If you’ve found a round, spiky egg sac that looks like a tiny sea urchin or a World War II naval mine, you’re almost certainly looking at the egg sac of a brown widow spider. The brown widow is the only common spider that produces these distinctive spiked silk spheres, and spotting one is actually the easiest way to confirm you have brown widows around your home.
What the Egg Sac Looks Like
A brown widow egg sac is roughly marble-sized, pale yellow, and covered in dozens of small silk spikes projecting from the surface. The University of California, Riverside describes it as resembling “a big pollen grain or one of those harbor mines from World War II.” No other widow species makes anything like it. Black widow egg sacs, by comparison, are yellow and smooth, sometimes with a slight point at the top. If the sac has spikes, it belongs to a brown widow.
The eggs inside are spherical, each about 1 millimeter across. Research published in the Journal of the Royal Society Interface found the eggs are coated with a dense layer of tiny granules that help protect them from bacterial infection. Those outer silk spikes serve a similar protective role, making the sac harder for parasites and predators to access.
How to Identify the Spider Itself
Brown widows are relatives of black widows, but they’re smaller and less dramatically colored. Their bodies range from tan to dark brown, sometimes with mottled or striped leg patterns. The key identifying feature is on the underside of the abdomen: an hourglass marking that is orange to yellow-orange, not the bright red hourglass of a black widow.
The spider itself can be hard to spot since brown widows are shy and mostly active at night. That’s why the spiky egg sac is often the first and most reliable clue. A single female can produce multiple egg sacs over her lifetime, so finding one usually means more are nearby.
Where Brown Widows Build Their Nests
Brown widows strongly prefer sheltered, semi-hidden spots around the outside of buildings. You’ll find their webs and egg sacs tucked under patio furniture, inside the lips of flower pots, beneath eaves, along fence rails, inside mailboxes, and under outdoor storage bins. They tend to stay close to human structures rather than out in open yards or natural habitats.
In some areas along the Gulf Coast, infestations have been severe enough that researchers documented literally hundreds of brown widows around the exterior of a single building. They also turn up inside garages, sheds, and other spaces that aren’t frequently disturbed.
Where Brown Widows Are Found
Brown widows have spread dramatically across the southern United States and continue to expand their range. They were first established in peninsular Florida in the early 1900s and are now found in every Florida county. Established populations have been confirmed in Georgia (including Atlanta and Athens), South Carolina, Texas, Mississippi, Louisiana, and southern California, along with Hawaii.
Globally, they’re common across much of Africa, along the eastern coast of South America (especially Brazil), and have been introduced to Australia, Papua New Guinea, Indonesia, and Japan. If you live in a warm or subtropical climate, brown widows are a reasonable possibility whenever you encounter a spiky egg sac.
Are Brown Widows Dangerous?
Brown widows are significantly less dangerous than black widows, despite being close relatives. Drop for drop, their venom contains similar toxins, but a brown widow either produces far less venom or can’t inject as much during a bite. A study of 15 verified brown widow bites in Africa found that none of the victims developed the classic symptoms associated with widow spider envenomation.
The typical brown widow bite causes pain at the bite site and a red mark, not much different from the bite of an ordinary household spider. That said, rare cases have been more serious. One documented case in central Florida involved moderate symptoms resembling a black widow bite, including significant pain, nausea, and elevated blood pressure. These severe reactions are uncommon.
Interestingly, because brown widows appear to be displacing native black widows in parts of their range, researchers at UC Riverside have suggested that the overall risk of serious spider bites may actually decrease as brown widows spread into areas previously occupied by their more dangerous cousins.
How to Remove Egg Sacs Safely
If you’ve found spiky egg sacs and want to get rid of them, the process is straightforward. Wear gloves (thick gardening gloves work well) and use a stick or tool to knock the egg sacs and webbing loose, then crush or bag them for disposal. The mother spider is likely hiding nearby, so check the surrounding area carefully before reaching into tight spaces.
Reducing clutter around the outside of your home removes the sheltered spots brown widows prefer. Regularly sweeping under eaves, behind shutters, and around outdoor furniture disrupts their webs and discourages them from settling in. Since brown widows strongly favor the exterior of buildings, focusing your cleanup efforts outside is more productive than treating indoor spaces.