The lava from the 2018 Kilauea eruption has cooled but still offers little to sustain plants or animals.
USGS/POLARIS/NEWSCOM
Last year, when the simmering Kilauea volcano had its most violent eruption in decades, massive molten rivers of lava slithered across a corner of the Big Island of Hawaii, swallowing up roads and parked cars, houses and meadows, even a boat marina. As the lava gradually cooled over the next few months, it left behind jet-black tendrils of lifeless, lumpy terra nova. For one tiny, unassuming Hawaiian native, however, all this destruction meant one thing: fresh real estate.
The lava cricket, Caconemobius fori—‘ūhini nēnē pele in Hawaiian—is, according to many biologists, the first multicellular life form to take up residence on new Hawaiian lava flows. How this poorly understood insect manages to thrive in a harsh, sterile landscape when virtually nothing else can is a mystery. This week, scientists are heading out to Kilauea’s latest lava fields in hopes of learning the cricket’s secrets. The answers may rewrite the rules on which adaptations make an animal a good pioneer.
Marlene Zuk, an entomologist at the University of Minnesota in St. Paul who is leading the first extensive study of these crickets in decades, concedes that they seem unimpressive next to the dramatic geology. “There’s the lava and the scape of this barren land, and then there’s this cricket.”
Hawaiian locals had long observed that in the wake of eruptions, ‘ūhini nēnē pele was quick to appear on the scene, but the species wasn’t formally described by scientists and given its Linnaean name until 1978. Four years earlier, a group led by entomologist Frank Howarth of Honolulu’s Bishop Museum was out exploring Kilauea’s lava fields when it spotted the crickets. Lacking formal traps, the group baited empty wine bottles with bits of “rancid raw cheese.” The improvised pitfalls snared 153 crickets over the course of 6 days.
Howarth and company learned the crickets show up on barren lava flows that had erupted as recently as 3 months earlier, before practically any other living thing. The insects eke out an austere existence by eating decaying plants that blow in with the wind and slurping sea foam, which contains a proteinaceous compound called albumen. By the time vegetation starts to grow, the crickets disappear. “If the plants have already moved in, it’s too late to find them,” Zuk says. No one knows where they live between eruptions.
The lava cricket sustains itself on sea foam and wind-blown plant remains.
ALAN CRESSLER/FLICKR
When Kilauea erupted last year, Zuk remembered Howarth’s work and realized it was the perfect opportunity to finally learn more about the enigmatic lava crickets. The National Science Foundation green-lighted her application for one of its rapid-response grants, designed to fund research triggered by sudden events such as hurricanes.
Zuk calls the lava crickets “unlikely colonists” because they lack the features biologists have come to expect from species that lead the charge into new environments. Rosemary Gillespie, an evolutionary ecologist at the University of California, Berkeley, explains that such animal front-runners are usually generalists, able to live almost anywhere. They tend to be highly mobile, able to fly or float over great distances. And they tend to breed easily and quickly.
None of this describes the lava cricket. It isn’t a generalist; it has been found only on young lava flows. It lacks wings and can’t fly. And without wings, it can’t sing, which raises another question: How do males find a mate?
When the crickets do mate, a gruesome habit presents a further challenge to survival. While copulating, the female sucks a bloodlike fluid called hemolin from the male’s leg, giving their potential progeny a nutritious leg-up. He can lose 3% to 8% of his body mass during the ordeal. “It’s extremely hot and dry [on recent lava fields] … so donating any kind of fluid is probably a pretty substantial cost for the males to bear,” says Justa Heinen-Kay, a postdoctoral entomologist in Zuk’s lab.
These conditions might even contribute to a rather rare evolutionary scenario, says Jeremy Marshall, a cricket researcher at Kansas State University in Manhattan. “Usually when we think about who is choosy, it’s females of a species,” he says. “But if mating is going to be even more costly for males, we might get a situation in which … we’d expect to see the opposite, for males to become the choosy ones driving sexual selection.”
When Zuk and Heinen-Kay visit Kilauea’s recent lava flows this week and later this summer, they will be armed with time-tested traps of wine bottles and raw cheese and some new questions. They’re hoping to find out, for instance, whether the insects possess some novel type of chemical signaling that allows them to follow and find each other in the lava cracks. They will also try to determine whether these crickets congregate in groups or are solo explorers. Finally, they would like to catch some pregnant females to start a colony back at their lab.
Whatever strategies these lava crickets are employing to become the initial colonizers of one of the most extreme environments on Earth are likely to surprise biologists, Zuk says. Either these crickets share some as-yet-unknown attributes of animals like cockroaches or our ideas about what make for a good early colonist are wrong, she says. “Either way, it’s going to be a really exciting insight into adaptation.”