Where Do the Butterflies Go? Winter Survival Tactics of Local Lepidoptera

What a wild fall and winter we had in late 2024 and early 2025! Moths and butterflies held on longer than I can ever remember, with nighttime lows only dipping into the 40s for most of November and December. It was downright weird to see Monarch butterflies even hanging on into November, and at night, walking around with my headlamp, it wasn’t uncommon to find a number of moths out and about when I would have expected them to be absent. But winter did finally arrive in Cape May, and just like that, nary a butterfly or moth could be found.

This got me wondering, where do they go? And what do they do to make it through to the following year? Well, it probably wouldn’t surprise you to find out that they all don’t do the same thing. If you’ve spent any time in Cape May during the fall, you’re familiar with the Monarch butterfly, our most mobile of migrant butterflies regularly stopping over here. The Monarch, like many songbirds, heads south to overwinter in the mountains of northern Mexico, an amazing feat by any organismal standard, but given that it goes through several generations from when it emerges from its winter roost in the spring, until the migratory generation that will make the long journey to Mexico is born in the fall, I think it gets the award for most extreme lifecycle. While Monarchs head south, though, a myriad of other species of butterflies have their own fascinating winter strategies.

Over 114 species of butterfly have been recorded in the state of New Jersey and nearly that number in Cape May alone, each of which can be classified as either a resident, immigrant, or vagrant. Examples of immigrant species would be those that come up from the southern climes each year, like the Common Buckeye, Painted Lady, and Red Admiral. We can expect some to many of these butterflies each summer, and any that are around once winter sets in will likely die, replaced again in subsequent summers by a fresh crop from the south. Vagrants are similar to immigrants, but they are much rarer and may constitute one or a few individuals. The bulk of the species, though, are resident, meaning that they overwinter as an egg, caterpillar, chrysalis, or adult. It’s truly mind-boggling to think of a tiny butterfly egg surviving months of freezing cold temperatures!

A great local example of an overwintering wonder is the Mourning Cloak butterfly. As winter sets in, the adult of this species enters a state of diapause, a slowing down of the metabolism so that it can overwinter tucked into crevices in tree bark, or in leaf litter, and emerging in the first warm days of spring (although they can emerge as early as January in South Jersey!). You can often tell a Mourning Cloak that Has overwintered because their wings are rattier than a freshly emerged one. Each early spring sighting excites me; it is a testament to their tenacity against winter’s harshness. Of course they do have some very important protection, in the form of anti-freeze pumping through their tiny bodies. Glycerol, stored in their bodily fluids, prevents the formation of ice crystals, which allow every stage, from egg or larvae to chrysalis and adult, to withstand freezing temperatures in ways that are almost unbelievable.

Our state butterfly, the Black Swallowtail, is an example of one that overwinters in the chrysalis, or pupa, stage. Prior to winter the caterpillar finds an appropriate location to form its chrysalis, which is strategically camouflaged in brown hues to match the background of fall and winter leaves. Glycerol provides protection against freezing, and diapause gives the butterfly all the time it needs until it’s ready to emerge as a fresh adult as early as mid-March in our neck of the woods. Cape May numbers peak in May, and these majestic butterflies can be found as late as the end of November. So, the next time you spot a Mourning Cloak on a sunny January day, or a fresh Black Swallowtail in spring, take a moment to marvel at their remarkable strategies for survival. Even in Cape May’s coldest months, nature finds a way to thrive.