No matter how much we benefit from spiders (like hunting and eating agricultural pests), many of us are still creeped out by them. We know they do good, we know that they (generally) mean us no harm, but for some reason we just can't firmly grasp that. For all they do to help our environment, spiders still just freak us out.
And, depending on who you are, the most recent study of spiders may either make you appreciate them a little more or just may be the stuff of nightmares...
Dr. Lena Grinsted, Senior Lecturer in Zoology at the University of Portsmouth, examined how spiders hunt together and what effect that has had on their evolution. She and her fellow researchers have developed a "prey to predator size ratio hypothesis" which makes the case that large spiders that started to live and hunt as a group would slowly evolve to a smaller body size.
Dr Grinsted explains, “Perhaps the most intriguing consequence of this new hypothesis is the suggestion that working together relaxes selection on body size on relatively large spiders. Our argument is that when these spiders start cooperating in catching prey, they can still catch the same really large prey, even if they start to mature at a smaller body size. And a smaller body size carries with it multiple overall fitness benefits when you live in a crowded group.”
First, smaller body sizes means that fewer resources are needed for each spider to mature, which leads to less competition for limited resources within a colony. So a single large insect can go a long way, feeding many of the group’s inhabitants.
Second, although smaller body sizes are accompanied with the production of fewer eggs per female, social spiders invest in quality over quantity of offspring, producing much fewer but significantly larger eggs than their non-social contemporaries.
Last, the ability to mature at a smaller size allows for some level of flexibility as a response to unpredictable environmental conditions. For example, when there are fluctuations in the number of prey available, females may be able to mature at very small sizes and still successfully raise some offspring with the help from other females in the colony, despite producing only very few eggs.
Dr Grinsted continues: “By analysing data on body sizes from lots of spider species and the size of their insect prey we found very strong support for our new theory, the ‘prey to predator size ratio hypothesis.'"
“When spiders evolve the ability to catch prey cooperatively, we see a beneficial increase in the prey:predator body size ratio. This increase can be achieved either by catching larger prey, as the classic theory suggests, or by evolving a smaller predator body size, as we see has happened in some social spiders."