Yes Chilly, there are about 10,000 things (a modest estimate) that eat larva. In addition to the above i would add wasps that chow down on caterpillars and/or inject them with parasites. Wasps are the primary predators of caterpillars in my garden and they range in size from 2" to almost microscopic. Also caterpillars can have parasites from birth passed down from the mother butterfly or picked up from the host plant or immediate environment. If caterpillars are bothered by predators on the host plant, they may wander away from time to time. Also, they will occasionally leave the host plant to molt, especially if bothered by various predators on their host. The caterpillars are especially vulnerable during molting. Take a look at your plants from time to time to discover what kinds of bugs are regularly hanging around and/or also populating the plants and you may get an idea of what is happening to the caterpillars.
