Even cockroaches hug each other. It may not be the most romantic image in the world, but romance matters little when you need to survive: cuddling these insects is a strategy to avoid wasting fundamental resources – specifically water.
This is what a study published in the magazine explains Ethologywhich tells the story of the cute tactics of a species of African cockroach, the Madagascar whistling cockroach.
The cockroach most loved by entomophiles. Endemic to Madagascar, as its name suggests, the whistling cockroach is a large cockroach that can exceed 7 cm in length: its considerable size, and the fact that it “whistles” to defend itself from predators, have made it one of the insects most loved by entomophiles, who often keep them as pet exotic. Anyone who has ever raised one knows that the whistling cockroach hates light and cold, and above all prefers damp to dry weather.
Risk of dehydration. It is precisely this last detail that determines their social behavior. These cockroaches are insects that live in very large groups – but only at certain times of the year.
The climate of Madagascar includes a dry and a wet season, and it is the first that pushes the cockroaches to embrace each other. Like almost all insects, these cockroaches tend to lose water quickly: when the climate is too dry, they risk dehydrating very quickly.
The physics of cockroaches. The rate at which cockroaches evaporate body moisture is a matter of high surface-to-volume ratio – the same reason why larger animals lose heat more slowly than small ones.
To avoid dehydration, therefore, Madagascar whistling cockroaches “play” with this physical principle: by hugging themselves in large groups they increase their volume, reducing the rate of moisture loss. It’s a tactic already seen in action in other insects, particularly in the larval stage, but never before in one this large.
Seasonal sociality. Obviously, when the season is humid in Madagascar the situation is reversed: the cockroaches hug each other less and less often, they almost never gather in groups and when they do they limit the number of individuals that compose them.
This is because the collective hug is a decisive strategy, but with a dark side: a group of cockroaches is more vulnerable to predators than a solitary individual. This is why the sociality of whistling cockroaches is seasonal: if there is no reason to hug each other, it is better to keep your distance.
