Spiders often spark curiosity due to their unique behaviors, especially concerning their offspring. The question of whether spiders consume their young is a common one. While the idea might seem unsettling, the reality is nuanced, revealing a spectrum of parental strategies driven by survival and environmental pressures, examining instances of filial cannibalism alongside remarkable examples of dedicated maternal care and the eventual journey of spiderlings into independence.
Filial Cannibalism in Spiders
In some instances, spiders do engage in filial cannibalism. This behavior occurs in specific contexts, often driven by environmental factors. One primary reason for this behavior is resource scarcity or stress, where a mother might eat some or all of her offspring to survive periods of extreme food shortage. Consuming offspring in such situations can allow the mother to regain nutrients, potentially enabling her to reproduce again when conditions improve, or to provide sustenance for the remaining spiderlings if resources are critically low.
Another, rarer form of this interaction is matriphagy, where the mother intentionally sacrifices herself to be consumed by her young. For example, in some species like the African social spider (Stegodyphus dumicola) or the black lace-weaver (Amaurobius ferox), the mother may even encourage her offspring to consume her body after they hatch, ensuring their survival and increased body mass. This behavior ensures offspring have a higher survival rate, faster development, and improved hunting skills.
Filial cannibalism can also occur if offspring are weak or unviable. A mother might consume these less robust spiderlings to reabsorb their nutrients, allowing her to invest energy into stronger, more likely-to-survive offspring. Furthermore, cannibalism among spiderlings themselves can occur shortly after hatching, especially before they disperse, helping to reduce competition for food among siblings.
Parental Care Beyond Cannibalism
While filial cannibalism exists in some species, it is far from the norm for most spiders. Many spider species exhibit diverse and often dedicated forms of maternal care. The most common form of care involves the creation and protection of egg sacs. Nearly all female spiders construct a silk egg sac to enclose and safeguard their eggs from predators, parasites, and environmental fluctuations. These sacs vary greatly in shape, color, and texture, often camouflaged or reinforced with multiple layers of silk.
Many mother spiders actively guard their egg sacs, remaining close by to defend them until the spiderlings emerge. Some species take this a step further by carrying their egg sacs with them. For instance, wolf spiders attach their spherical egg sacs to their spinnerets, carrying them wherever they go, while cellar spiders carry their loosely wrapped eggs in their jaws.
Beyond guarding the eggs, some spider mothers extend their care to the hatched spiderlings. Wolf spider mothers, for example, allow hundreds of their newly hatched young to climb onto their backs, carrying them for over a week until they are ready for independence. Other species, like some social spiders, may provision their young with regurgitated food or bring captured prey back to the nest for the spiderlings to consume, ensuring their early nutritional needs are met. Some even maintain elaborate silk nursery webs to protect their developing young.
Spiderling Dispersal and Independence
After hatching and receiving initial maternal care, spiderlings embark on a journey toward independence. They typically remain clustered within or near the egg sac, often undergoing their first molt inside it. Once their cuticles harden, they begin to disperse from the maternal nest to establish their own territories. This dispersal is important to avoid competition for food and to prevent cannibalism among siblings.
One method of dispersal is “ballooning” or “kiting.” Spiderlings, and sometimes larger spiders, climb to a high point, release fine silk threads from their spinnerets, and allow air currents or even electric fields to lift them. This aerial journey can span distances from a few meters to hundreds of kilometers, enabling them to colonize new habitats. Charles Darwin observed spiderlings landing on the rigging of the HMS Beagle far out at sea.
Other dispersal methods include walking or crawling, typically used for shorter distances, especially by ground-dwelling species. Some foliage-dwelling spiders use “bridging,” where they drop on a silk line to swing to adjacent branches. Once dispersed, spiderlings are generally self-sufficient, beginning their lives as independent predators.