Exploitation of environmental noise by an araneophagic assassin bug

Predatory arthropods that specialize in invading webs and preying on the resident spiders (‘araneophagic predators’) face special challenges. As webs are exceedingly good at transmitting vibrations, it is difficult for a web invader to move through the web and remain undetected by the spider. An araneophagic predator that generates vibrations in the web may risk prey escaping or even counterattacking. To increase the chances of an undetected approach, predators may exploit episodes of environmental noise to approach, while their prey’s ability to detect them is compromised (‘opportunistic smokescreen behaviour’). Here we provide the first experimental evidence of convergent opportunistic smokescreen behaviour in an araneophagic insect, Stenolemus bituberus Stål (Reduviidae), which preys on web-building spiders. We tested how two common types of environmental noise, wind and localized vibrations in the web, influence the predatory behaviour and success of assassin bugs when hunting spiders. We found that assassin bugs were more likely to catch the spider in the presence of wind. During episodes of environmental noise, assassin bugs stepped more often and walked in a more continuous manner, apparently exploiting the opportunity to approach while the prey’s sensory system is less able to detect the predator. Changes in predatory behaviour in the presence of environmental noise were not evident when S. bituberus was in an unoccupied spider web. This supports our hypothesis that noise-related timing of behaviour reflects decisions made as part of a predatory strategy, rather than responses to physical disturbance.