How Spiders Fly Like Rockets and Other Mysteries
The ways spiders' bodies work and minds think reveal a secret world known to only a select group of scientists.
Like many of you, I’m terrified of spiders. James O’Hanlon wrote Eight-Legged Wonders to explain why we shouldn’t be.
O’Hanlon is an arachnologist who has collected the most interesting facts about spiders and broken down their most fascinating behaviors. Spiders have diverse hunting techniques, and they’re impressive strategic thinkers.
This is a rare — and picture-free — look into the world of spiders, from the largest to the smallest.
Small Spiders, Giant Webs
About halfway through the book, O’Hanlon introduces Darwin’s bark spider. It’s an orb-weaver spider that’s only 22 millimeters long. But its webs are much larger:
“When the team of scientists headed to Madagascar in search of Darwin’s bark spiders, they measured webs spanning rivers up to 82 feet across. To put that into perspective, that’s longer than a semi-trailer, half the width of a football field, or five times as long as a giraffe is tall.”
Darwin’s bark spiders build their webs across rivers to catch insects in bulk. As impressive as those webs are, the material supporting them is even more impressive:
“Darwin’s bark spider silk was twice as tough as any spider silk — it absorbed 10 times more kinetic energy than bulletproof Kevlar. They hadn’t just discovered the toughest spider silk; they had found the toughest material produced by any living creature on the planet.”
It’s no wonder that scientists scour the jungle looking for spiders and their giant webs. A material stronger than Kevlar and lighter than air would be a monumental breakthrough in personal protection. Even spider venom is studied for possible medical applications.
Spider silk is interesting, but other spider traits are more difficult to explain.
Creative Ways to Die After Sex
Among spiders, females are larger than males. Many males are so much smaller that they can crawl on a female’s back unnoticed. Some male spiders distract females with a snack so they can crawl on the busy female’s back and deposit sperm. These males survive to mate another day.
Others not only get eaten. They sacrifice themselves willingly. Some even flip into the female’s jaws while they’re mating. It doesn’t make sense from a life-affirming point of view, but it makes more sense from an evolutionary one.
In The Extended Phenotype, Richard Dawkins explains the gene’s eye view of the world. Genes are successful when they’re passed on across generations, and they can’t do that if the organisms that genes ride in die too soon. As long as a behavior improves the chances of passing genes onto the next generation, it can be selected for even if it kills the organism. O’Hanlon gives an example:
“Male red-back spiders who volunteer themselves up for cannibalism mate for longer, which gives them more time to transfer sperm into the female. This then leads to a greater likelihood that his sperm will be used to fertilize her eggs. In the spontaneously dying dark fishing spiders, females who cannibalize males lay almost twice as many eggs that hatch larger offspring compared to females who didn’t cannibalize males. So the male’s sacrifice could lead to him fathering more and better-quality offspring.”
The behaviors that result from the spider’s genes are designed for procreation, not for giving spiders the longest lives.
Females aren’t immune, either. One species of female spider liquifies her insides as her babies hatch. By the time her hatchlings grow enough to form mouths, the hatchlings can drink their mother’s liquified insides. It’s an early meal that’s crucial for their development — and for surviving long enough to pass their genes on.
Tiny Rocket Ships
One of the best recent discoveries about spiders is how they fly.
The old theory was that spiders spun a balloon or a sail with their silk to ride the wind. However, that didn’t explain how quickly spiders took off or the directions they would fly in.
In 2018, two professors discovered how spiders really took off. They put spiders in an enclosure with no wind but an electric current that could be turned on and off:
“As soon as the electric field was switched on, the spiders adopted the stereotypical “tip-toe” posture that preceded ballooning, suggesting that the spiders could detect the presence of the electric field. The spiders then started releasing silk and, inside a completely windless chamber, lifted off the ground.”
“Negatively charged spider silk was repelled by the similarly charged metal plates on the floor and drawn toward the positively charged particles in the air. Morely and Robert even found that they could control the spideres’ ascent or descent by simply switching the electric field on and off. Spiders don’t balloon: the launch on electromagnetic silk rockets.”
The spider’s eye view of the world is a fascinating one. O’Hanlon’s book is a must-read for anyone interested in spiders — especially those of us who don’t want to get too close to them.