Is The Red “Hourglass” Mark On Black Widows Meant To Frighten Predators?

Black Widows are well known around the world. These spiders are especially known in the Americas for having a highly venomous bite, they are generally intimidating to other arthropods, and the females often kill their male counterparts after mating. And the red “hourglass” marking on the female’s abdomen is a sure indicator that the female black widow is poisonous, right?

Although the strangely shaped red markings located on female black widows has made them famous, what is its actual purpose? Many people have heard that the markings are there to indicate to humans that black widows are venomous. That would be a very gracious tip from Mother Nature herself if only that were true, but it is not. Actually, the red markings located on a female black widow’s abdomen are meant to intimidate, but not all animals are so scared.

According to scientists, as of now we know that the red markings located on the female black widow’s abdomen can effectively scare birds away, but not insects. In fact, it is likely that insects don’t even perceive the hourglass shape in the first place. The visual systems belonging to birds and insects are very different systems. Birds have extra photoreceptors that allow them to perceive the red color on a black widow; an insect cannot boast this remarkable vision. So, now you can just say that the red hourglass marking that you see on a female black widow’s abdomen is for the birds.

Have you ever spotted any type of spider or insect that possessed a brightly colored feature that made it stand out?