E-mail | SIS | Moodle | Helpdesk | Libraries | cuni.cz | CIS More

česky | english Log in


Animals are naturally trying to avoid becoming prey. Some depend on perfect camouflage, some prefer a hidden lifestyle, and some are equipped to defend themselves actively. However, even a wasp with a pointed stinger would rather fly away instead of fighting for its life. Could it somehow warn a potential predator ahead then? Aposematic signals have evolved for this exact reason. Aposematism is a easily-noticeable warning signal informing the recipient that the signaling animal is distasteful, venomous or otherwise dangerous. The striking yellow and black colors of wasps, newts or yellow-bellied toads are just that. Nevertheless, aposematic signals don’t end with coloration. Sometimes a smell is the best way to demonstrate how dangerous or distasteful one is. Whether a smell is truly a strong enough sign was investigated by a team of zoologists of the Faculty of Science, Charles University, led by Jan Raška.

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.

Left: Jumping spider Evarcha arcuata. Source - www.flickr.com, author Antonín Ťok.
Right: Firebug Pyrrhocoris apterus, a third‐instar larvae. Source – Wikimedia Commons, user Hectonichus

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.

Perception of olfactory aposematic signals by jumping spiders; Jan Raška, Pavel Štys, Alice Exnerová; Ethology; 2018

Iveta Štolhoferová

Published: Feb 18, 2019 06:50 AM

Document Actions