Different caterpillars eat different things. Most caterpillars eat leaves and stuff and need to be sprayed with water. Monarch caterpillars eat milkweed plants and eat a lot of it! If you have any caterpillars they might eat leaves that you pick from your back yard! MAKE sure you spray them!
Woolly bear caterpillars are the larva of Isabella Tiger moths. They can eat lettuce if you feed it to them. Their very favorite food is clover, but they also like maple, aster, birch, sunflowers, and dandelions.
No, not all caterpillars with spikes are poisonous. Many of the caterpillars who have spikes are poisonous, but others use this as an advantage because if they seem to look poisonous then predators will not eat them.