What’s for dinner? Mom.
The moms of one spider species give new meaning to the idea of “self-serving.” They feed themselves to their children.
The little cannibals get their start in life in a snug nest added to webs spun by their mom. The webs are a bit like ping-pong nets, explains Mor Salomon. She works at the Israel Cohen Institute for Biological Control in Yehud-Monosson, Israel. Salomon finds the webs of these spiders (Stegodyphus lineatus) in shrubs along dry riverbeds in the Negev Desert in southern Israel. At one end of the web, a female spider spins a small cave. Inside it, she creates what looks like a tiny silk hockey puck holding 70 to 80 yellowish eggs.
Newly hatched spiderlings are trapped in the puck. Mom spider soon pierces the protective silk to free them. From them on, she never eats again. Her children, however, enjoy a gruesome feast.
For two weeks or so, Mom feeds her dozens of young by regurgitating a transparent liquid. Think of it as the soup course. This slurry mixes what’s left of her last meals plus some of her own guts.
Preparation for this part of the meal starts early. The mother’s midgut begins to break down while she is still guarding her eggs. And by the time the pale youngsters hatch, liquefied gut — suitable for baby mouthparts — is building up in her abdomen.
As the liquid spills onto Mom’s face, the spiderlings swarm over her head. The babies form what looks like a face mask made of caramel-colored beads. Each female spider hatches only one brood in her lifetime. It’s easy to understand why. Mom will regurgitate 41 percent of her body mass to feed her babies.
Those spiderlings don’t stop there, either. Mom spider may even invite her offspring to gorge themselves. “She makes no attempt to escape,” Salomon says. Eventually, the spiderlings pierce her abdomen with their mouthparts. The main dish is served. Over the course of several hours, the young drain her innards.
At the beginning of the feeding, Salomon says, “if you touch a leg, she will pull it back. She’s definitely alive.” By the end, the mother spider is clearly dead. All that is left is 4 percent of her original body mass.
The liquefaction process that makes this possible proceeds in an orderly way. Organs that are no longer needed dissolve. Among the organs that remain until the very end: mom’s heart.
Salomon and her colleagues report their findings in the April Journal of Arachnology. (Arachnology is the study of spiders and related animals.)
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arachnid A group of invertebrate animals that includes spiders, scorpions, mites and ticks. Many have silk or poison glands. Arachnology is the study of these animals.
brood A family of animals produced at one hatching or birth. Also, a group of related animals that emerges in a specific region in the same year. Depending on the animal type, the collective group is sometimes also known as a year class.
cannibal A person or animal that eats members of its own species.
gut Colloquial term for an organism’s stomach and/or intestines. It is where food is broken down and absorbed for use by the rest of the body.
Homo A genus of species that includes modern humans (Homo sapiens). All had large brains and used tools. This genus is believed to have first evolved in Africa and over time its members continued to evolve and radiate throughout the rest of the world.
innards Slang term for internal organs, such as the stomach and intestines.
liquefaction The process of turning a solid into a liquid, often through some chemical process.
mass A number that shows how much an object resists speeding up and slowing down — basically a measure of how much matter that object is made from.
organ (in biology) Various parts of an organism that perform one or more particular functions. For instance, an ovary is an organ that makes eggs, the brain is an organ that interprets nerve signals and a plant’s roots are organs that take in nutrients and moisture.
regurgitate To bring up something from the stomach that had been swallowed but not fully digested.
shrub A perennial plant that grows in a generally low, bushy form.
silk A fine, strong, soft fiber spun by a range of animals, such as silkworms and many other caterpillars, weaver ants, caddis flies and — the real artists — spiders.
spiderling An immature spider.
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S. Ornes. “Quieter vibes for city spiders.” Science News for Students. March 25, 2014.
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Original Journal Source: M. Salomon et al. “Dramatic histological changes preceding suicidal maternal care in the subsocial spider Stegodyphus lineatus (Araneae: Eresidae).” Journal of Arachnology. Vol. 43, April 2015, p. 77. doi: 10.1636/B14-15.1.