Spider reproduction is a unique and intricate process. Spiders employ diverse methods to find a mate, transfer genetic material, and ensure the survival of their offspring. These strategies involve sophisticated behaviors and adaptations, revealing a complex biological world.
The Courting Rituals
Before mating can occur, male spiders must perform elaborate courtship rituals to signal their identity and intentions to a female, avoiding being perceived as prey. These displays vary widely among species, often involving visual, vibrational, or chemical cues. For example, many web-building spiders pluck threads of the female’s web in a distinct rhythm to announce their presence and readiness to mate. Some male wolf spiders, like Hygrolycosa rubrofasciata, drum their legs on surfaces, with faster drumming often indicating a more viable mate.
Visual displays are common in species like jumping spiders, where males exhibit intricate dances and show off specialized ornamentation on their forelegs. Chemical signals, or pheromones, also play a role, with some female web-spinning spiders releasing these substances into the air or coating their webs to attract males. In some instances, males offer “nuptial gifts,” such as a wrapped insect, to distract the female during courtship and reduce the risk of being attacked.
The Mechanics of Mating
Spider mating involves specialized anatomical features and a unique, indirect method of sperm transfer. Unlike many other animals, male spiders do not directly transfer sperm from their testes to the female’s reproductive tract. Instead, the male first deposits a drop of fluid containing sperm onto a small silk structure, often called a “sperm web.”
After depositing the sperm, the male draws it into his pedipalps, which are modified appendages near his head. These pedipalps act as copulatory organs, functioning like syringes to pick up and inject the sperm. When the female is receptive, the male inserts his pedipalps into her epigynum, a hardened plate on the underside of her abdomen that serves as her genital opening. The sperm then moves into storage receptacles, called spermathecae, connected to the oviducts, where fertilization of eggs will later occur.
Post-Mating Dynamics
The period following mating can be hazardous for the male. Sexual cannibalism, where the female consumes the male, is a recognized phenomenon, though its prevalence varies by species. This behavior can provide the female with additional nutrients, supporting the production of healthy egg sacs and increasing offspring survival and size. For instance, studies on dark fishing spiders show that females who cannibalize their mates produce nearly twice as many spiderlings, which are also larger and survive longer.
Male spiders have evolved various strategies to cope with the risk of cannibalism. Some males, like certain orb-weaver species, may quickly detach their pedipalps and flee, or even self-sacrifice by somersaulting into the female’s fangs, which can extend mating time and improve sperm transfer success. In other cases, males may smear a secretion over the female’s epigynum, creating an “epigynal plug” to prevent her from mating with other males, thereby increasing their paternity. After successful mating and sperm storage, the female lays her eggs into a protective silk egg sac, which can contain hundreds or thousands of eggs. She may then guard the sac, attach it to her web, or carry it with her until the spiderlings emerge.
Remarkable Diversity in Spider Mating
The spider world showcases a diverse array of mating strategies. The diving bell spider (Argyroneta aquatica), unique for living almost entirely underwater, mates in its submerged silk bell. The male constructs his own diving bell adjacent to the female’s, then spins a tunnel to break into her bell for copulation. Males of this species are unusually larger than females, which may be beneficial for navigating water resistance and competing for mates.
Another adaptation is male self-sacrifice, observed in species like the Australian redback spider (Latrodectus hasselti) and some Argiope orb-weavers. During mating, the male redback spider somersaults and presents his abdomen to the female’s fangs, allowing himself to be eaten. This act can increase the duration of copulation and improve the male’s paternity share, as high male mortality during mate searching means few males get multiple mating opportunities. In some Argiope species, males may even die spontaneously during copulation, particularly upon the insertion of their second pedipalp, a programmed death that occurs regardless of female aggression.