is missing.
Remains of the same caterpillar on the birdbath
pedestal. This photo was taken just 10 or 20 minutes after
the previous photo. I don't know why the slug left.
Remains of the same caterpillar, scraped off the
birdbath pedestal and photographed the next morning.
Note that much of the right posterior quarter, including
the right-hand prolegs, is missing.
Thanks to Janet Leonard for identifying the slug.
[1]: Anita Pearson, unpublished. If memory serves, the lizards in question were of the genus Anolis.
2007-10-01
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