A spider\’s greatest weapon, its web, is being used against it.

Sydney scientists have uncovered the way insects named, rather aptly, assassin bugs can mimic the vibrations of prey caught in a web, luring the spider to within striking range.

A Macquarie University biologist and co-author of the study, Phil Taylor, said spiders determine what has been caught from the frequency and duration of vibrations on their webs. Male spiders also shake their web to attract fertile females.

To work out the assassin bugs\’ ploy, the researchers stuck various objects onto the webs of spiders kept in a laboratory, measuring the vibrations and the spiders\’ reactions to them. Leaves dropped onto web prompted no approach. When male spiders started courtship vibrations, the females adopted a mating position.

\’\’The distinctive response of spiders to leaves and courting males indicate that they can readily discern differences between these stimuli,\’\’ said the authors, whose findings are published in the journal Proceedings of the Royal Society B.

Associate professor Taylor said the bugs generated vibrations similar to those generated by prey, such as aphids and flies, as they struggled to free themselves. Most spiders changed their orientation to face the source of the vibration before approaching it.

Assassin bugs move over a web and pluck the strands without sticking to it, due to the design of their feet.

\’\’To a spider, the vibrations generated by bugs may resemble small or exhausted prey that cannot … struggle,\’\’ said the authors.

Once the spiders are close enough, the assassin bugs raise their upper body, lunge forward and impale the spider, injecting venom at the same time.

\’\’The spiders just drop dead like a bag of potatoes. It is quite frightening to watch,\’\’ said associate professor Taylor.