The black widow spider, recognized by its glossy black body and the distinct red hourglass marking on its underside, has long captured human attention. This spider’s reputation often precedes it, primarily due to the potent venom produced by the female. Understanding the life cycle of this arachnid, particularly its reproductive habits, offers insight into its presence in various environments.
The Reproductive Process
Black widow mating typically occurs in the warmer months, from spring into early summer. The male black widow, significantly smaller than the female, approaches her web cautiously. He performs a “vibratory song and dance” on her web, plucking the silk strands to signal his presence and intent. After this elaborate courtship, the male inserts his palps into the female’s reproductive openings to transfer sperm.
Sexual cannibalism, where the female occasionally consumes the male after mating, contributes to the “widow” in their name. This act provides the female with a protein-rich meal, benefiting her subsequent egg production. Following successful mating, the female prepares to lay her eggs, encasing them in a protective silk sac.
Number of Eggs and Egg Sacs
A single black widow egg sac can contain 25 to over 900 eggs, with averages often cited between 200 and 400. The egg sacs are usually spherical or pear-shaped, with a paper-like texture, and are often white, tan, or gray.
A female black widow can produce multiple egg sacs within a single breeding season. She may create anywhere from four to nine egg sacs during one summer, with some capable of producing more than ten. Factors like the female’s health, food availability, and environmental conditions influence the number of eggs and egg sac frequency. Females can also store sperm after their initial mating, allowing them to produce several subsequent egg sacs without needing to re-mate.
Spiderling Development and Dispersal
Once the eggs are laid and enclosed within the protective sac, they undergo an incubation period. This phase typically lasts two to four weeks, depending on environmental factors like temperature and humidity. The spiderlings hatch inside the sac and usually undergo their first molt before emerging.
Upon emergence, these tiny spiderlings, often pale or yellowish-white, disperse from the egg sac. A common method of dispersal is “ballooning,” where they spin silk threads that catch air currents, allowing them to travel to new locations. Despite the large number of eggs laid, there is a very high mortality rate among young black widows due to factors like cannibalism among siblings, predation, and limited food resources. Only a small fraction of the spiderlings survive to maturity.