Monday, July 29, 2013

Eight-spotted Forester Caterpillars

Roy Thompson sent us these pictures of caterpillars.  Here he shows what a walk in the woods by a sharp-eyed and curious naturalist with a modern phone camera can accomplish. 

He is one of several of our Butterfly House friends who can't pass a chewed leaf without pausing to see what's eating it.  In this case he was working when he saw a tree draped with grapevine and inspected the leaves.  He found several eight-spotted forester moth caterpillars, Alypia octomaculata,  of varying ages and used his I-phone to get their pictures.  After that he carefully collected the caterpillars and the grapevine leaves to raise them in a safer predator-free environment.

Early instar out for lunch
After emerging from their tiny eggs, these caterpillars likely chew up the remains of their former home before eating through the nearest leaf.  From this time on they will be non-stop eating machines.  Most lepidoptera (butterflies and moths) caterpillars require specific food plants to survive and grow.  In the case of these foresters, they need grapevine or Virginia creeper.  They eat everything tender enough to chew including small tendrils, leaving only the heaviest veins and leaf petioles.

They will be going through five ever larger caterpillar stages, called instars.  An early instar is seen to the right crawling up the petiole of a leaf.  They eat constantly, pausing only to avoid bad weather and to occasionally slip into something more comfortable.

More accurately, they slip out of something uncomfortable, skins now too tight to hold their expanding bodies.  This shedding or molting starts by attaching the rear of their abdomen to a structure, then unzipping the skin on the back of the head before crawling out of the old skin like we crawl out of a sleeping bag.  The new skin has room to expand, containing its host until it is ready to progress to the next instar stage.

Fourth instar- Click to enlarge
Like many other caterpillars, each instar looks a little different in color or pattern.  Some types of caterpillars change color and shape so dramatically that you would never even guess that they are the same species.  In this case the last instars look similar although larger.  Soon the last instar, seen at the top, will form a pupa, the last step before the final reincarnation-like act of emerging as a beautiful moth.

Life is hard if you are a juicy colorful caterpillar perched on a leaf.  Grape growers consider them a pest and may spray them.  These cats defend themselves from predators by vomiting a clear orange fluid.  They also will drop off the leaf and are spared a rough landing by a bungee-like cord of silk.  Roy's cats are living in a more protected environment so you and I will have to wait a while for the next installment in their story.

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