Spider egg sacs are protective silk casings where female spiders deposit their eggs. These sacs shield developing spiderlings from environmental factors and predators. People often want to know if a sac is empty, either out of curiosity or concern about emerging spiderlings. Understanding their characteristics provides insight into their contents.
Characteristics of an Occupied Egg Sac
An occupied spider egg sac is typically plump and firm, indicating the presence of eggs or developing spiderlings. Their appearance, shape, and size vary significantly by species. They are commonly spherical, teardrop-shaped, or disc-shaped, usually about the size of the spider that produced them.
Active sacs range in color from white or off-white to cream, brown, or yellowish-green, depending on the species and environment. The silk is tightly woven, forming a resilient, intact outer layer that protects the eggs from external threats.
Distinctive Signs of an Empty Egg Sac
An empty spider egg sac shows several distinct visual and tactile cues. A primary sign is noticeable deflation or shriveling; it will look flattened, collapsed, or caved in, having lost its internal mass.
Small, irregular holes or tears are often present on the surface. These openings are typically created by spiderlings chewing their way out, or sometimes by the mother spider assisting emergence. An empty sac will feel papery, lightweight, or easily compressible, lacking the firmness of a sac containing eggs. It may also appear dirtier or discolored compared to a freshly laid sac. Additionally, there will be no signs of activity, and surrounding web structures might appear less maintained.
What Happens After Spiderlings Emerge
Once spiderlings develop sufficiently, they hatch from their eggs within the sac. They typically chew a small hole in the silk casing to emerge, sometimes aided by a silk-digesting fluid or the mother spider. After emergence, spiderlings often remain clustered, sometimes undergoing their first molt inside or immediately outside the sac.
Young spiders then disperse from the sac’s vicinity. Many species, especially web-spinning spiders, use “ballooning.” This involves spiderlings spinning thin silk strands that catch air currents, carrying them to new locations, sometimes far from their origin. This dispersal leaves behind the empty silk sac.
Dealing with an Egg Sac
Once a spider egg sac is determined to be empty, it can be safely removed without concern for live spiderlings. The easiest method is often using a vacuum cleaner hose attachment to suction the sac. After vacuuming, dispose of the vacuum bag outdoors in a sealed container, or empty the canister outside.
Alternatively, an empty sac can be carefully swept into a sealed bag using a broom, or removed with a tissue or gloved hand. An empty sac poses no threat, as all contents have already departed. If uncertain whether a sac is empty, observe it from a distance or proceed with caution during removal. Most spiders are not harmful to humans, and their empty egg sacs are simply remnants.