Spider Egg Sac Identification: Shapes, Colours, Sizes

A spider egg sac is a small ball, disc or teardrop of silk, usually found in or right next to a web or a spider's silk retreat, or carried by the female herself. The surface can be papery, fluffy or woolly, and the colour ranges from white and cream to tan, yellow, green or pink depending on the species. If you see a spider sitting on it, guarding it or holding it, that confirms it.

Three things are often confused with egg sacs:

• A clothes moth larva's case. The casemaking clothes moth larva carries a silken case that takes on the colour of the fabric it eats (UC IPM). It moves, and it is found on wool or other animal fibres, not in a web.
• Pantry moth webbing. Indianmeal moth larvae leave silken threads and webbing in food packages (UC IPM).
• A spider's silk retreat. Brown recluse spiders build white, frizzy retreats; the actual sacs are the raised, pillow-like shapes inside the fuzz (Spider Mentor).

• Black widow: about 1/2 inch long and 1/2 inch wide, creamy yellow to light tan, opaque, mostly spherical, with a tough, papery surface (UC IPM spiders page); UC IPM's widow spider note describes it as teardrop-shaped, tapered at the top and bulbous at the bottom. About 300 eggs per sac, and more than 10 sacs without mating again (UC IPM).
• Brown widow: about 130 eggs per sac and covered in silk bumps that look like pollen grains (UC IPM); often several sacs hang in the web near the mother (Spider Mentor).
• Brown recluse: off-white silk sacs about 1/3 inch across holding 40 to 50 eggs, up to 5 sacs in a female's lifetime, made inside her irregular retreat (University of Kentucky).
• Black-and-yellow garden spider: papery and tan, a little smaller than a ping-pong ball, over 1,000 eggs each, about 4 per female, attached to plants near the web from about mid-September (Missouri Department of Conservation).
• American house spider: tan, papery sacs in the web; Catchmaster, a pest-product company, gives 100 to 400 eggs per sac.
• Cellar spider (daddy longlegs spider): a loose cluster of eggs held in the mother's jaws (Spider Mentor); Catchmaster gives 25 to 60 eggs.
• Wolf spider: a pea-sized sac attached to the spinnerets at the rear of the mother's abdomen (Missouri Department of Conservation).
• Nursery web and fishing spiders: usually off-white, often with dirt and debris stuck to it, as large as an inch across; carried in the fangs, then fastened to plants inside a nursery web (Spider Mentor).
• Hobo spider: round white or cream silk balls, papery or fluffy, in the web (Catchmaster).
• Spiny-backed orb weaver: a green silk sac (Spider Mentor).
• Trashline orb weaver: several sacs in a vertical line mixed with prey remains and debris, where the mother also hides (Spider Mentor).
• Pirate spider: a reddish, woolly sac a few millimetres wide, hung on its own (Spider Mentor).
• Phrurotimpus (a small ground spider): flat, papery pink to red discs stuck to stones, guarded by the mother (Spider Mentor).

• A ball at the rear end of a running spider: a wolf spider. The female attaches her pea-sized sac to her spinnerets and carries it everywhere; after hatching, the spiderlings ride on her back for up to two weeks or more (Missouri Department of Conservation). The same source notes she may act aggressively while carrying it and searches frantically if separated from it.
• Eggs held in the jaws of a thin, long-legged spider in a messy web: a cellar spider (Spider Mentor).
• A large white ball held under a big brown spider near water or vegetation: a nursery web or fishing spider, which carries its sac in its fangs before building a nursery web (Spider Mentor).
• A spider sitting beside several sacs in a web: widows keep their sacs in the web near them (Spider Mentor).

It depends on the species, from a few dozen to over a thousand eggs per sac:

• Brown recluse: 40 to 50 (University of Kentucky).
• Brown widow: about 130 (UC IPM).
• Black widow: about 300 (UC IPM).
• Black-and-yellow garden spider: over 1,000 (Missouri Department of Conservation).

Not every egg becomes a spider that survives: the Missouri Department of Conservation notes birds such as titmice and chickadees eat garden spider egg cases in winter, and spiderlings of many orb weavers disperse by ballooning on silk threads soon after hatching, sometimes landing miles away (Wegner, BASF spider guide).

• Outdoors, leave it. UC IPM notes that spiders are mostly beneficial because they eat pest insects.
• Indoors, vacuum it. UC IPM says vacuuming works because spiders' soft bodies usually do not survive the trip through the hose, and recommends regular vacuuming or sweeping of window frames, room corners, storage areas and basements. Empty the bag or canister outdoors.
• Stop the next one. Seal cracks in the foundation and gaps around windows and doors (UC IPM).
• Widow or recluse sacs: use the vacuum rather than your hands, and look for the spider nearby. If anyone is bitten and feels unwell, or the bite gets worse, see a doctor. See black widow bites and brown recluse bites.

Research and drafting for this page used AI assistance. Every figure, date and quotation was then checked line by line against the sources listed at the bottom of the page, each of which was opened while writing. Egg counts from Catchmaster, a pest-control product company, are labelled as such; figures from university and state agencies are used wherever they exist. Nothing here is medical advice: after any spider bite with symptoms that worry you, get medical care.