Spiders exhibit many remarkable behaviors, and a common question is whether they consume others of their own kind. This phenomenon, known as cannibalism, reveals complex interactions and survival strategies within arachnid ecology.
The Reality of Spider Cannibalism
Spiders do consume other spiders, a phenomenon known as cannibalism. This behavior occurs across many species, though it is not universal. It involves one spider preying on another of the same species for food. This can occur between individuals of different sexes, sizes, or developmental stages. It is a significant aspect of spider biology, influencing population dynamics and individual survival.
Driving Factors Behind the Behavior
Hunger and Territoriality
Several factors motivate cannibalistic behavior among spiders, often linked to survival and reproduction. Hunger is a primary driver; when food sources are scarce, spiders may resort to consuming conspecifics for nutrients. This is particularly true for wolf spiders, where limited prey can lead to them preying on each other. Territorial disputes can also escalate to cannibalism, as spiders defend their space and resources from rivals. Studies on wolf spiders, like the Mediterranean tarantula, show that territorial encounters can result in one spider consuming the other, especially when individuals are similar in size.
Size Differences
Size differences also play a significant role, with larger spiders often preying on smaller ones. This is evident in many species, where a substantial size disparity makes smaller individuals vulnerable.
Sexual Cannibalism
Sexual cannibalism, where one partner consumes the other during or after mating, is another motivation. This behavior, most commonly observed with females eating males, can provide the female with vital nutrients for egg production, increasing the survival chances of her offspring. In some cases, the male’s self-sacrifice during mating can even increase his paternity success.
Variations and Exceptions
Sexual Cannibalism Examples
Cannibalism manifests in diverse ways across different spider species, with some notable exceptions. The Australian redback spider, a black widow relative, offers an example of sexual cannibalism where the male actively “somersaults” into the female’s fangs during copulation. This act can prolong mating and increase the male’s paternity. While the black widow spider is famously associated with sexual cannibalism, this behavior is less frequent in many North American species in the wild than commonly believed, often occurring more in captivity or when females are hungry.
Male Cannibalism and Courtship Strategies
Male spiders also exhibit cannibalism in some species. For instance, in Micaria sociabilis, males have been observed consuming females, particularly older ones, which may be an adaptive foraging strategy or a form of mate choice. Nursery web spiders (Pisaurina mira) display a unique courtship where males offer silk-wrapped “nuptial gifts” to females, or even bind the female’s legs with silk, to reduce the risk of being eaten during mating.
Social Spiders and Sibling Cannibalism
Conversely, social spiders live communally, a lifestyle that often reduces or eliminates cannibalistic tendencies within their colonies. Even among juvenile redback spiders, sibling cannibalism can occur shortly after hatching.