The question of whether baby spiders consume their mother is one of the most unsettling inquiries in animal behavior, yet the answer, for a small number of species, is a profound yes. Spiders exhibit some of the most complex and intense forms of parental care. While most spider mothers simply guard their egg sacs, a few lineages have evolved a strategy where the ultimate act of maternal devotion is the complete self-sacrifice of the mother. This programmed, extreme form of care ensures the maximum survival and fitness of her entire brood, meaning her life ends as her offspring’s first and most nutritious meal.
Defining Matriphagy
The phenomenon of offspring consuming their biological mother is known as matriphagy, translating literally to “mother-eating.” This behavior is not random cannibalism but a highly specialized, terminal reproductive strategy observed in some insects, arachnids, and amphibians. Matriphagy represents a mother’s final investment, converting her body into a high-value nutrient source for her progeny. This mechanism is activated only after the young have hatched, signaling the end of the mother’s reproductive cycle.
The process is generally highly regulated and occurs within the first few weeks after the spiderlings emerge from the egg sac. Rather than a struggle, the mother often facilitates the consumption, indicating that this is a predictable and genetically driven form of programmed death. This self-sacrifice is common within the Eresidae family, known as the velvet spiders, and also occurs in several species of the cobweb spiders (Theridiidae).
Case Studies of Maternal Sacrifice
Liquefaction and Regurgitation
One of the most well-documented examples of matriphagy occurs in the desert spider, Stegodyphus lineatus. The female’s midgut tissues begin to slowly degrade during the incubation period of her eggs, effectively liquefying her internal organs. After the spiderlings hatch, the mother assists by regurgitating nutrient-rich fluids. Within one to two weeks, the young begin to consume her body directly. The spiderlings suck the liquefied tissues primarily from the dorsal side of her abdomen, a process that continues until nearly 96% of the mother’s body mass has been transferred to her offspring.
Trophic Eggs and Solicitation
A different mechanism is seen in the black lace-weaver spider, Amaurobius ferox. The mother initially lays unfertilized trophic eggs for her offspring to consume after they hatch. Once the young have completed their first molt, the mother actively solicits their approach by vibrating her web in a distinct pattern. The spiderlings then descend upon her and consume her body. This consumption is often rapid, with the entire process completed in just a few hours. In the crab spider Australomisidia ergandros, the mother also invests in trophic eggs, but the young consume her body more gradually by sucking hemolymph from her leg joints over a period of weeks.
The Evolutionary Advantage of Being Eaten
The evolutionary rationale for matriphagy is rooted in the concept of terminal investment, where the mother maximizes her reproductive success by dedicating her entire remaining energy and resources to a single, large brood. By offering herself as a meal, the mother converts her body into a concentrated source of protein and fat that is immediately available to her young. This substantial nutrient boost dramatically increases the fitness of the spiderlings.
Offspring that engage in matriphagy exhibit significantly higher weights and a larger body mass when they eventually disperse. This improved size allows for shorter and earlier molting times, which reduces the period the vulnerable young must spend in the nest. Furthermore, the consumption of the mother is linked to a much higher overall survival rate for the brood compared to young deprived of this final meal. These larger, better-nourished spiderlings are also more successful at capturing larger prey items, which further enhances their survival. Matriphagy is therefore a favored strategy in environments where food is scarce or where the initial size and strength of the juveniles are paramount for establishing themselves.
Common Forms of Spider Maternal Care
While matriphagy captures attention for its extreme nature, it is a rare and highly specialized adaptation among the over 50,000 known spider species. The vast majority of spider mothers employ less dramatic, but still dedicated, forms of parental care. The most common behavior is the creation and protection of a silk egg sac, which maintains a constant humidity and shields the developing eggs from predators and parasites. Many species extend their care beyond the egg stage:
- Mothers create and protect a silk egg sac, which shields the developing eggs from predators and parasites.
- Wolf spider mothers carry their egg sac attached to their spinnerets. After hatching, the spiderlings climb onto their mother’s back and ride along until they are ready to disperse.
- Nursery web spiders carry their egg sac in their jaws before spinning a silken nursery web where the young can safely reside during their first few molts.
- Certain jumping spiders provision their offspring with a nutritious, milk-like fluid.
Dedicated, hands-on parenting is a widespread strategy, with matriphagy being its most intense expression.