Although the male Gluphisia septentrionis moth is only 1.5 centimeters long, it can eject water 0.25 meters or farther. Flash photography shows the individual droplets that make up each of the 4,325 water ejections that Cornell biologists counted while one moth drank continuously for more than three hours.
By Roger Segelken
While human barflies order another round because the pretzels are so salty, a tiny moth is drinking prodigious quantities of water just to get the sodium it craves.
Careful measurements by Cornell chemical ecologists Scott R. Smedley and Tho mas Eisner, as reported in the cover article of the Dec. 15 issue of the journal Science, demonstrate what lepidopterists have long suspected but never proved: Adult moths' and butterflies' "puddling" -- as sipping from mud puddles and other sources of moisture is called -- is all about salt.
Sodium acquisition may be the primary function of puddling, said the ecolo gists, who work with a creature that could be the world's champion drinker. They watched in the field as a male Gluphisia septentrionis drank and voided continuously for nearly three and a half hours, consuming more than 600 times its body mass: 38.4 milliliters of puddle water.
"I weigh 165 pounds," said Smedley, a postdoctoral associate in the Cornell In stitute for Research in Chemical Ecology (CIRCE), comparing himself to the 1.5 -centimeter-long moth. "To keep up with Gluphisia , I'd have to drink 12,000 gallons at a gallon per second."
The male Gluphisia moth, which lives
less than a week as an adult, doesn't want the salt just for himself, observed Eisner, the Schurman Professor of Biology. Rather, the male is preparing to mate and pass along the concentrated sodium -- as a kind of nutrient legacy -- in his sperm packet, Smedley reported in his 1993 Ph.D. thesis.
In a separate article, set for publication in Proceedings of the National Academy of Science, Smedley and Eisner will tell what happens next: The short-lived female doesn't keep the donated sodium entirely to herself, either, "but bestows it in large measure on the eggs, thereby endowing the offspring with a first dose
of the valuable ion," they wrote in the Science article.
Life is not easy for the Gluphisia moth, which lives throughout much of North America. Its favorite food, while in the larval stage, is poplar (or quaking aspen) leaves. Poplar could be on the menu for salt-restricted humans because, as trees go, it's a particularly poor source of sodium. Fortunately for Gluphisia caterpillars, their parents bequeath a gift of salt, a head start in a life that will end soon after they do the same for the next generation.
When they analyzed male Gluphisias' bodies after their drinking
bouts, the scientists found sodium concentrated in the reproductive parts. "The female, potentially as deficient as the male in sodium, because her larval diet is the same as the male's, receives supplemental sodium from the male at mating, with the sperm package," Smedley and Eisner wrote in Science.
The male's sperm package is transferred to the female in a five-hour-long copulation. Then the female allots much of the male-donated nutrient to the eggs.
"It's like dad giving the kids a one-a-day vitamin plus minerals," Smedley said, "to get them going in life."