The assassin bugs’ behaviour is known as aggressive mimicry, say the authors Scientists have described how a species of insect lures spiders by mimicking prey caught in webs.
Assassin bugs plucked the web’s silk threads that replicate the vibrations of a fly or other insect, causing the fooled spider to head towards the bug.
Once within reach, the bug slowly tapped the spider with its antennae before lunging and stabbing the lured arachnid with its sharp snout.
The findings appear in the journal Proceedings of the Royal Society B.
The team from Macquarie University, Australia, said the behaviour – known as aggressive mimicry – was one of two strategies employed by the bug (Stenolemus bituberus) to trap its prey.
“To a spider, the vibrations generated by bugs resemble small or exhausted prey”
Dr Anne Wignall and Dr Phil Taylor Macquarie University
The other involved “stalking” spiders, where the assassin bug slowly approaches the unsuspecting victim until within striking range.
The researchers, Drs Anne Wignall and Phil Taylor, explained that the bug exploited web-building spiders’ use of vibrations to detect and locate its prey.
“However, reliance on vibratory cues and predictable responses leaves web-building spiders vulnerable to predators that aggressively mimic prey stimuli to gain control over their behaviour,” they wrote.
Bad vibes
In their study, the pair set out to compare the responses of spiders to the presence of prey in their webs with the arachnids’ response to the assassin bugs’ behaviour.
“Other vibrations in spider webs include mates and debris, and these were potential models for aggressive mimicry,” they observed.
“Hence, we also compared spider behaviour in response to courting males and leaves falling into the web.”
In their results, the team noted that there were “significant differences” to the various sources of vibrations.
They found that the spiders did not tend to respond to leaves falling on the webs, and female spiders responded to males by “entering a characteristic copulatory position”.
But how spiders responded to the bugs was extremely similar to how the spiders responded to prey, they observed.
“To a spider, the vibrations generated by bugs resemble small or exhausted prey.
“The responses of spiders to prey in the web were occasionally characterised by a direct and rapid approach towards prey without pause (reaching it within one second).”
But, they explained: “This response was.. observed towards bugs or other sources, and may be elicited by the presence of higher frequency and amplitude vibrations in the struggles of prey.”
However, spiders can be a formidable opponent for the assassin bug if they move quickly across the web to the potential predator.
“We have observed bugs being counter-attacked, killed and eaten by the spider they were hunting,” they added. “This risk may be considerably increased when the spider approaches rapidly and without pause.
“Bugs, hence, appear to aggressively mimic a broad class of prey-like vibrations that are effective at soliciting approaches but are also unlikely to elicit highly aggressive, dangerous responses.”
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