When Kristine Donovan noticed a small, purplish-blue mark on the back of her 5-year-old daughter Kailyn’s right knee, she was only slightly concerned.

As a mother of a young girl, Kristine is used to seeing small bruises on her active and rambunctious daughter. However, when the ‘bruise’ started to become nastier and bigger, Kristine immediately grew concerned. And when little Kailyn came down with a fever just a few short days later – the 5-year-old was rushed to the emergency room.

Over the course of the next couple weeks, Kristine and Josh Donovan, the parents of Kailyn, waited nervously for their young daughter to heal. What they were not prepared to hear was that their daughter’s once seemingly harmless ‘bruise’ was in fact a bite from the deadly and venomous black widow.

“We never in a million years thought it would be a black widow spider,” Kristine, of Mendon, Massachusetts, told TODAY.

The entire ordeal first started when Kailyn complained that her jeans hurt while she was wearing them.

At first, Kristine thought the jeans must be too tight and were pinching around her daughter’s knees. However, that night, while Kailyn was getting in her pajamas, Kristine noticed the little ‘bruise.’

“We never thought it was a bite or anything at the beginning,” she said. “There was no bite mark.”

When the bruise turned into something more sinister, they took her to the doctor where they determined it was indeed a spider bite – they just didn’t know which kind of spider.

The doctors prescribed the young girl with antibiotics and sent her home. But the next day – Kailyn was admitted again, given intravenous antibiotics, and more medication to take home. Everything seemed to be getting better.

Soon, Kailyn’s fever was gone and it was time to graduate preschool. But Kristine noticed the area on her daughter’s leg was reddening.

“I had a feeling that the bite didn’t look right,” Kristine said. “It started to get really nasty.”

Kristine rushed Kailyn to UMass Memorial Medical Center in Worcester, Massachusetts where doctors decided to try a different type of antibiotic. Then the next day, Dr. William Durbin a pediatric infectious disease specialist, diagnosed her with the black widow spider bite.

“I didn’t think they were around here,” Kristine said. “I was pretty shocked.”

Dr. Durbin only sees about 2 or 3 cases of black widow bites a year – but unlike other bug bites, their venom causes necrosis, when the skin dies and turns black.

Kristine was shocked to hear the diagnosis, but it was spot on with her daughter’s symptoms. The ‘bruise’ had now turned black and was surrounded by red and infected skin.

“That’s a very unusual and distinct reaction,” Dr. Durbin told TODAY. “I diagnosed her with a spider bite, presumably a black widow because that’s the only spider in New England that I know of that causes this kind of reaction.”

Kailyn was given yet even more antibiotics as the course of treatment only treats the skin infection, not the bite itself.

“She was not severely ill,” Durbin said of Kailyn. “The bite looks nasty, but it wasn’t causing any serious illness in her.”

Black widow spiders aren’t uncommon in the United States, however, they are most commonly found in the West and in the South. You’ll often find the venomous spider living in barns, wood fences, and sheds.

Kristine believes that the spider must have been disturbed after her husband had been clearing the yard. The Donovan children went out to play in the clearing and that’s when Kristine believes her daughter was bitten.

Kristine wants Kailyn’s story to remind parents to trust their instincts if they feel something isn’t right.

“We just want parents to trust your instincts,” she said. “If you feel something doesn’t look right, just keep going to the doctor to find out what it is.”

As for Kailyn? She’s back to being a happy and energetic little girl who just wants to play!

Watch the full story in the video below.

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H/T: TODAY