The caterpillar shown above is dead. Although the wasp larva, while growing inside the caterpillar, appears to spare the muscles and nervous system of the caterpillar so that the caterpillar will be able to hold onto the twig or leaf and also retain its reflex to move its head away from contact with another caterpillar, the caterpillar usually becomes entirely unresponsive within a few hours after the wasp larva emerges.

Below is a picture taken through the low-power lens (described in tools) of 2 wasps and the cocoons from which they hatched. That's a standard-sized paperclip next to them, so you can see that they are very small. Not the sort of wasp that we worry about encountering.

Notice the wonderfully long antennae!

Point-of-view is important in deciding our alliance with one creature or another...for a rather different perspective on caterpillars and the wasps that parasitize them, have a look here: http://homeharvest.com/beneinscaterpillars.htm

Also do a Google "Images" search (first click on the "Images" tab and then enter the search terms) on 'caterpillar wasp' to find out lots more about parasitoid wasps. For example, this is an excellent page about these wasps (and much else about butterflies): http://www.learnaboutbutterflies.com/Enemies%20of%20Butterflies.htm 

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