How to survive America’s most dangerous spider: They’re spreading across the US – and you often only feel them when a wound opens and your urine turns black. Here they hide in houses… and what to do immediately after a snack

First comes the bite – often so painless that victims don’t even realize it has happened.

Then, within minutes, the poison starts to take effect and the pain begins.

The skin begins to burn and throb, punctuated by electric shocks. When the small blood vessels that nourish the skin are destroyed, first a bruising occurs and then, in more severe cases, an open, festering wound.

Within a week or two, a hardened black ulcer may form over the dead tissue, eventually falling away as the wound begins to heal.

But in rare cases, damage can occur doesn’t stop at the skin. The poison attacks red blood cells, turning the urine Coca-Cola-colored and, in the most severe cases, causing kidney failure and even death.

This is what it can be like to be bitten by a brown recluse – one of America’s most dangerous spiders.

And unlike America’s other notoriously dangerous spider, the black widow – instantly recognizable by its shiny black body and striking red markings – the black widow brown recluse is remarkably easy to miss.

The pale brown spiders, about a quarter in size, spend much of their lives hidden in cracks, cardboard boxes and other dark, undisturbed corners of the house.

So what should you do if you see one?

Rick Vetter, one of the world’s leading authorities on brown recluse spiders, who has studied them for more than thirty years, has a simple answer: “Knock it down.”

And there may soon be more reasons for Americans to heed that advice.

The actual number of attacks is unknown, but reports from US poison control centers indicate that hundreds of Americans are bitten or suspected of being bitten each year. In 2024, 827 cases were recorded, including 29 that resulted in major medical complications.

Brown recluses have traditionally been concentrated in the warmer South and Midwest, but there are signs they are gaining a foothold further north.

They have been sighted in at least 10 Michigan counties, well beyond what experts traditionally consider the spider’s native range.

And scientists warn that rising temperatures could accelerate the northward creep.

A major study that mapped how the spider’s habitat could change as temperatures rise predicted that suitable territory would shift north, potentially causing brown recluses to invade parts of Nebraska, Minnesota, Wisconsin, Michigan, South Dakota, Ohio and Pennsylvania, where they have traditionally been rare or absent.

And climate may not be the only way they move.

Brown recluses have a particular preference for tight, undisturbed spaces – including the folded flaps of cardboard boxes – and can survive long periods without food.

This means they can be inadvertently transported hundreds of miles in shipments and household belongings, sometimes turning up far beyond their natural range.

And when encounters do occur, the consequences can be terrifying.

Britagne Miller, mother of four, was Kansas continued to fight for her life earlier this summer after being swarmed by about 15 spiders during a family camping trip.

“It felt like 15 spiders were climbing up my legs and up my shirt, and I’m terrified of spiders,” she said.

At first things seemed to be going well for Miller. But four days later, a bruise from one of the bites on her calf began to swell rapidly and became painfully painful.

“It was like my leg shot me in the foot, and I felt like I was being stabbed,” she said.

Doctors discovered a huge blood-filled swelling in her calf and operated to remove almost 300 ml of blood clots. But Miller already suffered from two rare blood clotting disorders and a damaged liver, making surgery exceptionally dangerous.

“I’m terrified of having surgery, that I’m going to sleep and not wake up, or that I’m going to bleed,” she said.

Her condition continued to deteriorate. She developed severe blood and staph infections and doctors believed she had entered the end stages of liver failure.

“They gave me three days to a month to live,” Miller said. “So that was scary.”

Miller survived and was eventually released from the hospital, although she now requires a liver transplant.

Experts said the location and nature of her injuries led them to believe she had been bitten by brown recluse spiders, which are common in Kansas, although the species has never been definitively identified.

Other victims were not so lucky.

In one published case, a healthy 19-year-old man developed worsening pain, fever, chills, nausea, and vomiting after a suspected brown recluse bite. He suffered kidney damage, was hospitalized, appeared to improve and was discharged – but deteriorated again several days later when the poison began to destroy his red blood cells.

