HABITAT: Monarch caterpillars need milkweeds as host plants ... Caterpillars take 9 to 14 days to go through five instar stages before pupating. The first instar larva, just out of the egg, is solid ...

And that allowed the caterpillars to hold the toxins in their bodies, helping to fend off predators. More information: Anja Betz et al, Late-instar monarch caterpillars sabotage milkweed to ...