Spiders undergo a unique reproductive process. When a spider is described as “pregnant,” the more accurate biological term is “gravid,” meaning she is carrying developing eggs internally or has recently deposited them within a protective silk structure. Spiders do not give live birth; instead, they lay eggs, which are then typically housed in an egg sac. This egg-laying strategy is a fundamental aspect of their life cycle, ensuring the protection and development of their offspring before they emerge as spiderlings.
Physical Indicators of a Gravid Spider
Observing physical changes in a spider can often provide the first clues that she is gravid. An enlarged abdomen is a primary indicator, often appearing rounder or more pear-shaped than usual. This expansion occurs as the spider’s body accommodates developing eggs, making the abdomen disproportionately large compared to her cephalothorax, the fused head and thorax. Some species may also exhibit subtle changes in the color or texture of their abdomen as they near egg-laying. For certain spiders, such as wolf spiders, the female’s palps can become stouter and hairier when she is carrying eggs.
Behavioral Clues
Changes in a spider’s behavior can also signal that she is gravid. Female spiders carrying eggs often display reduced activity levels, moving more slowly and less frequently, linked to preparing for egg deposition and caring for young. Gravid spiders tend to spend more time in secluded or hidden locations, seeking undisturbed areas to lay their eggs and building a protective silk retreat for the impending egg sac. Some species may also exhibit increased territoriality or aggression as they become more protective of their chosen egg-laying site and potential offspring. Additionally, a gravid spider might show altered feeding habits, potentially exhibiting a decreased appetite or even refusing food as she approaches egg sac production.
The Presence of an Egg Sac
The most definitive sign is the presence of an egg sac. These sacs, meticulously crafted from silk, vary widely in appearance depending on the spider species.
- Appearance: Spherical, round, oval, pear-shaped, disc-shaped, spiky, or teardrop-shaped.
- Size: Typically proportional to the spider, often smaller than a quarter, containing dozens to thousands of eggs.
- Color: Commonly white, cream, off-white, beige, tan, brown, yellow, green, or russet.
- Texture: Papery, silken, fluffy, smooth, rough, or bumpy.
Spider egg sacs are found in diverse locations, either attached to webs, hidden in crevices, under leaves, or within burrows. Some species, like wolf spiders, actively carry their egg sacs attached to their spinnerets, while daddy-long-legs spiders transport them within their jaws. Other spiders may abandon their egg sacs after creation, relying on the sac’s protective qualities, while many species will guard them diligently until the spiderlings emerge.
What Happens After Egg Laying
After laying her eggs, the female spider’s role often shifts to guarding or carrying the silk egg sac. This maternal care continues until the eggs hatch, a period that varies significantly by species and environmental conditions, typically ranging from a few weeks to several months. Some spider species even have eggs that will overwinter within the protective sac, emerging in the spring.
Hatching and Emergence
Once the eggs hatch, the immature spiders, known as spiderlings, emerge, resembling miniature versions of their adult counterparts. They often remain inside the egg sac for a period, sometimes undergoing their first molt before venturing out. When ready to emerge, spiderlings may use their tiny fangs to cut a hole in the silk sac.
Dispersal
Spiderlings soon begin to disperse, either by walking or by a process called “ballooning,” where they release silk threads to catch air currents, carrying them to new locations. For instance, wolf spiderlings will climb onto their mother’s back, remaining there for about ten days before dispersing. The mother spider may continue to protect her offspring for a short time after their emergence.