Popular Science: I SENSE A FIREBUG NEARBY…
Larvae of the firebug (Pyrrhocoris apterus) were chosen for the experiment. The species conveniently combines two aposematic signals: bold red-and-black coloration and a very distinct scent produced by specialized repellent glands. Jumping spiders (Evarcha arcuata) were tested as predators. It is a common Czech species of spiders with big eyes searching for prey by sight while running in grass.
When a larva was attacked, it defended itself with a stinking secretion. This efficiently discouraged a jumping spider from other attacks and the larva was usually unharmed in the end. After several trials, jumping spiders learned not to attack firebugs in the first place. By what clues did they learn this, however? Could that have been based solely on the intense red and black colors of the firebugs? The next step was a two-choice test. Jumping spiders could choose to enter either an arm with a firebug scent or an arm with no additional scent. The majority of the jumping spiders did indeed choose the firebug scent-free arm. Interestingly, all the males chose the arm with no additional scent but not even half of the females made this choice. The smell of firebugs didn’t seem to repel jumping spider females. Generally, though, females were much less active than males, probably causing the imbalance in behavior.
Not only bold coloration but also the scent can indeed efficiently protect firebugs against their predators. However, almost nothing is known about which chemicals spiders react to. Further research is thus going to be devoted to determine the component of the firebugs’ secretion spiders are sensitive to.