Tuesday, February 14, 2012

Love is in the Air

(Valentine's Day edition...)

Let's imagine that you're a young, fertile female, and your biological clock is quickly winding down. It's a great big world out there, and you need to find a mate ASAP. What he looks like isn't a high priority, which is fortunate because it's not safe for either of you to go looking for love in broad daylight. Your only hope is that he somehow finds you at night, in the dark.

What's a girl to do? She must deploy her secret weapon -- pheromones.

Hemlock Looper moth on a cottonwood leaf (c) John Ashley
Hemlock Looper moth on a cottonwood leaf (c) John Ashley
Welcome to the secret sex lives of moths. Moths use airborne chemical scents -- or pheromones -- to locate, identify and choose their mates in the dark. Moth pheromones are often species-specific, which helps to prevent pairings with similar-looking but unrelated species. Females and males both rely on this chemical courtship, but in slightly different ways.

Female moths have special pheromone-producing glands that are located in two of their abdominal segments. "Calling" occurs after sunset and peaks sometime before midnight, as the virgin females release their magical come-hither perfumes into the wind. They must sit tight while calling and hope that a male arrives. Females of some moth species (but no males) have even traded in the ability to fly in order to produce more eggs -- they couldn't go looking for a male even if they wanted to.

Moth antennae (c) John AshleyMale moths tend to have larger, feathery antennae, with each one harboring upwards of 17,000 microscopic pheromone sensors. Males fly upwind into the pheromone gradient, searching for the virgin female from as far away as three miles. When a male arrives, the female won't accept him by sight (it's dark), only by his chemical cue. So he releases his own male pheromones at close range, and this confirms his identity to the female. Male moth pheromones also change composition slightly as they grow older. And the females, in turn, show a preference for choosing an older male to mate with.

Moth antennae (c) John AshleyMoth mating can last for many hours. Afterwards, the fertilized female stops calling at night and begins looking for places to lay her eggs. Males continue to "sniff" with their antennae, just in case another mating opportunity appears on the wind.

Moths first appeared about 600 million years ago -- long after flowering plants -- as one of the last insect groups to evolve. Now we call them "Lepidoptera," or the "scaly-wing" order of insects. That's because moth wings are covered with thousands of tiny scales that aid in flight and show subtle colors.

Of roughly 150,000 Lepidoptera species that have been identified so far, more than 130,000 are moths, and the vast majority of these are nocturnal. That leaves us with a subset of almost 20,000 Lepidoptera species that fly during the daytime and are often brightly patterned and colored. These are the butterflies -- easily the most popular insects in the world. In Montana, there are currently 322 confirmed moth species and 212 confirmed butterfly species, with many more waiting to be discovered.

Satyr Angelwing butterfly showing clubbed antennae (c) John Ashley
Satyr Angelwing butterfly showing clubbed antennae.
Diurnal butterflies probably branched off from the nocturnal moths to fill a different niche, feeding on nectar-producing flowers that are open during the day. Like their moth cousins, butterflies still use pheromones for mating. But because they are active during daylight, most of the butterfly species have also evolved brightly-colored and boldly-patterned wings. Perhaps due to these addition of visual cues for mating, butterflies have smaller, simpler, clubbed antennae -- not the elaborate, feathery antennae of most moths.

Maybe now it's easier to understand why there are so many dull-colored, similar-looking moth species (they're mostly night fliers, use mostly chemical cues for mating), and why the butterflies tend to be more colorful and easier to find (they're mostly day fliers, use mostly visual cues for mating).

From this perspective, maybe we can start showing moths the kind of love that we lavish upon butterflies. After all, butterflies are just fancy moths.

Butterfly and Moth Teacher's Guide (K-12)
National Moth Week, July 23-29, 2012
Butterflies and Moths of North America
The Moths of Canada
The Lepidopterist Society