Spiders aren't scary villains but nature's most resourceful engineers

Spiders are not everyone’s cup of tea. Their eight legs, their many eyes, and their tendency to lurk in the shadows causes unease and sometimes fear in many of us. Films like Arachnophobia, Harry Potter and the Chamber of Secrets, the Lord of the Rings: the Return of the King, and King Kong all play to this fear. But this is just fiction. Spiders are in fact wonderful, although I fear this article might not entirely convince you.

My favourite spiders are jumping spiders called Portia. Most species are small, with females growing to no more than 10mm across. They also hunt in remarkable ways, which has led to many people claiming they are the cleverest of all spiders, although whether any animal with a brain of a few tens of thousands of brain cells can be termed clever seems unlikely. Females have been observed spotting an orb-weaving spider, sat in its web, and working out how best to approach it. They plot a route to a twig or leaf above the spider they want to eat and steadily make their way there. They then descend a silken thread before pouncing on their hapless prey, injecting it with venom. The innards of the incapacitated victim are then sucked out and consumed. This is not the only way they hunt. Females of some species have been observed spending many hours drumming out a beat on a silk thread of a web of a spider they wish to kill. They eventually find the magic rhythm, with the web’s owner homing in on the beat, believing they have trapped a fly, only to meet their end.

Most species of spider are solitary, but a few are social, sharing large webs. African social spiders, of which there are a few species, are remarkable. They can form colonies of up to 2​,000 individuals, and they spin vast communal webs. Only about 40% of the females in a colony mate, but all help to look after the young. The final act of each female is to sacrifice herself to the spiderlings, with the brood hungrily consuming the mother or aunt. Evolution has favoured this behaviour, presumably as the loss of the female to help her relatives thrive is a more successful strategy than the brood going hungry and the spider living to a greater age.

If the thought of 2​,000 spiders living together in a giant web gives you goosebumps, then you might feel quite queasy reading about a find in a cave close to the Greek-Albanian border. The cave wall is covered with bacteria feeding on sulphur compounds found in water that drips down it. These bacteria are food for tiny animals that are fed upon by midges, with the spiders feeding on these abundant insects. There are estimated to be over 110,000 of them living together in a giant tangle of web stretching over 100m. What is even more remarkable is there are two species of spider living together in this spider megacity: domestic house spiders and a species of sheet weaver. Outside of the darkness of the cave, the house spiders would normally prey on the sheet weavers, but it has hypothesised that they do not realise they are there because of the pitch black. I love it when scientists make new discoveries like this, changing our view of how animals can be flexible in how they live their lives.

These two species of spider are harmless to humans. In fact, most spiders pose no threat at all. Rather, through killing insect prey, some of which can spread disease if they bite us, they are beneficial. Globally there are only a few species of spider that have bitten people who have subsequently died from the bite including the Sydney funnel-web, the Brazilian wandering spider, black widows, brown recluses and the Katipo, but they are thought to kill less than ten people each year.

If spiders give you the heebie-jeebies you should spare a thought to one of the threats that they face. Most species, including tarantulas, are attacked by parasitoid wasps. These insects search out adult spiders, paralyse them with a sting, before laying their eggs on them. When the eggs hatch, the baby wasps burrow into the spider, eating them alive from the inside. The spider only eventually dies when the young parasitoids are ready to emerge and search for a mate, with the females then searching for a spider victim of their own.

If spiders made films, Alien would be a documentary rather than fiction. You might find spiders terrifying but be very thankful there are no parasitoid wasps that prey upon us.

Tim Coulson is Professor of Zoology at the University of Oxford, where he has led both the Zoology and Biology departments. He was previously at Imperial College London and has also held positions at Cambridge University and the Institute of Zoology London. A highly decorated scientist with awards from major institutions including the Royal Society, he has edited leading journals and served on Government advisory boards. His first book for general readers, “A Little History of Everything” (Penguin Michael Joseph), traces the 13.8-billion-year story from the Big Bang to human consciousness and is available to buy on Amazon.

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