Where will it jump? Using high-resolution, high-speed imaging of flies in action, the scientists are reporting today online in Current Biology, they found that if the descending swatter (they used a 6-inch-diameter black disk, dropping at a 50-degree angle toward a fly) comes from in front of the fly, the fly moves its middle legs forward and leans back, then raises and extends its legs to push off backward, away from the swatter. Are you approaching your quarry from behind? The fly has a nearly 360-degree field of view and can see behind itself, so when it spies the swatter behind it it moves its middle legs a tiny bit backward and flies forward. With a swatter from the side, the fly keeps its middle legs still and leans in the opposite direction before jumping. The idea is to position its center of mass so that when the legs push off the fly will evade the swatter.
“When the fly makes planning movements prior to takeoff, it takes into account its body position at the time it first sees the threat,” Dickinson says. “The fly somehow ‘knows’ whether it needs to make large or small postural changes to reach the correct preflight posture.” It does all this “long” (in fly time) before it takes off. “These movements are made very rapidly, within about 200 milliseconds” of seeing the swatter, says Dickinson, “but within that time the animal determines where the threat is coming from and activates an appropriate set of movements to position its legs and wings.”
Don’t believe the folk wisdom that if you approach the fly really, really slowly so your swatter doesn’t stir the air then the fly won’t notice. The Caltech scientists found that flies can tell you’re coming by sight alone—and remember that 360-degrees of vision thing.
It is Dickinson’s hope that discoveries about the fly’s neuronal processing will shed light on more complicated brains, not that his work will help humans kill flies better. His admiration for the little guys’ abilities, in fact, have made him hope that people will “think before they swat.”
Having recently tipped you off to the most effective way to swat a fly, Lab Notes is now proud to share the secret to killing a skittering, running-for-its-life cockroach. Thanks to research on animals’ predator-escape mechanisms (which we’re sure has relevance to deep mysteries about neural circuitry, or evolutionary biology, or something), it can now be revealed that the best way to smoosh a roach is to aim for a 90-degree angle from where the thing is currently headed (that is, figure it’ll make a sharp right or left turn) or a 180-degree angle (that it’ll reverse course).
Yes, you might need assistance to cover all three possibilities. A 3-to-1 ratio of humans to roaches is about the right show of force, given how the things have outsmarted and out-reproduced us for so long.
As scientists led by Paolo Domenici of Italy’s Istituto per l'Ambiente Marino Costiero report in Current Biology, cockroaches fleeing predators seem to choose an escape route at random. “By using one of a number of possible trajectories,” said Domenici, “cockroaches may behave with sufficient unpredictability to avoid the possibility that predators will learn their escape strategy. The predator is made to guess.” But roaches do not run in random directions. Instead, find the scientists, they select an escape route at only a few fixed angles from the threat: a 90 or 180 degree angle from the attack. “This is where squashing could be aimed,” Domenici said, “although we like cockroaches and would recommend no squashing.”