If you're reading this, you probably aren't a spider, and may even have a strong aversion towards eight-legged, web-weaving creepy crawlies – especially giant ones. However, we regret to inform you that spiders of epic proportions are more than just the stuff of fiction, and do indeed walk among us. Even more alarming is that scientists are unable to explain why they are growing to such an enormous size.
The good news is that you're highly unlikely to ever come across one of the giant spiders in question, since they only live in the oceans around the polar regions. Interestingly, gigantism has been observed in a number of other Arctic and Antarctic species, leading biologists to conclude that certain elements of the polar environment must be conducive to humungous body size. However, the quest to decipher exactly why some organisms living at the ends of the Earth become giants has so far not produced results.
Several hypotheses have been put forward, with some scientists claiming that large body size may have developed as an evolutionary trait to enable animals to withstand long periods of starvation during the winter, when resources tend to become scarce in the polar regions. Others have suggested that some of these species may somehow be descended from creatures that invaded the Arctic and Antarctic from the deep sea, where high rates of gigantism have also been recorded.
However, a recent study appears to lend support to a different theory, which revolves around the availability of oxygen in the polar oceans. These waters can hit temperatures of -1.8 degrees Celsius (29 degrees Fahrenheit), and therefore tend to be rich in oxygen, since oxygen is more soluble in cold water than warm water. It has subsequently been suggested that this high availability of oxygen – coupled with the fact that low temperatures slow animals' metabolism down and reduce their need for oxygen – could facilitate their gigantism.
To test this hypothesis, a team of marine biologists drilled deep beneath the Antarctic sea ice, where they encountered a number of giant sea spiders, as can be seen in the video below. Technically, these enormous aquatic critters are not actually arachnids, but belong to a class of arthropods called pycnogonids. Normally they are pretty small, although some can grow to gargantuan proportions, reaching sizes of 50 centimeters (20 inches).
After collecting samples, the team performed a number of experiments in order to determine how changing oxygen levels in the water would affect their subjects. According to Hakai Magazine, the researchers found that placing the spiders in water with lower oxygen concentrations had a negative impact on their wellbeing, thus suggesting that the high availability of oxygen in the cold Antarctic water may well be vital to their ability to survive as giants.
However, this research is far from conclusive, and the team insists that much more work is needed in order to determine the full cause of polar gigantism. In other words, we still don't really know why giant sea spiders exist.