Effects of size, motility and paralysation time of prey on the quantity ofvenom injected by the hunting spider Cupiennius salei

Previous experimental studies have shown that neotropical wandering spiders (Cupiennius salei) inject more venom when attacking larger crickets. It ha s been postulated that this is a consequence of predator-prey interactions during envenomation, which increase in intensity with the size of a given p rey species. The present study was designed to test this hypothesis using a naesthetized crickets of different sizes that were moved artificially. Cupi ennius salei was found (1) to inject more venom the greater the intensity o f the struggling movement of the crickets (prey size kept constant); (2) to inject more venom the longer the duration of the struggling movement of th e crickets (prey size and intensity of movement kept constant); and (3) to inject equal amounts into crickets of different size (duration and intensit y of movement kept constant). These results indicate that C. salei alters t he amount of venom it releases according to the size and motility of its pr ey. Venom expenditure depends mainly on the extent of the interactions with the prey during the envenomation process, whereas prey size is of minor si gnificance. The regulation of venom injection in concert with behavioural a daptations in response to various types of prey minimizes the energetic cos t of venom production, thus increasing the profitability of a given prey it em.