Spiders have grown big – and now they’re heading indoors

by Alice Roberts

Professor of Public Engagement in Science at the University of Birmingham

The spiders in my garden this season have been huge. There’s one in particular that’s set up home in a rather unkempt lavender bush, weaving itself an oversized – but still beautiful – web.

This huge spider has stripy legs and a big, chunky brown body decorated with an ornate pattern including white spots in a cross. It is a quite beautiful specimen of Araneus diadematus. The web is a classic spider’s web. Now, spider webs come in many shapes and sizes: different spiders spin their silk and weave it into sheets, funnels and that classic pattern with spokes and a spiral of silk joining them all together. This last one is what a child would sketch if you asked them to draw a spider web. It’s an archetype. Although not all spiders make webs like this, it’s the one that really captures our attention, probably because it is so aesthetically pleasing.

Video of Larinioides cornutus building a web

But these webs are also consummate pieces of engineering (indeed, spider silk itself is such an extraordinary material that it has become a focus for scientific research). The classic spider web is the hallmark of the orb spiders, including our common (or garden) orb-weaver, Araneus diadematus. So the specimen in my garden is not an exotic creature; she’s very ordinary, in fact, but she has managed to reach an extraordinary size. In fact, she seems hardly able to move her massive bulk around her web.

It’s very likely that you’re reading this and thinking, Yes! I have seen some very large spiders this year! Well, you and I are not alone in noticing this phenomenon; it’s even made headlines in some other newspapers. Perhaps not surprisingly, it’s likely that the reasons for such large spiders are quite mundane. Spiders are always big in the autumn: they’ve had all summer to grow. And this summer was particularly lovely and warm – not just for us, but for spiders and their insect prey as well.

Wasp spider Argiope bruennichi on its web in Cornwall

Spider growth is not unlimited, but in such conditions, more of our spiders will be reaching their maximum size. And some of them will be heading indoors. And why not? For spiders whose ancestors have spent thousands of years finding cosy, warm and dry homes in burrows, small caves and hollow trees, a 21st-century, dry and heated house must be irresistible. How kind of us humans to build such a thing just for them! Just so they can come inside, as the weather’s getting less clement, and try to find a mate. Headlines have been less conservative. We’ve had: GIANT SPIDERS TO INVADE UK HOMES THIS AUTUMN, WARN EXPERTS, with regional variants, such as: LARGE SPIDERS TO INVADE HULL THIS AUTUMN and GIANT SPIDERS SET TO INVADE CHELMSFORD AND ESSEX, and, in Scotland, INVASION OF THE SUPER SPIDERS.

Now, I find these headlines amusing. But I also know that they’re written in order to stir the emotions of any of us who might be, well, just a little bit of an arachnophobe (as against its antonym, arachnophile). And that includes me – or at least, it did. Until I filmed a programme called Spider House for BBC4*. I was stuck in a house for a week: a house that was filled to the brim with spiders, ranging from ordinary garden orb-weavers to their more exotic cousins, the tropical orb-weavers. I learned so much about spider biology that I managed to replace some of the fear with fascination. But I have to admit there were aspects of spider biology that made them seem even more alien, and even harder to love. A spider breathes through a slit in its abdomen, drawing air into “book” lungs, made of densely folded membranes. They don’t have blood as such; they have something that is like blood and tissue fluid combined – it bathes their internal organs and isn’t kept inside blood vessels. And what about digestion? Spiders eat their food by pumping digestive enzymes into it, and sucking up the liquid.

Male striped lynx spider showing enlarged pedipalps

Finally, spider sex. You may have noticed a pair of dangling appendages in front of a particularly large house spider’s head this year. Those appendages are not legs, and they’re not antennae. They’re called pedipalps, and they are, in fact, what a male spider uses to transfer sperm to a female. Let’s just leave it there.

So I think what’s probably happened is that I’ve managed to replace some of my fear of spiders with a modicum of disgust. But I do admire them too. I know they’re doing a brilliant job of keeping insect pests down, and I almost love them for it. Indeed, I love the webs my garden orb-weavers weave, and they’re quite pretty, too – even when they come into the house. But that house spider, that Tegenaria gigantea scuttling across the floor... I know he means no harm, and I don’t wish him any harm, but I do wish he would find some old tree or little cave to live in, rather than my house.

*Spider House was aired by BBC4 on 29 October 2016, at 9pm.

European garden spider (Araneus diadematus) whose web is a 'consummate piece of engineering'

Check out these interesting articles by/on Dr Richard J. Pearce, an arachnologist and animal ecologist writing on behalf of the British Arachnological Society (BAS):