Wednesday, August 31, 2011

Zombie Worms From Planet Sphinx

This time of year, when you're harvesting tomatoes, you often notice part of the plant where the leaves seem to be missing and all that's left are stubby stems.  This is not a deformed tomato plant.  Look closely and you will see a stem that seems to be especially thick and stubby like so: 

Tobacco Horn Worm (Source)
The gigantic worm above is a tobacco horn worm.  It is a positively ravenous caterpillar that literally stuffs itself with tomato or tobacco leaves.  If you touch one, it seems to be so full that its skin feels like a grape leaf around a dolma.  It eats so much of the tomato plant that it can reduce tomato productivity dramatically.  Farmers dislike these caterpillars, but I bet most of them also admire the strangeness of these creatures. 

Tobacco horn worms grow from tiny eggs deposited on tomato plants by the Carolina sphinx moth, a gorgeous night creature that moves and hovers like a hummingbird.  It has a coiled proboscis that it uses to probe nectar from night-blooming flowers trumpet-shaped flowers.  Here is a sphinx moth feeding on an azalea:

Sphinx moth feeding.  (Source)
 Sometimes when you see a tobacco horn worm, it will appear to be covered with dozens of white, ovoid bead-like objects.  When you see this, you know the horn worm is one of the walking dead.  The white things are the pupal cases of a type of braconid wasp, which lays its eggs under the skin of the horn worm.  The eggs hatch inside the horn worm and eat the worm from the inside out.  The larvae begin to burst out of their horn worm and weave little white cases with lids around themselves.  In a few days, they will emerge as adult wasps, and the horn worm will expire as a shrunken husk of itself.  The adult wasps will go on to infect and kill other horn worms.  Braconid wasps are friends of the farmer because they help do the work of dispensing with horn worms.  Anytime a farmer sees an infected horn worm, she lets it be so that more wasps will hatch.  Farmers can even order braconid wasps in the mail to release on their farms.  Here is an infected horn worm:

I know it's hard to see, but there is a parasitised tobacco horn worm in the middle of the picture.  I'll bring a better camera to work tomorrow.
 Here are some better pictures I didn't take from this website:

A good picture of an infected hornworm.

An adult braconid wasp spreading its wings for the first time.

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