In the annals of beedom, much is said of the ubiquitous honeybee and mighty bumblebee, but few have heard of the Herculean labors of Hylaeus sp.— a diminutive creature just 7 millimeters long and weighing a scant 0.01 grams that is credited, at least by one biologist, with saving Christmas. For the Hylaeus bee has come to the aid of a rare New Zealand mistletoe, Peraxilla tetrapetala, which can live a century, producing spectacular red buds each December.
Peraxilla flowers cannot open themselves and are normally pried open by birds—two honeyeater species, tui and bellbirds, being the chief pollinators. As the flowers are rather large, it takes considerable force to open them. Birds twist the tip of the petals- -a task compared to opening a childproof cap—to secure a nectar reward and, as a byproduct, pollinate the flower. Pollen, which explodes from the flower upon opening, coats the birds, thereby catching a ride to other ripe blooms.
This venerable arrangement, which yields brilliant scarlet displays in time for Christmas, is in jeopardy from two fronts: The mistletoe is being eaten by opposums recently brought to the country for their coveted fur. Meanwhile, the honeybirds are under attack by other nonnative species, including rats, cats, and ferrets. As a result, seed production from Peraxilla has declined.
That's where tiny Hylaeus has stepped in. Biting and clawing for all they're the worth, the bees manage to open about one in four mistletoe buds. It takes them roughly 100 times longer to get the job done than tui honeybirds, but that's understandable considering the bees weigh one-ten-thousandth as much as the honeybird. The bees are not nearly as efficient at pollen transfer as the honeybirds, partly because they're so small they can miss the flower's stigma altogether. Nevertheless, a team of ecologists from the U.S. and New Zealand have found that when honeybirds are absent, Hylaeus doubles the number of seeds ripened per flower.
"This is an extreme case of ecological replacement of vertebrates by an invertebrate," the researchers conclude. Pound for pound, they consider Hylaeus bees potent pollen harvesters and valued allies on the conservation front.
More than 80 percent of the world's 250,000 flowering plants depend on animal pollinators, and roughly 15 to 30 percent of the food eaten throughout the world comes from plants pollinated by these creatures.