Aug 23, 2007

Doomed Hornworm

Janice, of Rosalita-demon-dog fame, has encountered yet another unholy beast. She found this tomato hornworm (lepidoptera sphingidae) on her tomatoes in New Jersey, US. I've encountered these critters before, and they are huge - up to 4"! And the moth they become is truly monstrous - my cat won't even touch them. The caterpillars wreak havoc on tomato plants.

But some of you more astute pest experts or entomologists may see this photo and cry, "Nay! That cannot be a tomato hornworm, despite that horn on its head. Look at those white rice-looking things on its side!" Aha, but we have you. Janice has more to relate: those white protuberances are pupae.

What? Pupae? But the caterpillar hasn't...what? See, those are the pupae of a small parasitic braconid wasp (cotesia congregatus). The eggs have already hatched, the larvae have eaten away at the insides of the hornworm, and then formed these pupae. When the new wasplings emerge the caterpillar will be killed, and the new wasps will seek out still other hornworms in which to lay their eggs. See? Even wasps can be a useful means of pest control.

Isn't that a cheery tale?

Thanks for the photo and the info, Janice.


14 comments:

Anonymous said...

Ugh. I actually feel sorry for the caterpillar. That is a horrible way to die!

Leslie said...

Man, that helps put high school in perspective, huh?

Anonymous said...

Thank you for that scroll down. I think if the picture had just been unleashed on me without having time to prepare for what I was about to see I might have been a little sick. That is one of the illest things I've seen in a second.

meg said...

bug eggs...parasites...my two biggest fears...it's horrible!

pkeli said...

AARRGGG!! The poor caterpillar. What a way to go!! And speaking of bad ways to go, tomato hornworms always remind me of a Fear Factor episode where the contestants had to eat a number of tomato hornworms alive and they were BIG and very juicy. I wonder if any of the hornworms had some of these parasites on them that no one noticed at the time....

Anonymous said...

That is totally gross! I think I've lost my appetite for the week. yech!

bats said...

Rock on, wasps!!!
(Not that I want to actually see this in real life, but we did do the tomato-growing thing for a number of years, and damn those hornworms!)

Arachnophile said...
This comment has been removed by the author.
Arachnophile said...

Warning, GEEK RANT AHEAD:

DUDE! I'm sorry but parasitic wasps are pretty cool too. If you ever read "Parasite Rex" you'll learn how the larvae sometimes make the caterpillar’s lifespan much longer than normal by making it crave more food and delay reproduction!

Uhm... On that note, it those are symptoms, then I'm not sure that I'm not infected myself...

One of my most formative experiences as an undergrad was when, on a trip for field school, I cut open a goldenrod gall expecting a certain kind of caterpillar or beetle larvae (can’t remember). What I found was a nearly-adult wasp that was quickly collected by our entomologist. He explained that this wasp mom inserts her LONG ovipositor into an already formed plant-gall so that her young could feast on the trapped larvae, thus replacing it altogether.

Ingenious, if not compassionate. ;)

Seriously though, Darwin himself had a hard time dealing with the nasty needs of the parasitic wasp. Look up his letters to Asa Grey the American Botanist (an unabashed evangelical) who was one of Darwin's most loyal friends for their discussions about how much these beasties bothered Darwin.

GEEK RANT OVER!!! ;) :p

Nebulous Grey said...

AWESOME.

Anonymous said...

Makes you wonder if a hornworm could have some innate capacity for considering suicide... I mean, doomed is doomed, and frankly getting eaten from the inside out by parasitic ANYthing is just not worth the extended lifespan.

Life is just a bowl of...parasitic wasp larvae. Bleagh.

Anonymous said...

When i looked in the mirror this morning after being outside, I saw this same creature on my shirt (near my neck!) i was a little creeped out then, but even moreso when i went out to delicately remove it with a small twig and it deflated like a balloon. What, but i was so gentle!! Anyway, google "catapillar white rice-looking" and found your article here. Very interesting but very gross in my opinion.

(i went back out and burned them all to save future caterpillars from this horrible fate)

Anonymous said...

Quote:
"...despite that horn on its head."

The horn is NOT exactly on this poor guy's head. Yep, that's the other end! Moth caterpillars do have a tendency to grow the horns in their rear ends... I wonder why!

Arachnophile said...

Whow! Anonymous... #2? That's quite the story. It must have been almost eaten out if it just deflaited like that! What an experience!

Y'know, they are starting to think that humans may have some parasite that effect our behavior. Isn't THAT fun to think about. ;)