In The Home of Spiders
“I suppose it’s quite a lot of spiders…” Alistair McGregor says casually, rotating his hand to catch a plump, leggy female who is making a bid for freedom. “We can never have too many though – they eat each other.”
It is in the spider room at his lab in Oxford, home to 10,000 American house spiders and a menagerie of other disturbing animals, from centipedes to tarantulas. The air is deliberately musty, to emulate the dark corners they like to lurk in, and the walls are laden with shelves upholding row upon row of glass jars, tanks and petri dishes.
“Sometimes the crickets escape and we can hear them singing in the corridor,” McGregor chuckles – then quickly follows that they’ve never had a spider on the loose. (His students later tell me that this happens regularly.)
The room is fronted by an appropriately heavy-duty door, like the hatch of a submarine. Being old, sometimes it gets stuck and his students then get trapped inside.
Keeping one eye on the exit, I pick up a jar and look inside. A single spider is reclining on a silvery mat of silk. Eight gangly legs poke out from under her perfectly rounded globe of a body; it’s so unwieldly, it looks more like a marble that has rolled over and crushed her. “They usually have a male in there too, but she must have got to him already,” says McGregor.
Some spiders can use their hairs to listen in on you from across the room. Others can camouflage their bodies to look exactly like a leaf. At least 18 kinds can swim and catch fish, while the brown recluse spider boasts potent, flesh-rotting venom (and a penchant for hiding in bedsheets and shoes).
But the only talent McGregor’s arachnids, Parasteatoda tepidariorum, have is for producing inelegant, three dimensional webs. “They evolved more recently than the ones that produce symmetric webs,” he explains, as though this somehow excuses them. Instead they produce the creepy wisps of silk that hang over chandeliers in horror movies.
Nevertheless, they are not to be underestimated. The most frequently encountered spider in North America is surprisingly effective at snaring insects, and individuals are regularly seen dragging pieces of debris into their webs to hide behind. When they sense a catch, they throw more silk over their victim and draw it up into their mouths. Then they drain its body fluids, leaving an empty husk of a body behind.
But McGregor’s spiders aren’t just here to scare journalists. In recent years, scientists have been moving away from a long-established reliance on the stars of medical research, such as fruit flies and mice, to embrace a new range of bizarre creatures, including near-invincible microscopic animals and fish which can hunt on land.
Spiders may soon be part of this trend too. In fact, they’re ideal research subjects, for two reasons. The first is that they share a genetic secret with humans.
Though we’re separated by upwards of 800 million years of evolution and they don’t even have a proper heartbeat, spiders and humans are remarkably similar. We already know that, for example, spiders use the exact same gene as us, Pax-6, to make their four pairs of beady eyes. Take this ancient gene from a human and replace it with the spider version, and the real-life spider man you’ve created will grow normal, human eyes.
Of course, many animals, from cats (90% of genes in common) to cows (80% of genes in common) are much more ‘human’.
There’s one way spiders have a pressing advantage, however. Way back in their evolutionary history, an ancient spider accidentally made babies which had two full sets of genetic instructions, instead of one. This is a big deal. It happens all the time in plants, but it’s only known to have happened five times in the entire history of the animal kingdom. And two of these occurred in the ancestors of all vertebrates, including humans.
On the face of it, having an extra copy of every gene sounds like a really, really bad idea. After all, Down’s syndrome is caused by a single extra chromosome. But they are actually a major driving force in evolution. While the first copy must carry on with its original function, the second copy is freed up to take on a new role. In the early ancestors of vertebrates, they’re thought to have helped to turn soft tissues, such as cartilage, to bone.
By studying spiders, McGregor’s team is getting to grips with the consequences of these rare events more generally. Which brings us to the second reason they’re so useful. Many of these bonus genes play an important role in early development; to study their function, the scientists need embryos.
Here, spiders can’t be beaten. Arachnophobes may wish to skip this next paragraph, unless they’d like to know that a single female house spider can produce up to 400 eggs every five days. They’re perfectly translucent, allowing scientists to watch the development of the embryos inside without killing them.
To make sure he has a constant supply, McGregor’s lab is basically a breeding program for spiders. It all starts with a silken cocoon, which is woven by an expectant mother in the early hours of the morning. The eggs are fertilised as they’re laid (unlike in some spiders, which fertilise their eggs in the ovaries), so each one is at the exact same developmental stage – very useful if you’re a scientist.
Each cocoon is given its own petri dish and left to develop for 10 days. When they first emerge, baby spiderlings are immobile, hairless and translucent, except for a dash of red in their eyes.
But within a few days, they already resemble their terrifying parents. The petri dish becomes a wriggling, fuzzy mass as they begin to move around, produce silk, and cannibalise their siblings.
This is where it gets a bit tricky. It’s great that they snack on each other, because they don’t need to be fed. However, left to their own devices, eventually each dish would boil down to one very fat spider. Instead a few lucky survivors are separated out into their own private quarters.
From then onwards they’re fed on a banquet of flies – conveniently, the other half of McGregor’s lab studies fruit flies – and crickets supplied by pet shops. Eventually, after several rounds of growth and shedding their hard, outer shells, they’re about 9mm long and ready to mate.
My host looks contemplatively at a vial of spiders. “I’m just wondering, are they mating, or is she about to eat him?” he says. In the wild, suitors tend to run away afterwards (in contrast to male red widow spiders, which force-feed themselves to their girlfriends by repeatedly placing themselves into their mandibles), but in such close confines, it rarely ends well for them. Luckily, most spiders only need to mate once.
Today McGregor’s entire brood is descended from just 10-20 individuals collected from Göttingen, Germany. “When scientists speak at conferences, they tend to show slides of where they collected their animals – usually beautiful islands and beaches,” he said. “We collected ours from a student’s basement.”
Though spider research is barely more than a decade old, it’s already led to some fascinating insights into so-called “gene duplication”. One example is kneecaps.
To begin with, a group of scientists based at Georg-August-University in Göttingen wanted to know why some spiders have relatively short legs, while others have the blood-curdling, spindly kind. They turned to a gene which would surely hold the answer: the Dachshund gene, which is named after the stumpy-legged Dachshund dog.
The scientists compared two common house guests, American house spiders and the aptly-named daddy long-legs – which gives spiderphobes across the globe the shivers thanks to its extravagantly long limbs. They looked for differences in the gene – but they didn’t find any.
Instead, lo and behold, both spiders had an extra copy. To find out what the gene was up to, the scientists turned it off in the American house spider embryos. The mutant spiders were born with their knees fused to their legs, in one single segment – they didn’t have any kneecaps. The structures that allow spiders to scuttle across the bathroom floor, or delicately pick their way across a sticky web, evolved thanks to a big evolutionary mistake.
And there have been other breakthroughs. In the last few years, spider research has provided clues to conditions as diverse as heart disease and ageing, while proteins found in their venom may one day treat brain damage, muscular dystrophy, and even impotence.
I’d like to say I’ll never look at their hairy bodies, eight eyes and fangs the same way…. but, no, I’m sorry. They’re still creepy.
Based on a writing by