Predatory flexibility of an araneophagic assassin bug derives from a few behavioural rules

The assassin bug Stenolemus giraffa preys upon various web-building spiders, which are themselves dangerous predators. Here I review several aspects of the predatory behaviour of S. giraffa to argue that, unlike many web-invading araneophagic species, its primary predatory strategy is based on stealth. Going unnoticed in a spider web is a difficult task for an insect because the web acts as an extension of the spider's sensory system. Despite encountering substantial variation in web type and spider behaviour, S. giraffa can successfully adjust its behaviour to prey upon several distinct spider species. This supports the idea that dangerous prey can act as selective factors that favour flexibility in predators. Further, I suggest that the complex behaviour of S. giraffa can emerge from a simple set of seemingly ‘hardwired’ yet flexible rules that are principally guided by sensory systems. Still, other details in the behaviour of S. giraffa suggest that its ability for flexible problem solving could also involve cognitive processes that can fine-tune an innate predatory strategy. As part of this special issue honouring Bill Eberhard and Mary Jane West-Eberhard, I also briefly illustrate how detailed observations of behaviour are essential in disentangling hypotheses about the predatory strategy of araneophagic species.