I was volunteering in the gardens of the Stevens-Coolidge Place Wednesday morning when one of the staff members pulled several of us to a section of the garden housing a self-planted tomato plant. Usually we pull up or move plants that don't belong but somehow this tomato stayed, growing wild among the dahlias.
Matt grabbed us to share an interesting caterpillar. A tomato hornworm was perched on the plant, covered with tiny white oblong obtrusions. It turns out that these are cocoons of parasitic wasps.
This was my first introduction to a tomato hornworm.
The white obtrusions are actually the cocoons of a parasitic wasp. A female wasp has laid her eggs under the skin of that hornworm. As the eggs hatch the larvae actually feed on the hornworm insides. The larvae eat their way out of the caterpillar and spin the cocoons you see. Eventually adult wasps will emerge from the cocoons and the weakened hornworm will die.
The catepillar is quite large and apparently very destructive.