Butterfly Love

Spring is in the air here in Tucson, Arizona, and apparently the thoughts of butterflies are turning to love. I wrote the following for the Valentine’s Day issue of the volunteer newsletter at the Tucson Botanical Gardens, but cruising the grounds this past week I saw plenty of native butterflies in “action,” so to speak, like this pair of Giant Swallowtails outside our administration building.

Visitors to Butterfly Magic will never fail to notice when two butterflies are conjoined, and will ask you what is going on with that. Well, ok, so the butterflies themselves are not shy when it comes to courtship and sex. They have a limited amount of time to find acceptable mates and produce the next generation.

Among the more dazzling behaviors butterflies engage in is courtship. There are great differences in courtship behavior from family to family, and even species to species, but you can easily recognize certain postures and flight styles as romance-intended. Females may advertise their availability by perching with wings open and abdomen slightly raised. She may also “call” males by releasing a special chemical called a pheromone. Males detect the wind-wafted scent with their antennae and then quickly recognize her visually. Male giant silkmoths like the African Moon Moth and the Forbes Moth can home in on a female from up to a mile away (maybe even longer) by following her pheromone trail.

Male butterflies of many species have pheromones, too, designed to communicate individual fitness to a potential mate. Once he locates a female the male must convince her he is a worthy investment. He may do this by following her in flight until she lands, then hovering over her and showering her with his own “cologne” emitted from special scent patches on his wings, or from “hair pencils,” glands that he extrudes from the rear of his abdomen. Males of some Heliconiinae (longwings) go a step further and sprinkle an anti-aphrodisiac once mating has occurred. This discourages other males from usurping his genetic investment in that particular female’s offspring.

Should the female be disinterested in a suitor, she changes her posture, pointing her abdomen nearly straight up and essentially “mooning” the male.

The pursuit and hovering displays are characteristic of the male Priamus Birdwings and the Heliconius longwings. Morphos are less elegant. Males will land next to perched females and aggressively “nudge” them into compliance. Watch as a male bends his abdomen forward in an attempt to copulate.

Compatible males and females may eventually couple, tail-to-tail, facing in opposite directions. Males might even hang limply from the female as she remains perched. Occasionally the pair will even take flight, one of them carrying the other. Butterflies can remain coupled for as little as a few minutes to several hours. We had one pair of Priamus Birdwings (shown above) engaged for so long that the male actually perished while still connected to the female. While lengthy mating leaves both butterflies vulnerable to predation, it also prevents other males from mating with a given female, increasing the odds that the male will see some of his genes represented in the next generation produced by that female. Nature is full of such trade-offs.

Butterflies have the same sex organs as other animals, but they go by different names. The male penis is called an aedeagus (ee-dee-AY-gus). The shape and configuration of the aedeagus varies from species to species, largely preventing hybridization between different species. He also has claspers, the external genitalia that hold the couple together during sex. The female has a vagina (the “bursa copulatrix”), but also has a “receptaculum seminis” or “spermatheca,” a sac that stores sperm. Her eggs will not be fertilized until she lays them.

Whew! I managed to get through all that without even talking about contraception and the Butterfly Vatican.

A pair of Texan Crescents is shown above.