|Monarch Caterpillar- Wikimedia|
Many species of butterflies have caterpillars that can ingest toxic chemicals from their larval food plants without harm. These chemicals are incorporated into their bodies and remain in the adult butterflies. A predator that eats one and gets sick won't want to eat another one or anything that looks like it. Many of these butterfly species have distinct bright warning patterns, called aposematic coloration, which advertises their toxicity.
Some butterflies have evolved similar patterns even though they lack the toxicity, and are therefore avoided by predators. This is called Batesian mimicry. Examples include the viceroy butterfly which resembles the toxic monarch. The toxic pipevine swallowtail has several mimics including spicebush and black swallowtails. You can see these examples again when the Friends of the Garden Butterfly House opens this May at the Botanical Center.