Issue Date: March 12, 2018
For arthropod escape artists, survival depends on size
Beetles’ explosive exit strategy
Shinji Sugiura caught his crawly contenders at night. Long after tourists left the forest trails in central Japan, the Kobe University biologist collected bombardier beetles, along with their natural predators, the sticky-tongued toads, to see which bugs were best suited for survival.
Bombardier beetles are a resilient bunch. Armed with a chemical weapon that helps them escape their attackers even from within the toads’ tummies, the beetles blast a hot spray of water vapor and irritating compounds called quinones that makes the toads vomit them out. The beetles’ defense system, while explosive, isn’t surefire. Sugiura and colleagues set out to find out why through a series of experiments in which toads and beetles were placed inside small enclosures where they duked it out one-on-one (Biol. Lett. 2018, DOI: 10.1098/rsbl.2017.0647).
First, the team tried placing toads with beetles that were unable to release chemicals: The scientists got the beetles to prerelease their spray by tugging on their legs so that once they were swallowed, they would be chemically defenseless against the toads. None of these beetles made it out alive, confirming that the spray was indeed their ticket to freedom.
Next, they moved on to fully armed beetles ready to battle. The toads swallowed these beetles, tongues lashing out for precision strikes, in every case. In 43% of the experiments, the toads threw them up, anywhere from 12 minutes to almost two hours later. The beetles’ exoskeletons may help them survive the toads’ digestive juices, though the mechanism is unclear.
Ultimately, the researchers found that the deciding factor in who would win between the toad and beetle was size. Larger beetles were more likely to survive than smaller beetles, and larger toads had a better chance at keeping down their lunches. The toads, unharmed except for possibly some upset stomachs, were returned to the wild. The scientists kept the surviving beetles. Most lived at least two weeks, and some survived up to 18 months, post puke.
Roaches’ gravity-defying getaways
Meanwhile, across the Pacific Ocean on the campus of the University of California, Berkeley, scientists were hunting for another insect known for its escape prowess: the American cockroach. Though for Kaushik Jayaram, who has studied roaches for almost a decade, they’re fairly easy to catch: “You can just go sneak up behind them and grab them.”
One escape tactic that Jayaram, now a Harvard postdoc, and colleagues hoped to harness for robotic design was the roaches’ ability to go from the ground to walls. The team expected to see some fancy footwork. Instead, they watched in amazement as high-speed cameras revealed roaches managed the maneuver by charging into walls with utter abandon (J. R. Soc., Interface 2018, DOI: 10.1098/rsif.2017.0664).
The researchers proposed that the roaches owe their ability to make this 90° move to their small size and hardy exoskeleton, calculating that critters under 1 kg can rely on brute mechanical force to flip themselves from floor to wall. Using this principle, the team designed a small, 16-g robot that successfully replicates the roaches’ vertical maneuver. Jayaram says he’s still intrigued by the cockroaches’ abilities but would prefer to see them flex their skills in the lab, and not in his home.
Tien Nguyen wrote this week’s column. Please send comments and suggestions to email@example.com.
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