Active volcanoes don't usually seem like valuable real estate. If the looming risk of eruption isn't scary enough, there's the intense heat, sloshing lava and acidic gases, all rising from a murky moonscape that offers few, if any, signs of life.
Ecosystems can emerge in surprising places, though, if a few brave pioneers lay the foundation. And at one caldera in Nicaragua, scientists have discovered an amazing new example: hundreds of bees living on the lip of an active volcano, getting almost all their food from a single wildflower species adapted to volcanic acid rain.
The bees are Anthophora squammulosa, a solitary, ground-nesting species native to North and Central America. Led by ecologist Hilary Erenler from the University of Northampton in the U.K., the study's authors found the bees nesting "within meters of an active volcanic crater," they write in the journal Pan-Pacific Entomologist. Female bees dig tunnels into volcanic ash to lay their eggs — a habitat so inhospitable the study describes the insects as extremophiles.
"The nest location is exposed to continuous, strongly acidic gas emissions," according to Erenler and her co-authors, "and sporadic vent-clearing episodes that blanket the surrounding area with ash and tephra."
The volcano is Masaya, a 635-meter (2,083-foot) shield volcano known for frequent eruptions. Researchers found the bees nesting in volcanic ash by a crater named Santiago, which is "one of the world's strongest sources of sulfur dioxide" (SO2), they note in their study about the discovery. These gas plumes are highly acidic, they add, "creating a clearly defined 'kill zone' under which vegetation is either entirely suppressed or partly damaged, depending on proximity to the source."
Masaya volcano is highly active, with about 20 eruptions recorded over the past century. (Photo: Jorge Mejía Peralta/Flickr)
SO2 is known to cause a variety of problems for bees, they add, such as reduced foraging activity, slower development of larvae, lower survival of pupae and less longevity in adults. Around the Masaya bee nests, SO2 levels were detected ranging from 0.79 to 2.73 parts per million (ppm), but previous studies have shown damage to bees from SO2 levels as low as 0.28 ppm. The researchers don't know how A. squammulosa can live in this environment, where SO2 levels peak at 10 times that level, noting more research will be needed to reveal the bees' survival secrets.
What do they eat?
Since the bees live in Masaya's "kill zone," the researchers wanted to find out where they get nectar. They searched for any flowers within 725 meters (2,378 feet) of the nest area, trying to mimic the distance traveled by a foraging bee. They also looked for bees returning to their nests, capturing 10 and swabbing pollen from their legs.
The flower search turned up 14 plant species, although the captured bees told a different story: Of all the pollen in those 10 samples, more than 99 percent came from a single wildflower species, Melanthera nivea. This hardy member of the daisy family ranges from the Southeastern U.S. to South America, and past research has revealed adaptations that help it tolerate volcanic acid rain.
The bees seem to rely almost entirely on Melanthera nivea, also known as snow squarestem. (Photo: Dick Culbert/Flickr)
Why do they live there?
A. squammulosa wasn't known to nest in volcanic ash until now, nor was any species in its genus. In fact, the behavior has only been reported in a few other bees, and there's a key difference, the authors say. Previous reports of ash-nesting bees came from exposed roadsides in Guatemala, about 6 kilometers (3.7 miles) from the nearest volcanic vent. This population of A. squammulosa, on the other hand, nests just meters away from a gas-spewing crater in a volcanic kill zone.
Of course, this habitat poses "several distinct challenges," the researchers write. They cite high SO2 levels as the main danger, but also note insects can be hurt by volcanic ash itself. A 1975 study of ash eruptions in Costa Rica showed that abrasive ash wore down insects' exoskeletons, while ingesting ash-contaminated pollen and nectar caused physical and chemical damage. An eruption could also wipe out the Masaya bees, either directly or by killing the plants that seem to be their only food source.
But living by an active volcano has perks, too. Ground-nesting bees avoid nesting near plants with fast-growing roots, which can break up their underground tunnels, and seem to like habitats with sparse vegetation. "The warm open area on a relatively gentle slope with a distinct lack of vegetation and a loose substrate may provide ideal nesting conditions," the authors suggest. And while a few predators do prey on the bees, "their density and activity may also be impaired by the high levels of gas."
The Masaya bees still have a dangerous lifestyle, but protection from natural predators would be a big advantage. And if volcanic gases can do that, maybe they offer other benefits, too? Bees may not live on Masaya to escape humans, but given the growing dangers we pose to bees around the world — via habitat loss, insecticide use and invasive species — they're lucky to live anywhere that scares us.