Invertebrates
Eastern Tiger Swallowtail
Papilio glaucus · also called swallowtail butterfly
An eastern tiger swallowtail caterpillar begins life looking convincingly like a bird dropping, grows into a later stage sporting false snake eyes on its thorax, and finally emerges as a tiger-striped adult whose wing tails may exist purely to fool a bird’s aim. Three disguises, one life cycle.
Overview
The eastern tiger swallowtail, Papilio glaucus, is a widespread butterfly native to forests and open habitat across eastern North America. Its layered sequence of caterpillar camouflage strategies and adult wing decoys make it one of the more elaborately defended butterflies in its range.
A different disguise for every stage
Rather than relying on a single defense, the eastern tiger swallowtail changes strategy at each stage of its life, moving from bird-dropping camouflage to a snake-mimicking bluff before finally trading both for tiger stripes and decoy tails as an adult.
Status
Least Concern — widespread and stable across suitable forest and open habitat throughout eastern North America.
Eastern Tiger Swallowtail: common questions
Why does an eastern tiger swallowtail have tails on its wings?
An eastern tiger swallowtail's distinctive tail-like hindwing extensions may act as a decoy, redirecting a bird's strike toward a less vital part of the wing rather than the butterfly's actual head and body, potentially allowing the butterfly to survive an attack by sacrificing only a piece of wing.
Why do young eastern tiger swallowtail caterpillars look like bird droppings?
Young eastern tiger swallowtail caterpillars closely resemble bird droppings in both colour and shape, an effective early-stage camouflage strategy that helps them avoid detection by predators during the vulnerable period before they grow large enough to rely on other defenses.
Why do some eastern tiger swallowtail caterpillars have fake eyes?
As an eastern tiger swallowtail caterpillar grows past its bird-dropping-mimicking stage, it develops large false eyespots on its thorax that resemble a small snake's head, a startling visual bluff intended to deter birds and other potential predators from attacking.
Why do some female eastern tiger swallowtails look completely different?
Female eastern tiger swallowtails can occur in two distinct colour forms, one resembling the typical yellow and black tiger-striped pattern and another almost entirely dark, with the darker form believed to mimic the toxic, unpalatable pipevine swallowtail as protection from predators that have learned to avoid it.