What’s for dinner? Mom.

Spider’s extreme motherhood ends with fatal family feast

Kids do the darnedest things: Tiny yellow spiderlings (shown close up) crowd over their gray mother. Eventually, the young spiders will eat her.

JORGE ALMEIDA/FLICKR (CC BY-NC-ND 2.0)

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.)

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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