If imitation is the sincerest form of flattery, red-spotted purples live in praise of pipe vine swallowtails.  

Both creatures are butterflies but the swallowtail has the useful trait of toxicity, being poisonous to predators. And because red-spotted purples don’t have this attribute, they use Batesian mimicry to compensate.  

Batesian mimicry describes the copycat trait of one creature emulating another to gain an advantage that it doesn’t have. The term was coined by English naturalist Henry Walker Bates, who is credited with penning the first scientific account of this phenomenon.    

Mr. Bates studied insects in the Amazon in the nineteenth century and brought back almost fifteen thousand specimens from his years-long trip. He sent them back to England on three separate ships, to avoid the fate of his partner explorer whose entire collection burned up in a fire on the single ship that he had employed to transfer it.  

Look to the tails to differentiate red-spotted purples from swallowtails. Swallowtails have striking (namesake) appendages that extend beyond their main wings, which red spotted purples lack. Both species are large-ish black butterflies and the two might be confused by some.  

Red-spotted purples (limenitis arthemis), also called red-spotted admirals, are on the wing but will not generally be seen flitting among the flowers to sip their nectar. While they do partake in those petalled pretties occasionally, these butterflies are more likely to be consuming plant sap, fermenting fruit, dung, or even foraging in mud puddles.  

In Massachusetts, we have two generations a year. Sexes are mainly identical in appearance, with the female being just slightly larger.  Their eggs are a very interesting aggregation of hexagonal structures with spikes emerging from each. One at a time is laid on a variety of plants, including aspen, poplar, wild cherry, willow and birch. These eggs will hatch a caterpillar that will eventually metamorphose into the adult butterfly.  

Mimicry also comes into play for the red-spotted purple caterpillar, which is a muted multicolored blob that is a dead ringer for bird droppings. Yes, emulating poop is a survival method for this caterpillar and it does a great imitation.  

The caterpillar is also noted for its own droppings, called frass, which it will use to build a bridge of sorts on the midrib of a leaf that it is eating. After consuming the leaf from the tip back toward the stem, the red-spotted purple caterpillar leaves behind a line of frass, known as a frass spar, to deter predators from eating it. Any unsuspecting bird might see the caterpillar and want to go in for a bite, changing its mind when it realizes that it will get a mouthful of frass instead of the juicy caterpillar.   

The late-season caterpillars will go through a few instars before settling in for the winter. They will encase themselves in a rolled-up leaf secured with silk to wait out the winter. The caterpillar slows its breathing and metabolic rate, its fluids thin, and the percentage of water in its body goes from eighty to fifty to avoid damage from freezing.  

This master of mimicry will then emerge the next year, ready for a full life of impersonation and improvisation.

Suzan Bellincampi is islands director for Felix Neck Wildlife Sanctuary in Edgartown and the Nantucket Wildlife Sanctuaries. She is also the author of Martha’s Vineyard: A Field Guide to Island Nature and The Nature of Martha’s Vineyard.