Frisky male black widow spiders shake their abdomens to produce carefully pitched vibrations and avoid attacks by females, according to new research published in the open access journal Frontiers in Zoology.
Researchers recorded the vibrations made on webs by male black widow spider (Latrodectus hesperus), hobo spider (Tegenaria agrestis) and prey items. They found that black widows vibrated their abdomens, producing very different sounds to other spiders and to prey items. The researchers played the recordings to females and found that they were much less likely to attack sounds made by black widow males. No spiders were harmed during this experiment – males were kept safe from the females at all times!
Whenever male spiders step on females’ webs to make their romantic approaches, they create vibrations which the females feel. The females use vibrations of the web to detect their prey, and so for males, making advances is risky business – they might be attacked by a female if she thinks they are potential prey.
Catherine Scott, one of the article’s authors, says: “The web functions as an extension of the spider’s exquisitely tuned sensory system, allowing her to very quickly detect and respond to prey coming into contact with her silk. This presents prospective mates with a real challenge when they first arrive at a female’s web: they need to signal their presence and desirability, without triggering the female’s predatory response.”
The scientists recorded the vibrations produced by males of both species, and those produced by common prey items, and compared them. They found that black widow courtship signals differed more from prey vibrations than hobo spider courtship signals did. Black widow males vibrating their abdomens created vibrations with a distinct form to those made by prey items, and also at an especially low-amplitude – much quieter (see the below Notes to Editor for links to videos).
They then played the recordings back to female black widow to see how they reacted and found the females were more likely to attack when they heard 'loud', prey-like vibrations, but were less likely to respond to 'quiet' male-like vibrations. The scientists think this research could open up lots of interesting angles for studying the interactions between male and female spiders.
Scott says: “One of the most exciting things we saw was that sometimes, female black widows actually responded with abdomen ’twitches’ when we played low amplitude ’whisper-like’ vibrations to them through their webs. These abdominal movements by the female undoubtedly transmit their own vibrations through the web. While this study focused on how males communicate to a female that they are not a meal, but a potential mate, it would be very interesting to look more at the female’s behaviour, and any signals she may be transmitting back to the male.”
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Notes to Editor
A meal or a male? The 'whispers' of black widow males do not trigger a predatory response in females
Samantha Vibert, Catherine Scott and Gerhard Gries
Frontiers in Zoology 11:4
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Videos of the spiders can be found in this Dropbox. Please credit all films to Samantha Vibert and all pictures to Sean McCann.
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