It has glamorous color, seduction and desire, competition and urgent need. And the stakes are life-and-death. Pollination is nature’s great drama. Without it, life as we know it would end.
But it’s often hidden – it takes close attention to see the interplay between plants and their pollinators. Biologist Peter Scott paid that attention to ocotillos in Big Bend National Park. He found an unexpected bond between the plants and an industrious desert creature – the carpenter bee.
“Ultimately I spent about 10 years, in parts of various springs, going to different parts of the range and just sitting down and watching for hours at a time,” Scott said. “You'd be watching enough plants and flowers that you'd feel like you had a chance of estimating the visit rate generally in the population.”
Now an Indiana State University emeritus professor, Scott did PhD research in Big Bend in the 80s. He planned to study hummingbird breeding. That meant studying ocotillos. Plants with red, tubular flowers, like ocotillos, are often hummingbird-pollinated. Scott assumed ocotillos were a main food source for hummers here.
He’d park a stool 20 feet from a stand of ocotillos, and watch. A few hummers came, as did other birds – verdins, Scott’s orioles. But the dominant visitors were Xylocopa californica – carpenter bees. They’re among the largest desert bees, with bodies an inch long.
Carpenter bees are known to “rob” nectar, using specialized mouthparts to pierce flowers for the sweet stuff, without moving pollen at all. That’s not what was happening here. The bees were cutting ocotillo flowers for nectar, but females were also covering themselves in pollen. It’s a messy business.
“And as opposed to honeybees and bumblebees,” Scott said, “which are usually quite finicky about packaging up their pollen and wetting it down, carpenter bees are more like, ‘Cover me up, and I'll carry it back and worry about that later.’”
Carpenter bees are so named because they dig into wood, to create long tunnels within as nests. They can be a menace to homes. But in wild places, they’re picky about nesting locales. In the desert, it’s the stalks of agaves, lechuguillas and sotols.
Females amass pollen and nectar in their nests, lay an egg, create a sawdust partition, and repeat. Each larva, when it hatches, has its own chunk of nutritious “bee bread.”
It wasn’t easy, but Scott located and extracted samples from 16 nests. Then, colleagues analyzed the contents of the bee bread. There was creosote and mesquite pollen. But more than half was ocotillo. The bees depend on ocotillos to feed their young in spring.
Scott watched bees as they covered miles of desert, among ocotillos and their nests. He determined they were highly effective pollinators for the iconic plants.
Scott also studied ocotillos in the Sonoran Desert; hummingbirds are important pollinators there. But in Big Bend, carpenter bees and ocotillos clearly rely on each other. It’s what scientists call a “mutualism.”
“In this case, we could make the case that each organism was contributing to the other's reproductive success,” Scott said. “So in that case, even though we don't know quantitatively how important each is for the other, necessarily, you can see that there's an effect, a potential effect on population size.”
An ocotillo can create half a million flowers in its life. Perhaps only one will reach maturity. But ocotillos don’t flower in vain. For us, they bring color and beauty to even the driest spring. And as Scott’s research shows, they help sustain the web of desert life.
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