Biology of Stenolemus giraffa (Hemiptera: Reduviidae), a web invading, araneophagic assassin bug from Australia

This is the first description of the natural history and behaviour of Stenolemus giraffa Wygodzinsky, an emesine assassin bug (Reduviidae; Emesinae) from Australia. Field data from sites in the Northern Territory and Western Australia, complemented by observations from staged predatory interactions in the laboratory, show that this species is a web-invading araneophage. In the field, S. giraffa was found on rock escarpments, associated with 10 spider species. Spiders of the genus Trichocyclus (Pholcidae) dominated this species' natural diet at all field locations. Predatory sequences appear to emphasise stealth and were characterised by S. giraffa slowly stalking the resident spider until within striking range. Stenolemus giraffa approached the spiders by breaking silk threads in its path while walking across the rock substrate beneath the web or hanging directly from the web. Observations of S. giraffa being attacked, and sometimes killed, by spiders illustrate that araneophagy is a dangerous strategy for these insects. Natural history and behaviour of most emesine species is currently unknown and so the present study provides an important landmark. Findings from this study add to growing evidence that araneophagy is prevalent in the emesine genus Stenolemus and that considerable variation in predatory tactics occur within this genus.