Predators who are adept at ambushing tend to combine success or failure in one fell swoop — hiding until the moment of attack. But for crab spiders, taking the initiative and attracting prey is king. In simple terms, they will attract bees by staying on the flowers to reflect ultraviolet light, rather than weaving a large net to "wait for the rabbit".
Felipe Gawryszewski and his team from the Federal University of Goiás, Brazil, collected 68 species of crab spiders from Australia, Europe and Malaysia for study. It was found that all crab spiders adopted an active strategy - crouching, waiting, swooping, all in one go, the difference is that some crab spiders do not choose bright flowers, but choose to crouch on the earthy brown bark or leaves.
The research team analyzed the genetic information of all the crab spiders and made a "family tree" (a kind of map that indicates kinship). As can be seen from the atlas, crab spiders that choose to live on flowers for predation have undergone multiple evolutions and can reflect more ultraviolet light than crab spiders that do not inhabit flowers.
This predation strategy seems to work, as bees do prefer to stay on flowers inhabited by crab spiders that reflect ultraviolet light.
But the reason why bees are attracted is not clear at present, but one possibility is that bees mistakenly regard the "sparkling" crab spider on the flower as a "flower indicator" - natural flowers often attract pollinators through bright spots, like glittering crab spiders.
Another possibility is that perhaps bees have a special fetish for certain color patterns, and crab spiders take advantage of that, Gawryszewski says.
But he also pointed out that there are also flaws in this strategy. "The ultraviolet light reflected by crab spiders can not only attract more prey, but also attract more predators."
Scientists have speculated that crab spiders can reflect ultraviolet light in connection with a predation strategy based on flowers. "The existing study is the first piece of evidence for this speculation on genetic information," says Jerome Casas from the University of Tours in France.