The Black Widow spider, a member of the genus Latrodectus, is known for its potent venom and its dark, glossy appearance marked by the distinctive red hourglass shape on the female’s abdomen. This reputation often includes the claim that the female preys upon her own young. The mother Black Widow’s behavior toward her offspring is more nuanced than simply devouring them, and she does not typically consume her babies.
The Specifics of Filial Cannibalism
The notion of filial cannibalism, where a parent consumes its progeny, is not standard maternal behavior for the female Black Widow. Once the eggs hatch and the spiderlings emerge from the protective silken sac, the mother does not pursue them as food. Her primary role is the defense of the egg sac, which she guards until the young are ready to leave.
A mother Black Widow may accidentally consume an unviable egg or a stillborn spiderling remaining within the egg sac. This is considered resource management, not deliberate predation on healthy young. The mother focuses on catching prey to maintain her body condition, which is necessary for producing subsequent egg sacs.
What Happens When Black Widow Spiderlings Hatch
The high mortality rate of young Black Widows often fuels the misconception that the mother eats her offspring. A single female can produce several egg sacs throughout a season, each containing hundreds of eggs. Only a small fraction of these young spiders survive their first few weeks due to intense competition and a lack of resources.
A more common behavior is sibling cannibalism, where the newly hatched spiderlings consume one another inside the egg sac or shortly after emergence. The larger spiderlings gain a survival advantage by preying on their smaller siblings, acquiring necessary nutrients for growth. After one to three weeks, the surviving spiderlings leave the mother’s web through a process called ballooning, spinning silk threads that catch the wind to carry them to new locations.
Sexual Cannibalism: The More Common Behavior
The Black Widow’s reputation for cannibalism originates from the practice of sexual cannibalism, not from eating her young. This behavior involves the female consuming the male spider, typically during or immediately after copulation. This act is why the genus earned the name “widow” spiders.
The female gains a substantial nutritional boost from this calorie-rich meal, which she allocates toward the development and provisioning of her eggs. For the male, this sacrifice can increase the chances of his paternity, as the female may be less likely to mate again or his sperm may be retained longer. This behavior, though not universal, is the source of the spider’s perception as a cannibal.