Wild Facts About The Spicebush Swallowtail Butterfly

Different Defenses For Different Ages

The Problem And Possible Solutions

• Butterfly caterpillars serve as food for a wide variety of predators, such as insectivorous birds, lizards, spiders, and predatory insects.
• Like all living creatures, butterfly caterpillars try to survive and have evolved various strategies to outwit would-be predators.
  • Some butterfly caterpillars defend themselves actively, such as with spines, irritating body hairs, or by being noxious or downright poisonous.
  • Other species defend themselves passively; they avoid notice by predators by mimicking inedible objects, like bird droppings.

Overachieving Caterpillars

• In contrast to many butterfly species who rely on only one or two defense strategies throughout their development, Spicebush Swallowtail caterpillars use different strategies as they age.

Nothing Edible To Eat Here

• Young Spicebush Swallowtail caterpillars avoid predation by pretending to be inedible by mimicking bird droppings.
• Their glistening, knobbly dark gray or dark green and white bodies look exactly like fresh bird droppings during their first three growth stages (called “instars”).
• To reinforce the illusion that they are bird droppings, young Spicebush Swallowtail caterpillars rest on the tops of leaves in plain sight.

Not Quite The Expected Tasty Tidbit

• Older Spicebush Swallowtail caterpillars molt into a snake mimic.
  • Their bodies turn bright green, and huge eyespots develop on their third thoracic segment.
    • Each eyespot is bright yellow with a large black “pupil” which looks remarkably like a snake’s face and eyes.
  • They also develop a tentacle-like structure called an “osmeterium”, that the caterpillars can evert and wave around.
• Once the caterpillars reach the snake mimic phase of their development, they change their behavior to maximize the effectiveness of this defense.
  • Instead of resting out in the open on top of leaves, they hide in little tents they create by bending leaves over and anchoring the edges with silk.
  • A predator peeking into a leaf tent expects to see a harmless and tasty caterpillar but is instead confronted by what appears to be an angry snake, complete with flailing tongue.
    • The element of surprise helps sell the illusion and, as few would-be caterpillar predators wish to tangle with angry snakes.

Would YOU Want To Eat Fresh Vomit?

• Looking like an angry snake isn’t the only trick Spicebush Swallowtail caterpillars evolved.
• They may also repel some predators by smelling really, really bad.
• The same osmeteriums that mimic snakes’ tongues are imbued with butyric acid, a noxious substance that smells like fresh vomit (Wagner 2005).