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These Silk-Swinging Caterpillars Will Ruin Your Picnic

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California oak moth caterpillars eat all the leaves on an oak, leaving a brown skeleton. Then they rappel down on a strand of silk, twirling and swinging. If you were enjoying the shade, good luck getting out of their way. For the oak, the caterpillars are a bigger deal – will the tree survive?


Ahh. Time for a spring nap under this peaceful oak … unless that oak is under siege by clouds of amorous moths.

Unlike most moths, which are nocturnal, these California oak moths take over in daylight.

This female frantically beats her wings to spread her scent.

A male picks up the signal with his feathered antennae.


Every few years, the moths seem to appear out of nowhere and get down to business.

Once they lay their eggs, the oak is in trouble.

By summer, oak moth caterpillars cover its leaves. And they’re ravenous.

That bulbous head has powerful mouthparts that chew through the tough oak leaves.

The caterpillars eat and eat. They outgrow their skin six times.

They stuff themselves in the daytime, when birds and other predators can spot them easily. Their bright colors may signal a gnarly taste that keeps enemies away.

The caterpillars leave something behind: tough poop pellets called frass … a little fertilizer that will eventually fall to the ground. At least these gluttons give something back.

When they’re done eating, in a month or two, what’s left of the tree is a brown skeleton.

With full bellies, the caterpillars rappel down from the branches on long silky strands.

Sometimes they swing on their silk, Tarzan like, to get that laaast bite.

And down they go.

If you’re sitting below, you might just be in their way.

The caterpillar’s goal is to quickly attach to a hard surface and turn into a pupa.

In this moment of stillness, these destroyers become vulnerable to predators.

A wasp pierces the pupa to inject its own egg inside.

The wasp larva will feed on the developing moth … because in nature, one day you’re the diner and the next, you’re the meal.

And the oak? It’s tougher than it looks. It almost always survives.

In a month or two it grows new leaves. And if it’s lucky, these pernicious guests will stay away … at least for a few years.

Nothing, and I mean nothing, is better than a good parasite story. Am I right? Deep Look’s got you. Watch our episode on how mosquitoes use six different needles to suck your blood. And learn about a killer fungus that turns flies into zombies. You can thank me later.

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