50 Nebraskaland • October 2024
THE LAST STOP
Nature isn't always for the faint of heart, but it is
consistently fascinating. For example, take the gruesome
scene I found playing out on the siding of my garage last
fall. A green caterpillar was thrashing about while numerous
larvae were crawling out of its body. The scene was being
observed by several small wasps.
Fortunately, with the help of friends — especially Dr.
Enakshi Ghosh of Colorado State University — I can explain
the scene to you. The caterpillar was a larva of a cabbage
white butterfl y, an invasive species from Europe. The
emerging larvae were the off spring of a European parasitoid
wasp introduced to North America to help suppress
populations of the butterfl y. Adults of that wasp species
fi nd caterpillars by following the scent plants release as a
response to the caterpillar's feeding activity. When a wasp
fi nds a caterpillar, she inserts her ovipositor (a skinny tube
eggs feed through) into it and lays up to 30 eggs inside the
hapless creature.
Just to punch up the story a little, the wasp also introduces
a virus into the caterpillar that takes over its brain and keeps
it alive and moving, even as its innards are consumed by the
wasp's kids. That turns the caterpillar into a kind of guardian
for the larvae inside it by repelling "hyperparasitoids," which
are wasps that try to lay eggs on the larvae of parasitoid
wasps. I know, right?
Anyway, what I was seeing was wasp larvae exiting the
caterpillar and immediately spinning yellow fuzzy cocoons,
inside which they'd pupate and become adults. The larvae
were probably the babies of the initial parasitoid wasp, but
they might also have been the young of a second wasp that
laid eggs on the larvae of the fi rst. It's all very complicated.
Oh, and those small wasps hanging around while all this
happened were yet another species of hyperparasitoids.
They were waiting to lay eggs on the wasp cocoons as soon
as they were created. As a result, when I checked back a few
weeks later and found empty cocoons, I didn't know what
species had emerged from them. It might have been a wasp
that laid eggs on the caterpillar, a wasp that laid eggs on
those eggs, or a wasp that laid eggs in the cocoons of either
of those others. Happy Halloween.
This looks like a lot. There's even more happening than you might guess. CHRIS HELZER
By Chris Helzer
GARAGE CARNAGE
