The Status of Our Four-Winged Migrants

Jul 25, 2018


Coral Hairstreak on Milkweed
Credit Mark Faherty

It’s late July, which means it’s peak time for some of my favorite flying critters. They include many of our most beautiful species and one of our most impressive long-distance migrants. They can often be found gracefully winging their way through your yard on their four wings. That’s right – four wings – because it’s time to talk butterflies.


July is when the North American Butterfly Association organizes the so-called “Fourth of July” butterfly counts to keep tabs on populations of butterflies all over the continent. The counts are patterned after National Audubon’s Christmas Bird Counts in that “citizen scientists” head into the field on a specific date to tally all species and individuals within a 15-mile circle. Butterflies face the same threats as birds in the form of habitat destruction and the effects of climate change, so long-term monitoring is key to detecting problems.


I oversee the Truro count on which we can find over 30 species in a good year, though numbers were way down this year. The same goes for the Brewster Count, which includes Harwich, Eastham, and South Wellfleet, and was held this past weekend. In most years I would normally see at least 25 or 30 species on count day, but this year we had a measly 19 species, a 40% drop from last year. It’s not clear why, but there are reports of super low numbers and species diversity from the Mid-Atlantic States this year as well. Monarch numbers were average to above average at most sites, and many have been enjoying seeing them around after several years of scarcity.


To complete their life cycle, many butterflies depend on specific food plants for their caterpillars. The most familiar example is the Monarch, a comparatively huge and highly recognizable butterfly that only lays its eggs on various species of milkweed. But for many butterflies, the relationships are more complicated than just needing a type of plant. The Edward’s Hairstreak is a small, beautiful butterfly whose caterpillars eat Scrub Oak, a very common shrubby tree on the Cape and Islands. But in addition to patches of the host plant and some nectar sources for the adults, this species also requires a certain species of ant to be present. The ants, it turns out, protect the caterpillars from the many predators that would otherwise eat them in exchange for a “honeydew” secretion the caterpillars provide them. The caterpillars actually hide in the ant colony during the day and come out at night to feed. This relationship, from the butterfly’s point of view, is known as “myrmecophily”, which literally means “ant love”.


If you want to see butterflies in your yard, there are some plants you can include in your gardens or encourage around the edges and wilder sections. Great native plant choices to attract nectar-seeking insects include Swamp and Butterfly Milkweeds, Anise Hyssop, Echinacea, Bee Balm, and Sweet Pepperbush. Tried and true garden standards like salvias and catmints are not native, but they aren’t invasive and can be even more attractive to nectar-hungry bees and butterflies than the native species. But providing host plants for the caterpillars is more important than flower nectar, so encourage or plant local species like cherries and oaks, Little Bluestem and other native bunch grasses, blueberry, and a ton of herbaceous species you might just think of as weeds. 


Everyone knows Monarchs, but it’s time that you got to know some of the less noticeable but way more common species in our area, like the tiny and stunning American Copper and the lovely Pearl Crescent, which resembles a tiny Monarch. Check flowering Butterfly Weed plants for the handsome Coral Hairstreak, which uses Beach Plum and other shrubs as larval host plants, and which are very tolerant of close up photography.


Learning these species is your homework for this week. And if anyone manages to work “myrmecophily” into a conversation, or better yet a Scrabble game, please let me know – you’ll get extra credit.