Brown recluse egg sacs are small, off-white to tan silken pouches, roughly the size of a dime or smaller, measuring less than one inch (2.5 cm) across. They have a flattened, somewhat irregular shape and a papery or loosely woven silk texture that sets them apart from the tightly woven, perfectly round egg sacs of many other spider species. If you’ve found something in your home and you’re comparing it to pictures online, those details of size, color, and texture are the quickest way to narrow down what you’re looking at.
What a Brown Recluse Egg Sac Looks Like
The egg sac is made of off-white to cream-colored silk with a slightly rough, papery surface. Unlike the smooth, ball-shaped sacs that orb weavers and black widows produce, a brown recluse egg sac looks loosely constructed and somewhat flattened, almost like a small silk pouch pressed against a surface. The silk is not shiny or tightly packed. It has a matte, cottony quality that can pick up dust and debris from its surroundings, sometimes making it look slightly dirty or grayish over time.
Inside each sac are roughly 40 to 50 tiny yellowish eggs. You won’t see the eggs unless the sac is torn open, but if you do spot small yellow spheres inside a broken silk pouch, that’s consistent with a brown recluse sac. The sac itself is typically tucked against a flat surface rather than dangling from a web strand, which is another visual clue that distinguishes it from other species.
Where You’ll Find Them
Brown recluse spiders are true to their name. They prefer dark, dry, undisturbed spaces, and that’s exactly where females attach their egg sacs. Indoors, the most common spots are inside storage boxes, wall voids, crawl spaces, closets, and drawers that don’t get opened often. Shoes left in a garage, coats hanging in a back closet, and piles of stored clothing are all prime locations.
Outdoors, egg sacs turn up under woodpiles, beneath tree bark, in rock piles, under overhangs, and in leaf litter. The female builds a flat, sheet-like silk retreat and incorporates the egg sac into it, so you may notice a small web-like mat of silk in the area around the sac rather than a traditional web structure. If you’re cleaning out a shed, basement, or attic and find a small silk pouch pressed flat against cardboard or wood, that’s the typical presentation.
How Many Egg Sacs One Spider Produces
A single female brown recluse can produce two to five egg sacs per season, with two or three being most common. Each sac holds 20 to 50 eggs, meaning one spider can produce 150 or more spiderlings in a single year. Making matters worse, a female only needs to mate once in her lifetime to continue producing fertile eggs. This is why infestations can grow quickly in homes that provide the dark, undisturbed conditions these spiders prefer. Finding one egg sac usually means there are more nearby.
How to Distinguish Them From Other Spider Egg Sacs
Several common household spiders produce egg sacs that can be confused with brown recluse sacs. Here’s how to tell them apart:
- Black widow egg sacs are round, smooth, and cream to tan colored, with a tighter, more polished silk surface. They’re usually suspended in messy cobwebs rather than pressed flat against a surface.
- Cellar spider egg sacs are loosely held clusters of eggs wrapped in a thin, nearly transparent layer of silk. The mother often carries the sac in her jaws rather than attaching it to a surface.
- Wolf spider egg sacs are round and dense, and the female carries the sac attached to her spinnerets, dragging it behind her. You won’t find these tucked into a box.
The brown recluse sac’s flattened shape, papery texture, and placement in a silk retreat against a flat surface in a dark location are the combination of features to look for.
Confirming the Spider Nearby
If you find a suspicious egg sac and want to confirm it belongs to a brown recluse, look for the adult spider in the immediate area. Brown recluse adults are light brown with a darker violin-shaped marking on the back, just behind the eyes. That fiddle mark is the most well-known identifier, but it develops as the spider matures and may not be visible on younger spiders.
A more reliable feature is the eyes. Most spiders have eight eyes, but the brown recluse has only six, arranged in three pairs. You’ll need a magnifying glass or a close-up photo to see this, but it’s the single most definitive trait. The legs are also distinctive: uniformly colored, slender, and completely smooth, without the banding or spines common on many look-alike species like grass spiders or hobo spiders.
Females tend to stay close to their egg sacs within their silk retreat, so if you’ve found a sac, checking the immediate surroundings with a flashlight will often reveal the spider nearby.
What to Do If You Find One
Destroying a single egg sac is straightforward. You can crush it, vacuum it up, or seal it in a bag and dispose of it. The real concern is what the sac represents: an established spider population in that area. Because each female produces multiple sacs per season and the spiders are nocturnal and reclusive, the ones you see are a fraction of those present.
Reducing clutter, sealing cracks and gaps around baseboards and door frames, and moving storage boxes off the floor and away from walls all limit the sheltered spaces these spiders need. Sticky traps placed along walls and in closets are effective both for monitoring how many spiders are present and for reducing their numbers over time. For significant infestations, a pest control professional familiar with brown recluse behavior can treat wall voids and other harborage areas that are difficult to reach on your own.