Spider 'artist' traps prey with light

The cross shape, zigzag shape or twisted shape on the spider web has long been confusing to observers. New research on spiders Australia discovered that seemingly useless decorative motifs are traps that use light to attract prey.

According to co-author Dieter Hochuli, University of Sydney, Australia, "We really want to find out why spiders invest in their net decoration."

Some researchers suggest that the design is used to warn mammals that are larger than the presence of a net so they don't go or fly in. Others argue that design itself is to lure prey.

This work appears in this month's issue of the Biological Journal of the Linnean Society.

(Photo: National Geographic)

Cheated

Many flowers reflect ultraviolet light that insects use to identify food sources.If spider webs reflect the same type of light, this suggests that spider webs are mimicking the characteristics of flowers and entangled insects.

Hochuli and colleagues coated ultraviolet-filtered plastic onto Saint Andrew's Cross's net in gardens near Sydney University. Then they watched the insects caught daily between plastic-covered webs and uncoated webs.

Flies, bees, wasps and mosquitoes are common victims in both covered and uncoated spider nets. In covered spider webs, the number of these species is reduced.

Mosquitoes and species do not see ultraviolet light, are not affected by the filter layer.

Light trap

The group concluded that the spider web may have formed 'light traps', where the reflection of spider web strands tricked the prey into death.

'Interestingly, spider webs with cross shapes are a bit more complicated than we thought. Spiders seem to take advantage of prey sensitivity with UV rays. When we filter different elements in the spectrum of spider webs, we change dramatically the catch rate. '

Catherine Craig, an entomologist at Harvard University, who is not involved in the study, said, 'This confirms the research I conducted earlier in the field and in the laboratory. UV reflective textures made by this species seem to attract prey. '

The next step is to explore more deeply the effect of this texture itself.