Spider webs are light traps for insects

Spider web reflects ultraviolet light which is visible to insects. [Link]

Ensnared

Many flower species reflect ultraviolet light, which insects use to identify food sources.

If spider webs reflect the same light, it would suggest that the spiders' webs are mimicking the properties of flowers and tricking insects into coming closer.

Hochuli and colleagues coated Saint Andrew's Cross webs in gardens near the University of Sydney with an ultraviolet filtering plastic. They then monitored what insects were caught daily in both filtered and unfiltered webs.

Flies, bees, wasps, and mosquitoes were all common catches on both filtered and unfiltered webs. In filtered webs, the overall numbers of most species dropped.

Mosquitoes, which do not see ultraviolet light, were unaffected by the filters.

Light Trap

The team concluded that the webs may be essentially setting a "light trap," where the reflection of the web strands lure passing insects to their deaths.

"Interestingly, the webs [decorated with crosses] were a little more sophisticated than we first thought," Hochuli said.

"The spiders seem to be exploiting the sensitivity of some prey to UV light in particular. When we filtered different components of the visual spectrum from webs … we dramatically altered prey-capture rates," he said.