Soon, though, the mark started to grow and turned black.
Donovan took her daughter to the hospital, where infectious disease specialists told them that it was from a black widow spider bite, CBS News reports.
"I didn't know what to say," the girl's father, Josh Donovan, said to local news station WCVB.
"It's not something you would expect." A 5-year-old Mendon girl who was bitten by a black widow spider is recovering.
While a black widow bite won't put a person's life in danger, according to Nat Geo, it can be painful and cause some "internal problems." Symptoms of a black widow bite can include anxiety, difficulty breathing, painful muscle cramps, headache, high blood pressure, increased saliva, increased sweating, sensitivity to light, muscle weakness, nausea and vomiting, numbness, and restlessness.