Insects can see ultraviolet light and are known to identify important food sources and mating sites by sensing the characteristic patterns of ultraviolet light that these things reflect  Insects are also attracted to Glomosus spiderwebs, which reflect ultraviolet light
Thus, insects are probably attracted to these webs because of the specific patterns of ultraviolet light that these webs reflect
When the silks of spiders that spin silk only for lining burrows and covering eggs were illuminated with white light containing an ultraviolet component, the silks of these spiders reflected ultraviolet light.