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Sunlight, Sodium, & Spiders: The Life Of A Montana Butterfly

Spring azure butterfly.
Elena Gaillard (CC-BY-2)
Spring azure butterfly.

A cluster of male butterflies called "blues" are sipping minerals from a damp, sandy patch at river’s edge. Each of the nickel-sized insects probes the sand grains with a proboscis, a tongue of sorts that’s more like a drinking straw. Then, something strange interrupts the peaceful scene. A butterfly keels over. I peer more closely and see a slender, brown spider guarding its prey. I am puzzled, until I study the surroundings. Then I realize that similar spiders ring the entire flock, each hiding in ambush behind the pebbles. The moment a butterfly ventures too close to the edge of the sand, a spider leaps out. It happens so fast, I can never see the actual tackle, only the tattered, frail wings. The drama continues for half an hour, until a cloud obscuring the sun sends the hapless butterflies whirling off to safer grounds.

Like revelers at a bachelor’s party, many kinds of male butterflies seek this social gathering on mud or wet sand. Normally, there is safety in numbers. When one butterfly lands without becoming the victim of a frog or bug or spider, the rest flutter in beside him. In this case, only those blues crowded into the group’s center were safe. It seems to be a chance worth taking. The pursuit of sodium ions and possibly nitrogen and amino acids may be important to help them in the strenuous task of mating.

One of our early spring butterflies, and widespread across North America, the common blue or spring azure butterfly inhabits Montana’s mountain canyons and valleys with year-round water.

During their brief adult life, little more than a week, the lilac-blue-tinted males patrol for partners. That means almost constant flying in search of the subtle females, a paler blue with some white and brown on their hind wings.

To find the right species and gender, males rely on movement, color and sometimes the scent of a female butterfly. During that time, it’s not just spiders that try to pounce upon them. Dragonflies, wasps, beetles, lizards, frogs and even mice and birds may snack on a blue.

The slug-like caterpillars that will metamorphose into the delicate flyers would appear to be a more substantial feast for a predator, yet surprisingly this stage of a blue’s life proves less perilous. The larvae while away their days munching flowers. Their sweet diet helps them to secrete a honeydew. Ants, like beekeepers, tend the caterpillars and harvest the honeydew. When, for instance, a spider crawls too close to their caterpillar, the ants swarm upon the would-be attacker.

In Montana, we have 186 recorded species of butterflies flitting everywhere from backyard window boxes to the top of Granite Peak. The good news for butterfly novices is that, unlike birds, our butterflies fall into just a few families: swallowtails, sulphurs, brush-footed, gossamer wings and skippers. I’d suggest starting with a copy of the pocket-sized "Golden Guide to Butterflies and Moths". Then, plan on time in sunshine, among flowers and beside patches of damp earth.

Vladimir Nabakov wrote often about butterflies, including these words: "From the age of seven, everything I felt in connection with a rectangle of framed sunlight was dominated by a single passion. If my first glance of the morning was for the sun, my first thought was for the butterflies it would engender."

"Field Notes" is produced by the Montana Natural History Center.

(Broadcast: "Field Notes," 7/19/15. Listen weekly on the radio, Sundays at 12:55 p.m., Tuesdays at 4:54 p.m. or Fridays at 4:54 p.m., or via podcast.)