The female black-widow spider are several times the size of the male. Have you heard that the females are cannibalistic? You might have since the black widows get their name because it was thought that the females carry out sexual cannibalism after mating; thus the name widow. Actually, in North American black widows performing cannibalism is quite rare, unless the female is really hungry, and in that case she might eat him rather than mate with him. The females are around 15-mm long and are black with a red hourglass-shaped mark on the abdomen. The male is much smaller and is a light tan color with a striped abdomen. Black widows don’t build the uniform spoil-shaped webs that we usually think of when we think of spider webs, but their webs are messy in appearance. The female deposits pheromones which are kind of like chemical personal ads that can provide information about things like the species, sex, age, mating history, and body condition on the silk to attract a male to mate.
When a male black-widow spider enters the spider web of the female, he beings a mating ritual which includes him dancing on the web to transmit vibrations; every few steps he strokes the web again. When he reaches the female, he does such things as stroking her with his front legs. After the display comes to an end, the male cuts large sections of the web and wraps it with his silk. Why do male black widow spiders cut out large sections of the female’s web, and why do the females let him do it? Keep reading.
A study done by postgraduate student Catherine Scott at Simon Fraser University shows that the male destroying part of the female’s web, makes the female less attractive to other males, and therefore, cuts down on rivalry. Competition to mate with the female is very high with maybe around 40 males arriving at a female’s web during one night.
In Catherine Scott's research, she cut out half of the web of a female with scissors. They then brought it into the wild to see if that reduced the amount of suitors. They found that it did not. So what the male is doing is more complex than just reducing the web size. Scott said, “One possibility is that the female pheromone is concentrated in certain areas of the web, and males are bundling up those specific sections with silk, which stops the pheromone from being released. The males could also be adding their own pheromones, which rival males avoid. We didn’t find evidence for a male-silk pheromone in these experiments, but it’s definitely something we want to investigate further.”
One explanation why a female will allow a male to cut out a big section of her web is since a female only needs to mate once to have all of her eggs fertilized, if her web remains intact, it will continue to send out pheromone signals to attract mates. Possibly, this web reduction could be a way for the female to escape being harassed by other males. There probably are still things that are not understood about the web reduction and its role in communication. “Our research reinforces the fact that animal communication is not always as simple as a female producing an attractive signal, then a male following it and finding her; it can be much more complex than that,” Scott said. So there is much to be learned about this small creature! . #blackwidowspider