coverspider

Spider Moms: The Family Lives of Arachnids

In the (fantastic) 1990 horror movie Arachnophobia, Jeff Daniels and John Goodman do battle with a horde of invasive Venezuelan spiders for the soul of a small California town. It’s a great mixture of gross-out, horror, and comedy — although makes for extremely uncomfortable viewing for an arachnophobe.

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In the film, a research expedition to Venezuela returns to California with an unwanted hitch-hiker, an aggressive and venomous tropical spider. After completing its illegal immigration, it seeks a green-card by mating with a domestic house spider. The house spider gives birth to infertile babies with poisonous bites that run rampant throughout the town (creating scenes like this one, which for a boy was both titillating and absolutely terrifying).[1]

These small, infertile spiders — intones the mandatory expert scientist — are just preparing the way for the real invasion. The male spider, now called the ‘general’, has produced a queen with which to mate (I don’t know how – spontaneous generation?). This mating will produce fertile offspring, which would be bad news for all of America. Luckily, Daniels and Goodman team-up to hunt down and exterminate the nests before they hatch — contending, along the way, with the aggressive general and the queen who are protecting the nests.

Now, I’m not one to get all Neil DeGrasse Tyson, because it’s tedious in the extreme when a scientist gets preachy about inaccuracies in fiction; but I could always take comfort in the knowledge that generally, spiders don’t work together as families, and don’t actively protect their young, and are generally pretty anti-social. So I never had to worry about evil queen spiders tenderly coaxing thousands of little spiderlings into the world with their eight motherly arms.

I'm trying to temper the nightmare-inducing images that could populate this post. Credit: popgive.com

I’m trying to temper the nightmare-inducing images that could populate this post. Credit: popgive.com

Then I opened my email this morning to find a paper called “Maternal care and subsocial behaviour in spiders”, by Eric Yip and Linda Raynor of Cornell University, and now I don’t know what to believe.

Most spider species (and there are many — over 44, 000 have been described), are what Yip and Raynor call “opportunistically cannibalistic”, which is fun to say, but is nonetheless an undesirable trait in friends, family members and sexual partners. When they’re not actively consuming one another, some species may form fragile alliances where they share in the duties of building or maintaining webs — but they’ll still try to eat one another when their backs are turned. I’ve always thought a spider would be a sensible, honest emblem for political parties.

Yip and Raynor, in their far-ranging review, point out that spider social behaviour is a little friendlier than that (some of the time). Some spider families display “subsocial” behaviour, which sounds like an insult, but really means that they aren’t social all of the time, just occasionally, when there is nothing good on TV. In these subsocial species, mother spiders invest a lot of time and effort into their offspring. They guard egg sacs, and sometimes attach the eggs to their backs with silk and carry them around.[2]

And back to nightmares.

And back to nightmares.

But this maternal care can also extend past-birth. Spider moms may catch prey, and regurgitate it for its babies. For some reason this seems totally okay when birds to do it, but horrific when spiders do it.[3] Baby spiders, when hungry, wave their tiny little baby spider legs in the air to let mom know that they need to be fed. Momma spiders also fulfill the other standard maternal role — chasing off predators (which includes John Goodman dressed as an exterminator – if you’re looking for a niche Halloween costume).

john-goodman-arachnophobia

In most animal species where mothers put a lot of time and energy into caring for their offspring, biologists generally argue they do it in order to ensure offspring survival, and thereby get a good return on their investment (daddy spiders, like so many other animals, exit the picture immediately after mating). But in spiders, the moms might be a little more self-interested. Remember that “opportunistic cannibalism” thing? The first meal of many baby spiders is…mom, a behaviour called ‘matriphagy’.  No wonder they go to the effort of providing food — if they don’t,  they’re on the menu. Ungrateful kids.

Featured photo by Thomas Shahan

Literature Cited

Yip, Eric C., and Linda S. Rayor. “Maternal Care and Subsocial Behaviour in Spiders: Subsocial Spider Review.” Biological Reviews (October 2013): n/a–n/a. doi:10.1111/brv.12060.


[1] A few years ago at a field site in Belize I was showering, and hadn’t poked around too much in the shower stall before hopping in. A large, hairy spider fell off the shower head when I turned on the water, and half-swam/half-ran down my torso. Life imitating art (though this was a little less titillating, and a lot more terrifying).

[2] Working in a lab once, I saw a small brown spider scurrying across the floor, trailing a white blob behind her on a piece of silk. “Oh no,” said my hapless friend, “She has a piece of styrofoam stuck on her. I’ll help.” He leaned down, and pinched the white blob. Which, of course, was not a piece of styrofoam, but an egg sac. Out burst hundreds of tiny little spiderlings, and that was the end of working in that lab for the day.

[3] The discussion of regurgitation in the paper is fantastic, if only for this sentence alone: “Regurgitation is ubiquitous in eresids and common in theridiids. It has also evolved once in lycosids and once in uloborids.” I think Dr. Seuss had a hand in naming spider families.

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