Matriphagy is a phenomenon where offspring consume their mother, representing a form of parental investment. This behavior, literally meaning “mother-eating,” is not random cannibalism but a programmed, self-sacrificial biological event. For certain arachnids, a mother willingly becomes a final, nutrient-dense meal for her brood, ensuring their survival and early success. This ultimate sacrifice is an adaptation that has evolved across various species to pass on genes.
Defining Matriphagy in Spiders
Matriphagy in spiders is a precise, biologically orchestrated event where the mother’s body is intentionally converted into a food source for her young. This process differs from simple scavenging because the female facilitates the consumption while often still alive. The mechanism is a form of terminal investment, redirecting the mother’s physiological resources to her offspring’s growth. This preparation often involves the internal disintegration of the mother’s midgut tissue, essentially liquefying her internal organs.
The mother’s body, particularly the abdomen (opisthosoma), becomes laden with high-protein and lipid-rich material. Once the young hatch and reach a specific developmental stage, the mother’s programmed decline begins. In many species, the mother is functionally sterile and has no further reproductive future, making the sacrifice a final investment in her single brood. This process ensures the young receive a meal richer and more readily available than any prey they could catch.
Species That Practice Maternal Sacrifice
The act of maternal sacrifice is found across several spider families, with the process unfolding differently depending on the species. In the African social spider, Stegodyphus dumicola, the mother actively invites her young to consume her. As she becomes sluggish due to internal physiological changes, she shakes the communal web, mimicking a trapped insect. The spiderlings recognize this signal, descend upon her, and begin to feed on her tissues, resulting in a quick end.
A different scenario occurs in the black lace-weaver spider, Amaurobius ferox. After the spiderlings hatch and consume unfertilized food eggs, the mother initiates the final stage of matriphagy through web vibrations and drumming. The spiderlings swarm her, bite her body, and inject a venom that quickly liquefies her internal contents. This rapid, coordinated consumption ensures the young receive their meal within a few hours.
The Australian crab spider, Australomisidia ergandros, offers a more protracted form of sacrifice. The mother is consumed gradually over several weeks as the young slowly suck her hemolymph, or spider blood. This slow consumption, along with the initial provisioning of trophic eggs, meters the mother’s resources out to the offspring over a longer period. Matriphagy has also been observed in multiple species of the Anelosimus genus, demonstrating that this behavior is not limited to a single evolutionary path.
The Evolutionary Payoff of Being Eaten
The act of matriphagy is maintained in the gene pool because it offers significant advantages to the offspring. Consuming the mother provides a high-quality, one-time nutritional boost that translates directly into enhanced fitness. Spiderlings that engage in matriphagy show a substantial increase in body mass, sometimes gaining 2.5 times their initial weight.
This high-protein meal accelerates their development, resulting in shorter and earlier molting times. Larger body size and faster growth allow the young to disperse sooner, reducing vulnerability to predators and resource scarcity. Matriphagous offspring are also more successful at capturing larger prey items compared to non-matriphagous counterparts. This enhanced survival rate ensures the mother’s genetic legacy is passed on with a higher probability than if she had survived to raise a less-provisioned brood.
Beyond Matriphagy: Other Forms of Parental Nutrient Transfer
While consuming the mother is the most extreme form of parental nutrient transfer, spiders employ other methods to provision their young. In many subsocial species, the mother provides food without sacrificing her body, a behavior known as regurgitation feeding. Species within the Stegodyphus genus, for example, initially feed their hatchlings with partially digested food regurgitated from her own gut.
Another strategy is the production of trophic eggs, which are unfertilized eggs laid specifically as a nutrient supplement for the hatchlings. The black lace-weaver spider and the crab spider both employ this tactic before matriphagy commences. Related to matriphagy is gerontophagy, observed in some social spiders like Stegodyphus dumicola, where the young consume non-reproducing, older females (allomothers). These varied behaviors underscore a shared evolutionary drive to maximize the survival and success of the next generation.