Cave fights for food: Voracious spiders vs. assassin bugs

Killing and eating of potential competitors, also known as intraguild predation, is a rare event that occurs only in specific situations such as severe scarcity of food resources, resulting in the competition between predators.

A recent paper in the open-access journal Subterranean Biology examines the case of a wandering spider species (Enoploctenus cyclotorax) seen to prey upon assassin bugs (Zelurus diasi) in a limestone cave in Brazil.

Even though such type of ecological interaction is uncommon, it is potentially important since it may decrease the competition between apex predators and thus, affect their population dynamics. Zelurus and Enoploctenus are voracious predators with a wide distribution in caves and epigean environment. Both of them have similar diets. In normal conditions, spiders reject assassin bugs as potential prey, so intraguild predation cases occur only in very specific situations.

From the perspective of the participants, intraguild predation is a dangerous strategy because the prey is also a predator, armed and capable of killing. However, in caves, this could be a very useful behaviour since food resources are scarce and have low density.

"This may be an important factor, maintaining the species in that challenging environment," concludes lead author of the study Dr. Leopoldo Ferreira de Oliveira Bernardi.

The scientists suggest that probably prey scarcity has left little choice for spiders, and that's why they ended up feeding on an unconventional type of prey in their diet.