Our most recognizable butterfly, the monarch, returns from wintering grounds as early as May and even into the summer. July, meanwhile, is a prime time to see them around the cottage or in your backyard.
Monarchs breed at almost any time of year, but it’s only in the summer that it happens here in the north. Mating takes at least 16 hours, usually after a male and female pair have performed an aerial, circling courtship ritual. Why does the main event itself take so long? Once a pair is attached at the abdomen, males gradually form a gelatinous capsule filled with sperm and protein. It’s time-consuming—this life-giving capsule equals five to 10 per cent of the male’s body weight. The female needs both sperm and protein to produce offspring. Adults, unlike plant-eating caterpillars, don’t get any protein in their diets. (Butterflies only eat flower nectar.)
Every day, for several days, females lay 20 to 80 green eggs—each about the size of a pinhead—on the undersides of milkweed leaves. Milkweed is the monarch larvae’s only food source. Once the babies hatch, they eat non stop for up to two weeks, growing larger and shedding their skin five times. Eventually, the black, yellow, and white caterpillars are 2,700 to 3,000 times their hatching weight. No wonder the Very Hungry Caterpillar was so hungry.
Milkweed is a monarch’s dietary staple in part because it contains toxic sap. This doesn’t harm the monarchs, but, since they store it in their bodies, it does make the caterpillars and butterflies taste nasty to birds or other predators.Caterpillars pupate for up to 15 days, then emerge as butterflies—ta da!—and live for two to six weeks. It’s the season’s fourth generation of butterflies, which bust out between August and September, that migrates back to Mexico for the winter.