What Is the Big Yellow Butterfly With Black Stripes? Identifying the Eastern Tiger Swallowtail

Some butterflies you have to work to spot. The eastern tiger swallowtail is not one of them. It is big, bright, and slow enough to watch, gliding through backyards, parks, and woodland edges all summer and nectaring openly on flowers. Its size and its four bold black stripes make it one of the first butterflies most people in the eastern United States learn to recognize — right up until they meet the all-black version and get thrown completely.

How to Identify an Eastern Tiger Swallowtail

The classic yellow form is hard to mistake for anything else:

• Size: large, with a wingspan of roughly three to five and a half inches — one of the biggest butterflies you will see in an eastern yard
• Color and stripes: bright yellow wings crossed by four black "tiger" stripes on each forewing, with a broad black border along the wing edges
• Tails: a slender tail trails from each hindwing (the "swallowtail"), with blue scaling and a small orange spot near each tail
• Behavior: a strong, sailing flier that visits flowers in the open; males often gather at mud puddles and damp gravel to sip minerals, a habit called puddling

Males are always yellow. Females come in two forms, which is where the confusion starts: a yellow form that looks much like the male but with more blue on the hindwings, and a dark form that is almost entirely black. Even the black females usually keep a bit of blue on the hindwings and, in good light, show the ghost of the tiger stripes — a useful clue that a "black" swallowtail is really a dark tiger swallowtail.

Why Some Are Black Instead of Yellow

The dark-form female is not a different species — it is mimicry. She copies the pipevine swallowtail, a butterfly that is genuinely toxic to birds, borrowing that bad reputation for protection. The disguise is common enough in parts of the range, especially the South, that plenty of people never realize the big black butterfly and the big yellow one can be the same species. If you see blue-scaled hindwings and faint darker stripes on an otherwise black swallowtail, a dark-form tiger swallowtail is a strong bet.

The Caterpillar and Where They Live

Tiger swallowtail caterpillars feed high in the trees — on wild cherry, tulip tree, ash, birch, and willow — so you rarely stumble on them the way you do garden caterpillars. When you do, they are worth the find: a plump green caterpillar with two large fake eyespots behind the head that make it look startlingly like a small green snake. Younger caterpillars use the familiar brown-and-white bird-dropping disguise before turning green.

Because their host trees are so common, eastern tiger swallowtails turn up almost anywhere with trees and flowers across the eastern half of the continent, from deep woods to city gardens. They are completely harmless — they do not sting or bite, and the adults are simply after nectar.

Tiger Swallowtail Look-Alikes

A few other big swallowtails share the neighborhood, and a close look sorts them out:

• Canadian and two-tailed tiger swallowtails: very similar yellow-and-black relatives, separated mostly by range (farther north or west) and, in the two-tailed, by a second tail on each hindwing
• Giant swallowtail: even larger, but dark brown above with a diagonal band of yellow spots rather than a yellow background with black stripes
• Black-and-blue swallowtails: the pipevine, black, and spicebush swallowtails are the dark butterflies the dark-form female tiger swallowtail is imitating — telling them apart comes down to the exact pattern of spots on the hindwings

Not sure whether the big butterfly working your flowers is a tiger swallowtail, a giant swallowtail, or one of the dark mimics? Snap a photo and let Spotter identify it, and put a name to one of summer’s most reliable showstoppers.