Friday, April 23, 2010

Tent Caterpillars

When we see a web like this in the crotch of a tree, we attack it with a stick to destroy the nest before the caterpillars strip the leaves from the tree.  After learning about the Eastern Tent Caterpillar's family life, I will always think twice (and then usually go ahead with the attack.)
Life started for this tent from the mass of eggs which were tightly glued to a small stem on this small wild plum tree.  Tent caterpillar host trees are in the Prunus (cherry, plum, peach, apricot, almond) and Malus (apple) family.  Eggs over winter in this hard wad and the larvae chew their way out as the trees bud out in the spring.
Since it was in a grove of multiple small plum trees near the house, I decided to watch the caterpillars develop.  The web was only two inches long at the start and there was no apparent activity.   The web grew daily as the leaves of the plum diminished.  There were now signs of caterpillars crawling over the web surface most of the day.

The Eastern Tent Caterpillar is the most social of the Missouri caterpillars.  Typically they move out to feed three times a day- before dawn, mid-afternoon and after sunset.  They leave a pheromone trail between the feeding site and the tent. When a caterpillar discovers a particularly good site, it leaves a stronger trail, sometimes recruiting the whole colony.
Although they would appear to be sitting ducks for predators, they have their defenses.  When attacked by a parasitic insect attempting to lay its eggs on a caterpillar, it starts thrashing about, followed rapidly by the whole colony, creating a confusing target.  Caterpillars feeding on cherry leaves acquire cyanide from them which they can regurgitate on predators.  Needless to say, few birds (except for the cuckoo) acquire a taste for them.
Perhaps the most amazing thing about them is their construction skills.  They daily crawl over the tent surface, laying down silk as they go.  As the silk dries, it shortens and pulls away from the underlying layer, creating a space.  A large tent is made up of multiple concentric layers which they can enter.  They are able to control their temperature this way.  A colony huddled together in the center of the web during a freeze emits metabolic heat and can maintain a temperature of 70-80 F.
The last of the six instars leaves its siblings to develop a cocoon on the ground.  The moth that emerges is ordinary.  Its only claim to fame is a faint resemblance to a gypsy moth.
Most of the trees which are denuded of leaves will leaf out again in a few weeks with no permanent harm.  For that reason, I could easily let all of them alone to complete my life cycle, except for one thing.  My wife will still rip down their tent with her accustomed violence.
Another view of the life of a different species of caterpillar is in this utterly fascinating 5 minute Video  of the life of a caterpillar which is parasitized by multiple wasp larvae.  Fantastic footage, so don't miss it, but don't watch it during dinner.
A good source of information is at the Henderson State site.
Trivia:  Ingestion of these caterpillars by horses can cause 
Mare Reproductive Loss Syndrome'

1 comment:

  1. We thought these were bagworms! Ha - what a surprise!