A spider egg sac is a specialized silk structure created by a female spider to protect her developing offspring. While they are rarely rock-hard, most egg sacs are designed to be extremely durable, exhibiting a texture that is often described as leathery, parchment-like, or tough. This unique toughness comes from the specialized silk proteins used in its construction, which are engineered for maximum defense against the environment and predators.
The Structure and Composition of the Egg Sac
The protective qualities of the egg sac are due to the advanced biological engineering of the silk used to construct it. Spiders use specialized silk glands, known as tubuliform glands, to produce the main constituent of the sac, called tubuliform silk. This silk has a protein composition distinct from the dragline silk used for webs, featuring a high content of the amino acid serine, which contributes to its unique mechanical properties.
The sac is typically a multi-layered structure. The dense, tightly woven outer layer provides mechanical strength and defense against moisture, giving the sac its characteristic firm or papery texture. Inside this tough exterior, the spider spins a looser, fluffier layer of silk that acts as insulation and cushioning for the eggs. This internal structure helps to maintain a consistent humidity level and temperature, shielding the delicate contents from threats such as parasitic wasps and ants.
Types of Spider Egg Sacs and Their Appearance
The final appearance and texture of an egg sac vary dramatically depending on the species that created it. Some spiders, like the black widow, produce sacs that are smooth and spherical, with a very tight weave that feels firm and durable, almost like a small, tough ball. These types of sacs are often suspended by silken threads in the spider’s web, requiring a rigid structure to maintain their shape.
In contrast, certain house spiders create sacs that are much less defined, often appearing as a loose, fluffy mass of silk hidden within the existing web. This type has a softer, almost cotton-like texture, relying on concealment rather than outright physical toughness for protection. A third distinct type is the carried sac, exemplified by the wolf spider, which attaches a tough, pearl-like sac directly to its spinnerets and physically drags it around. The silk in these carried sacs must be exceptionally durable to withstand constant abrasion and movement.
What Happens Inside the Egg Sac
The protective silk cocoon encloses the actual spider eggs, which are soft, small, and highly vulnerable. A female may lay anywhere from a few dozen to several hundred eggs within a single sac, depending on the species. The eggs are often glued together by a glutinous substance, and they undergo incubation within the safety of the silk chamber.
Once the eggs hatch, the tiny spiderlings remain inside the sac until they complete their first molt, living off the remnants of their yolk sac. They stay protected until they are slightly more developed. To exit the sac, the spiderlings collectively chew a small, neat hole in the tough silk wall, using their tiny fangs to breach the protective layers before they disperse into the environment.
Safe Removal and Disposal
When an egg sac is discovered, its tough construction is a primary consideration for removal. Due to the density of the silk, simply crushing the sac is often ineffective and can lead to the immediate and widespread dispersal of hundreds of tiny spiderlings. This is especially true for the more rigid, tightly woven sacs.
The safest and most recommended method for removal is using a vacuum cleaner with a hose attachment to suction the entire sac intact. The vacuum bag or canister contents must be immediately sealed and disposed of in an outdoor trash bin. Preferably, the contents are frozen for a minimum of 24 hours to ensure the spiderlings do not survive. Alternatively, an aerosol pesticide spray specifically designed for spiders can be used to thoroughly coat the sac, which will penetrate the silk and kill the contents before removal.