Natures wonders: Assassin bugs stalk spiders on webs (Introduction)

by David Turell , Wednesday, October 26, 2016, 23:17 (2948 days ago) @ David Turell
edited by David Turell, Wednesday, October 26, 2016, 23:24

They carefully cross the web with the spider not recognizing the attack until they become lunch:

http://phys.org/news/2016-10-giraffe-assassin-bugs-outwit-spider.html

"Assassin bugs earned their name by stealthily sneaking up on prey and driving their beaks into the bodies of their victims, quickly killing them by sucking out their innards. The giraffe variety has a long neck and survives by sneaking up on spiders in their webs and killing and eating them. But scientists have wondered how the bugs manage the feat without being detected by the spiders. Spider webs are more than just nets used to catch flying insects; they are also transmitters of tiny movements that cause very small vibrations—this is how a spider knows if a bug has been trapped so that it can quickly hurry over and kill it before it escapes. But giraffe assassin bugs somehow make their way across a web without causing vibrations, allowing them to sneak up on their prey.

"To solve the riddle, Soley captured several specimens and brought them back to his lab for testing. He also captured several spider specimens and coaxed them into spinning webs in the lab, as well. He aimed a laser at the webs as the assassin bugs stalked the spiders and filmed the results.The video revealed that the bugs used their foretarsi (tips of front legs) to grab hold of single strands of the web and then to gently pull them apart, tearing the web. The bugs then carefully released the torn strands, avoiding recoil, and moved on to another, making a beeline for the unsuspecting spider. The laser vibrometry sensor revealed that this technique allowed the assassin bugs to make their way to the spider without causing ripples in the web.

"Soley also found that the assassin bugs prefer to stalk their prey when there is a slight breeze (in the lab he used a fan), which causes the web strands to shake, making it more difficult for the spider to detect subtle vibrations. He also noticed that the bugs varied the timing of slicing the web, which made it even more difficult for the spider to sense impending doom."

Comment: This behaviour might have developed by a series of attempts to sneak up, but unless done with the stealth currently demonstrated it was probably mostly fatal. Did lucky ones pass it on? How? Was there observation by bystanders? All seems implausible. Perhaps God helped. Another take says it doesn't always work:

https://www.newscientist.com/article/2110313-spider-eating-bug-muffles-web-vibrations-t...

"This stealth is crucial because a single reckless move can be fatal. In up to 10 per cent of cases, the spider detects the bug and launches a counter-attack, Soley says. “Spiders have silk and venom, so they can work the prey from a distance, bite them and weaken them before finishing the job.”

"The insect’s ability to trick spiders is unusual, says Mark Elgar at the University of Melbourne. “This is interesting because there are numerous examples of spiders using intriguing methods of capturing insect prey, but rather fewer instances of clever ways in which insects capture spiders."