Friday, October 21, 2011


We've been out enjoying the gorgeous fall weather lately, with lots of walks around a nearby park. We keep coming across caterpillars that are making their way to a safe place to pupate for the winter. Naturally, my boys have to carefully move them off of the path and out of harm's way. There are enough squished ones, already.

Many of the caterpillars are covered in stiff hairs. They practically sprint across the path. But another is slow, confused, trying to dig a hole.  It has a smooth, velvety-looking body. No hair. But each and everyone of this kind has something else.

Not the best photo, I'm afraid.

See those little white things behind the head? Know what they are? They're wasp eggs. This caterpillar was parasitized by a parasitoid wasp. What, you ask, is that? A wasp laid its eggs on the caterpillar. When the eggs hatch, the wasp larvae will consume the caterpillar, eventually killing it.

The crazy thing is, the wasp eggs seem to have changed the caterpillar's behavior. Every other caterpillar was headed for high ground to spend the winter. All of the parasitized ones were trying to dig into the rocky path. Very un-caterpillar-like behavior.

Wasps often dig burrows where they stash a caterpillar with eggs on it. Parasitoid wasps don't disable their kids' future meal; they let the larvae take care of that. But something about the eggs must mess with the caterpillar's brain, changing its behavior in a way that will help the wasps, not the caterpillar.

It's been zombified.

Are there other zombies in nature? You bet. Entomogenous fungi do it, too. When the fungus takes up residence inside an insect's body, it eventually consumes the body tissues. In the process, it alters the insect's behavior.

All that white stuff is the fungus. (source)
The zombified critter climbs up to an exposed perch. Not the best place for an insect (too easy to spot by things that want to eat it), but the perfect place for the fungus, which releases spores on the wind.

Even rabies zombifies animals by putting them in attack mode. What better way to spread to new hosts than by hiding out in saliva and driving the current host into a frenzied, froth-mouthed state of attack?

Watch out for zombies this Halloween. You never know where they might turn up.

What is your favorite spooky critter?


  1. Think my most spooky creature is a large moth!

  2. That is just creepy. I think every bug in Austrailia goes on that list because they all seem to be poisonous.

  3. Never trust parasites, they usually want something for nothing.

    Interesting post, especially the part about altering the creature's behaviour. Never liked anything parasitic, but they do tie in with zombies and blood drinkers.

    Spooky critter? The Pine Beetle (eater of forests).

  4. Very fascinating. Have you played the computer game Plants vs. Zombies? Too much fun! I don't think I have a favorite spooky critter. Favorite insect? Maybe honeybees and fireflies.

  5. Carole Anne: After watching Silence of the Lambs, I was terrified of moths for years!!

    Matt: Yep. Scary, isn't it? ;)

    Alex: Good thing those parasites don't affect humans, isn't it? ;)

    DG: Incredible how small insects can destroy entire forests.

    Christie: I haven't. I try to avoid computer games; once I start playing, I can't seem to stop!