The Spider Mother That Barfs Up Her Guts to Feed Her Kids

Someone get this lady a tiny "Mother of the Year" mug.

Did you know that most of Hawaii’s beautiful sand is parrotfish poop? It’s just one of the many ways that nature goes and ruins things that humans hold so dear. Take motherhood. A human mother is great and sweet and beautiful and hardly ever dissolves her own intestines and vomits them up for her kids until she dies, at which point the young open up her abdomen and consume the rest of her. So … happy Mother’s Day?

Such is the life of the Stegodyphus lineatus spider. It’s springtime in Israel’s Negev Desert, and mom has built a cylinder-shaped web in a bush, with sheets of silk extending from the entrance. This time of year, the hunting is good, as insect populations peak—and inevitably stumble into the spider’s silk sheets. Mother spider grows fat, standing guard over 80 or so eggs, all bundled up in a silk disk, keeping an eye out for infanticidal males, which, like male lions, will kill her young so she’s available to mate again.

But these young ‘uns make it. “The point that she opens the egg sac is the point that she stops feeding,” says Mor Salomon, a biologist at the Israel Cohen Institute for Biological Control. “We have tried giving them food in the lab, but it just doesn’t work—they just don’t feed.”

Feeding time, as a mother spider gives whole new meaning to the term “baby-faced.”

It isn’t that she’s just not very hungry, though: Her intestines already have begun dissolving. By the time the eggs hatch, she already has a meal for her young, in the form of a thin, clear liquid dribbling out of her mouth. They gather around and lap it up for two weeks, and indeed, they’re absolutely dependent on her for food, as their mouthparts aren’t yet developed enough to take on prey. The dissolving of their mother’s intestines intensifies, and toward the end her other organs, save for the heart (which she kinda needs, thank you very much), go as well, until most of her abdomen is filled with sludge.

That is, unless something goes wrong with her young within the first five days. Should they fall victim to an infanticidal male spider, she can actually shut down the dissolving. And with her ovaries still intact, she can mate with him and start the process anew.

But if her young make it those two weeks, she’ll have digested and regurgitated herself to death, losing 41 percent of her body mass. She leaves them with one last gift, though: the rest of her. They clamber over her abdomen and pierce it and suck out the remaining fluid, gorging themselves. “So when they finish her,” Salomon says, “you can see they are very tiny, tiny heads on this very big balloon of an abdomen swollen from all the food they took from her.”

Their mother, on the other hand, isn’t looking so well after losing an additional 54 percent of her body mass, bringing the grand total loss of flesh to 95 percent. “When they finish her, you can see only a hollow exoskeleton,” says Salomon. “You see the abdomen is shrunken, like a balloon whose air came out.”

A dead mother. Notice her abdomen at bottom, shrunken like a deflated balloon. I’m even ruining balloons now, aren’t I.

It’s grotesque, but it’s a brilliant adaptation in the harsh desert. Sure, insects may typically be more abundant in the spring than other seasons, but their numbers still can be unpredictable, given changes in rainfall and temperature. Instead of setting her young loose in a world that isn’t swarming with bugs, she stuffs her face while she can, then gifts her young with dissolved intestines to give them a head start. She’s actually converting that abundant food into tissue and storing it like a refrigerator … that leaks liquified guts instead of freon.

Now motherless, the young stick around for a few weeks to a month, fighting among themselves for insects that get caught in the silk. Unable to compete, the smaller siblings must find other means of feeding. “So what happens is that the small spiderlings leave first; they disperse from the female’s nest,” Salomon says. “And each one sits on a different branch or a different bush and starts its solitary life, making its own nest and web.” For the females among them, life will be short: They mate the next spring and consequently dissolve themselves.

If you see this in the Negev Desert in the springtime, something very weird is about to happen.

This all seems rather short-sighted—committing suicide and all that. But any organism’s overriding drive is to reproduce, sometimes at whatever cost. These devoted mother spiders may perish, but not before giving their kids a huge advantage as they head out into a world where feeding isn’t always a given. Thus mom’s genes carry on to the next generation.

It gets rather more intriguing when you consider that there’s a related species of spider, called Stegodyphus dumicola, that forms into social groups—quite the rarity for arachnids, which typically are lone guns. Only about half the females in this group will feed enough to mature into breeding adults; the other half plays an interesting role. When the group’s eggs hatch, not only will the moms dissolve and regurgitate their insides, but their immature sisters will do so as well, giving up their lives for their nieces and nephews.

If it doesn’t seem to make sense for a mother to kill herself for her young, it would seem to make even less sense for her sisters to sacrifice themselves when the brats aren’t even theirs. But behaviors don’t evolve to the detriment of a species (well, maybe except Juggalo culture—could have gone without that one). It turns out that this actually makes good evolutionary sense. It’s known as kin selection: By helping guarantee their nieces and nephews survive, the sisters are indeed helping pass some of their genes along.

Sure, not as many of those genes if they’d given birth themselves, but still, it’s better than passing along none at all. The same principle goes for other cooperative species like bees and ants. Evolution should drive species to be selfish in the pursuit of siring the next generation, but in fact banding together can be a good evolutionary strategy in its own right.

Read more at Wired Science