Ultimately, he required three emergency room visits and two hospitalizations.

And in exceptionally rare cases, victims have died.

A healthy three-year-old girl in Tennessee developed dark urine after a suspected brown recluse bite and was rushed to the hospital, where she went into cardiac arrest and died during a blood transfusion.

Another published report documented the death of an adult from severe red blood cell destruction following brown recluse poisoning.

Despite their fearsome reputation, brown recluses are not aggressive and will generally flee rather than attack a human.

But they thrive in homes, where they wedge themselves into dark, cramped, and rarely disturbed spaces—behind picture frames, under windowsills and furniture, and in closets, attics, basements, and cardboard boxes.

And where there is one, there may be many.

In one exceptional case, researchers collected 2,055 brown recluse spiders from a single-family home in Kansas in just six months. They were found in every room, including bedrooms, bathrooms and the kitchen.

Yet the family of four had lived there for six years without suffering a single known bite.

That’s because most bites only occur when the spider suddenly gets stuck against human skin.

“Bites happen a lot in bed,” says Vetter. “A person can roll over on a spider, and the spider responds in a last-ditch manner.”

Others happen while getting dressed.

“Many women also get bitten when they put on skinny jeans,” he said. ‘It may be that the spiders crawl into the jeans at night and when someone puts them on, the spider is pushed against the skin, causing it to bite.’

Laura Rosenwald, an entomologist specializing in spiders with the National Pest Management Association, said another danger is reaching properties that have been left untouched for months.

“Brown recluses like undisturbed areas, where they cling to flat, tight spaces, such as in a cardboard box, where you can’t see them,” she said.

“And then bites happen when people put their hands in boxes they haven’t looked in for a while and accidentally catch a spider.”

The good news is that the vast majority of brown recluse bites do not lead to serious illness. Estimates suggest that about 90 percent recover without major complications.

But there is no antivenom for brown recluse bites in the U.S., meaning doctors largely have to treat the symptoms while the body deals with the venom.

Immediately after a suspected bite, experts recommend washing the area thoroughly with soap and water, applying an ice pack and, if possible, elevating the affected limb to reduce swelling.

Patients should then seek medical advice, especially as the bite may initially appear relatively harmless but become more serious over the following hours or days.

The main warning sign is dark urine.

This may indicate that the venom is destroying red blood cells throughout the body, a potentially life-threatening complication known as systemic loxoscelism. Fever, chills, vomiting, dizziness, and widespread rash may also indicate a serious reaction.

“It’s a particular risk in children,” Vetter said. ‘The most critical symptom is having dark urine, usually Coca-Cola colored. Then immediate treatment is needed.’

And if possible, experts recommend taking a photo of the spider — or safely taking the dead spider with you — so it can be properly identified.

This is important because there is no test that can prove that someone has been bitten by a brown recluse, and wounds attributed to the spider often turn out to have other causes.

There are also steps people can take to reduce the chance of ever being bitten.

Experts recommend regularly vacuuming and clearing clutter of attics, basements, closets and other areas that are rarely disturbed, making them less attractive hiding places.

Cardboard boxes can be replaced with sealed plastic storage containers, while clothes, shoes and bedding should be kept off the floor and shaken out before use, especially if they have been untouched for some time.

Sticky traps placed along walls can also help reveal if brown recluses are living in a home, while gloves should be worn when handling old boxes or other stored belongings.

But despite the horrific injuries they can cause, Rosenwald emphasizes that the spiders do not actively hunt humans.

“I always tell people these spiders aren’t heat-seeking missiles, they’re not out to bite you,” she said.

‘If they bite, it is usually only because the spider is stuck or pressed against something.

‘Taking steps to minimize the places the spider can live in your home, installing sticky traps and calling pest controllers if you see them can all reduce the risk.’