Complex sentence: The caterpillars are black or green, they have narrow lighter stripes that are on the back and sides, they spit a out a brownish substance, and they spring into the air and wriggle a lot when they are disturbed.
Split into simpler sentences: The caterpillars are black or green, with narrow lighter stripes on the back and sides. They spit a out a brownish substance, spring into the air and wriggle a lot when they are disturbed.