Wild Ideas: How butterflies mate  

During the few dry spells we’ve been having, especially warm, sunny ones, more butterflies have been showing up around my gardens. I’ve spotted several pairs mating, which is the sole purpose of the short adult phase of a butterfly’s life cycle. In most species, females have less than a week to find a mate, copulate, search for host plants and lay their eggs on them.

From a distance, a male butterfly finds a female by spotting ultraviolet patterns on the latter’s wings, but the males can get overeager, as the British website Learn About Butterflies explains: “During the initial ‘approach’ phase of mate location males will chase after almost any small moving object, including falling leaves, bees and butterflies of any species and either sex.”

The response of whatever the male is pursuing is key to the next phase in courtship, when pheromones come into play. These chemicals give butterflies two key pieces of information that determine whether they will proceed with mating: whether they differ in gender but of the same species. If what the male is pursuing fits those criteria, and the female is receptive, courtship begins. If a male discovers he’s pursuing another male of the same species, he usually battles his competitor for access to females. If the object of the male’s pursuit doesn’t fit into either scenario, the male continues his search for a mate.

For some species, according to Learn About Butterflies, exposing a female to male pheromones is all it takes for the pair to copulate immediately. Other species require a more complex courtship ritual that can include “a protracted series of visual, tactile or olfactory stimuli and responses” before copulation. For example, courting spicebush swallowtail couples fly slowly together for a while, the male above the female, according to “Butterflies of the East Coast: An observer’s guide,” by Rick Cech and Guy Tudor.

By Pam Owen
Two spicebush butterflies mate on meadow phlox

Lepidoptera genitals are among the most complex in the animal kingdom, with special claspers unique to each species that fit together like a lock (the female’s genitalia) and key (the male’s). This helps prevent two separate species from mating with each other, although hybridization, especially in closely related species, is known to occur.

During mating, the male butterfly, clasped to the female, inserts a spermatophore (sperm packet) into her ostium bursa (vaginal groove), a pouch at the end of her abdomen that is the terminal point of the tube through which she lays her eggs. As each egg passes down the tube during oviposition (egg laying), it is fertilized by the sperm. Butterflies often fly while hooked together this way, which Cech and Tudor refer to as “courtship flight,” but the term seems misleading, since the pair seem beyond courtship at that point. To see some amazing footage of butterflies competing, courting and mating, check out the “Sex, Lies and Butterflies” episode of the PBS series “Nature”.

Once the female is ready to lay her eggs, she looks for certain native plants that serve as hosts for the caterpillars that will hatch out. Some butterflies have several host species, others only one or a few. For example, spicebush swallowtails favor spicebush but also will lay their eggs on sassafras, both of which are in the Lauraceae (laurel) plant family. According to the Butterflies And Moths website, spicebush swallowtails may also use two other forest species in the laurel family, camphor and redbay, as well as tulip tree and sweetbay, in the magnolia family, and prickly ash, in the citrus family.

By Ryan Haggerty via Wikimedia
Spicebush caterpillars, with large spots resembling eyes, mimic snakes to scare off predators

The preferences of butterflies for native plants as hosts rather than nonnative is why planting native species is so important, especially since most native songbirds use butterfly and other larvae to feed their young.

Most eggs are laid separate from each other but often on the same host plant. After hatching, larvae eat and go through several stages of growth (instars). When ready, they make a cocoon (chrysalis), emerging from it as adults either during the breeding season or overwintering in this stage.

By Pam Owen
Great spangled fritillaries, like this mating pair, produce one extended brood from mid-May to late September

Depending on the species, butterflies can have several generations (broods) during the breeding season. Each brood flies looking for mates at the same time during the breeding season, so broods are also often referred to as “flights.” This terminology can get complicated, since more than one generation of the same species can be flying at one time. The handy “Northern Virginia Butterflies and Skippers: A Field Guide,” by Robert R. Blakney, lists the number and times of flights of our local butterflies.

Species vary in when they reach sexual maturity as adults. Some take only a few days, while others take longer. The adult monarch butterfly, known for its long fall migration to Mexico to spend the winter, delays its sexual maturity for nine months. The species breeds April through November, with the generation that emerges in August in the northern United States and Canada going into adult “diapause,” stopping maturation of their reproduction organs until after they overwinter. This enables them to instead put the energy they consume through nectaring into extending their life expectancy sufficiently to fly to Mexico, overwinter there, and fly north again in the spring to breed. Because of their longevity, this generation of monarchs is known as the “Methuselah generation.”

© 2018 Pam Owen

Pam Owen
About Pam Owen 324 Articles
Writer, editor, photographer, and passionate nature conservationist living in Rappahannock County, in the Blue Ridge Mountains of Virginia. Two favorite quotes: By E.O. Wilson, who coined the term "biodiversity," "Nature holds the key to our aesthetic, intellectual, cognitive and even spiritual satisfaction”; by Douglas Adams, “I love deadlines. I love the whooshing sound they make as they pass by.”