Stenolemus

Abstract: Stenolemus bituberus is an araneophagic “assassin bug” (Heteroptera; Reduviidae; Emesinae) that typically is found living in spider webs. We documented the life history of S. bituberus in the field for 13 months, determining its developmental phenology and microhabitat characteristics as well as describing its mating and predatory behaviour. We also included a morphometric analysis of the instars. Our study revealed that S. bituberus is univoltine with five juvenile instars. Although S. bituberus is found in the webs of spiders from a wide range of genera, it is found most commonly in the webs of Achaearanea, Badumna, Pholcus, and Stiphidion. Multiple juveniles often were found on a single web, but adults tended to be more solitary. Stenolemus bituberus appears to have two distinct hunting strategies: “stalking”, in which they slowly approach the spider, make contact and then strike; and “luring”, in which they attract the spider within range by manipulating the silk with their legs.

Abstract: Some predators sidestep environments that render them conspicuous to the sensory systems of prey However, these challenging environments are unavoidable for certain predators Stenolemus giraffa is an assassin bug that feeds on web-building spiders; the web is the environment in which this predator finds its prey, but it also forms part of its preys' sophisticated sensory apparatus, blurring the distinction between environment and sensory systems Stenolemus giraffa needs to break threads in the web that obstruct its path to the spiders, and such vibrations can alert the spiders Using laser vibrometry, this study demonstrates how S giraffa avoids alerting the spiders during its approach When breaking threads, S giraffa attenuates the vibrations produced by holding on to the loose ends of the broken thread and causing them to sag prior to release In addition, S giraffa releases the loose ends of a broken thread one at a time (after several seconds or minutes) and in this way spaces out the production of vibrations in time Furthermore, S giraffa was found to maximally reduce the amplitude of vibrations when breaking threads that are prone to produce louder vibrations Finally, S giraffa preferred to break threads in the presence of wind, suggesting that this araneophagic insect exploits environmental noise that temporarily impairs the spiders' ability to detect vibrations The predatory behaviour of S giraffa seems to be adaptated in intricate manner for bypassing the sophisticated sensory systems of web-building spiders These findings illustrate how the physical characteristics of the environment, along with the sensory systems of prey can shape the predatory strategies of animals

Abstract: 1. Animals, as they move through their environment, leave traces of their passage that can be informative to others and convey significant advantages to the animal producing them. However, such traces may also reveal presence, location or identity to enemies. 2. We studied an araneophagic (‘spider-eating’) assassin bug, Stenolemus bituberus (Heteroptera, Reduviidae), testing whether it associated with areas containing chemotactile traces (e.g. draglines, excreta) left behind by nine sympatric spider species. Stenolemus bituberus were presented with a choice between a substrate containing draglines and a clean substrate. Each hour, for a duration of 12 h, we recorded which substrate was occupied. 3. Stenolemus bituberus tended to associate especially with draglines left by spiders from the genus Achaearanea, their most common prey in nature. 4. These results suggest that S. bituberus exploits draglines from these spiders as cues for indicating prey presence. We also found an increasing tendency to associate with draglines from some spider species through the day, which may be related to circadian patterns or slower response times of some individuals.