You don’t pick up a name like “assassin bug” without earning it, and the deadly Stenolemus giraffa is certainly deserving of this fearful moniker. Known to feed on a range of different insects, this killer arthropod is particularly famous for its ability to creep up on spiders and devour them in their own webs – and the secret to this incredible stealth has now been caught on camera.
Spiders are incredibly sensitive to any vibrations picked up by their webs, and use their silky homes as an extension of their own sensory system in order to detect any invaders. Yet assassin bugs are somehow able to intrude on spider webs without setting off any alarms.
To try and figure how they avoid detection, Fernando Soley from Macquarie University in Australia filmed an assassin bug as it made its way across a spider’s web, using laser vibrometry to pick up any vibrations it generated.
As the video shows, the insect grabs the threads of silk and breaks them with its front legs. Describing this technique in detail in the journal Royal Society Open Science, Soley explains how the predator “attenuates the vibrations produced by holding on to the loose ends of the broken thread and causing them to sag prior to release.” It is also careful not to release both ends at the same time, in order to further diminish vibrations.
The clever assassin also often waits for gusts of wind to ripple through the web before advancing, in order to camouflage its own vibrations and minimize the possibility of arousing the spider’s suspicions.
As a result of these sneaky tricks, Soley was barely able to detect any vibrations in the web at all, which shows how little chance a spider has of saving itself from this deadly intruder.