Spiders are a diverse group of arthropods. Their reproduction, differing significantly from mammals, involves a complex process of producing and managing offspring. Understanding these stages helps identify a female spider preparing to lay eggs.
Physical Changes in the Spider
A primary indicator that a female spider is carrying eggs is a noticeable change in her abdomen. This body segment becomes enlarged, distended, or spherical as eggs mature internally. The abdomen appears taut and uniformly swollen, distinguishing it from a spider that has merely consumed a large meal, which often appears less uniformly distended.
While “pregnant” is a common term, spiders are oviparous, laying eggs that develop outside the mother’s body. Eggs are fertilized internally before being laid and encased in a protective silk structure. This internal development causes the female’s body to visibly expand, preparing her for egg-laying.
Identifying the Egg Sac
The most definitive external sign of a reproductive female spider is the presence of an egg sac. These silk structures vary considerably in appearance depending on the spider species. Egg sacs can be round, disk-shaped, pear-shaped, or spiky, and their colors range from white, cream, or pale yellow to brown, or camouflaged. The texture of these sacs can also differ, appearing silky, papery, tough, or fuzzy.
Female spiders employ various methods for managing their egg sacs. Some species, like wolf spiders, carry their spherical egg sacs attached to their spinnerets at the rear of their abdomen, moving with them constantly. Cellar spiders, in contrast, often carry their loosely wrapped eggs directly in their jaws. Other spiders, such as orb weavers, suspend their egg sacs within their webs, while huntsman spiders might place them under bark or in concealed locations. The number of eggs within a single sac can range from a few dozen to hundreds, and some species can produce multiple sacs throughout their lifetime.
Common Locations and Behaviors
Observing a spider’s habitat and actions provides clues about its reproductive state. Female spiders carrying eggs or guarding egg sacs often seek out sheltered, undisturbed locations. These spots include quiet corners of rooms, under eaves, within dense vegetation, or inside their specific web structures. Outdoors, they are found under rocks, logs, or in leaf litter, protected from predators and environmental elements.
During this period, females may exhibit behavioral changes such as increased reclusiveness, spending more time near their chosen nesting site. They often reduce their movement away from the egg sac and may become more defensive, actively guarding the sac against potential threats. This protective behavior ensures the safety of the developing eggs until the spiderlings are ready to emerge.