At first, Jamie Engelmann didn't make much of a red bump in her daughter's groin. Earlier that day, Thea Skladanoski, 2, had been playing in the grass of her grandfather's yard in Holmesburg. "It just looked like a diaper rash or a hive the size of a pimple," Engelmann said. Thea pouted and scratched herself. But two days later, when the bumps spread up Thea's arms, Engelmann rushed her to the hospital.
Nearby, something similar was happening to George Kirk, 7, in Mayfair. He also had been playing on the grass, while his mother, Pamela Leisey, looked on from the patio. She had seen red ants marching across the area before but never considered them dangerous.
"Then, George had these huge, dark red bumps that looked like the chicken pox all over his face, neck, underwear lines, and legs," Leisey said. "And George would say, 'Mom, you got to stop this itching!' " So she sought medical attention.
Barbara Gold, a pediatrician at St. Christopher's Hospital for Children, immediately diagnosed both children with fire ant stings. The doctor herself was stung twice in the last two months at a community garden in Spring Garden.
"The telltale sign of a fire ant sting is the tiny white pustules that form on top of clustered red bumps," Gold said. Over the Memorial Day weekend, Gold was clued in to the symptoms when she witnessed her 10-year-old grandson get stung in Texas.
The heat of Southern states is perfect for the most aggressive species: the red imported fire ant, Solenopsis invicta. A cargo ship that docked in Mobile, Ala., likely introduced the species from South America in the 1930s, according to genetic analyses.
But the concentration of red imported fire ants is five to 10 times greater when found in the United States than in South America, said Sanford Porter, an entomologist at the U.S. Department of Agriculture in Gainesville, Fla. About half the population of urban areas in the South is stung every year, studies have shown.
"When the imported fire ant arrived in the U.S., it didn't have to pay any of the taxes," Porter said. "That is to say, it doesn't have any of its natural enemies here."
Porter grows one such enemy, the phorid fly, in his lab for dispersion across Southern states. The fly hovers a few millimeters above the ants before it deposits an egg between their legs, producing a maggot that grows inside the ant's body and decapitates it within two weeks.
Fire ants cost the U.S. an annual $6 billion in pest control, crop damage, and equipment repair, according to the U.S. Department of Agriculture. Pesticides can help.
But fire ants may not be entirely bad. Researchers at the Georgia Institute of Technology study the ants' movement in tunnels with the hope of using that information to design underground robots for search-and-rescue missions.
Michael Goodisman, a biologist on the team, doubts ants will become a local problem. "It's totally weird to hear that you have fire ants in Philly," he said. "I'm stunned, but the fire ants are not tolerant enough for the cold winters there."
The ants' attack mechanism is worthy of a horror movie. Their sawlike teeth first dig into human skin. Their bulky abdomens then reel inward and repeatedly sting, injecting venom, often in a circular pattern.
Less than 1 percent of stings cause an allergic reaction to the venom. Most resolve within two weeks with antihistamines and over-the-counter corticosteroid creams. If symptoms worsen, see a doctor. A prescription for antibiotics may be needed if infections develop.
To avoid getting stung by fire ants, stay away from large dirt mounds, where several hundred thousand ants may be living just underneath. Fire ants are the same size as common garden ants but more reddish in color.
Even if the ants are here to stay, Goodisman suggests there's no need to worry. Over the course of his career, he has been stung countless times. "I'm sure you'll also get used to them," he said.
Contact Leila Haghighat at 215-854-4869 or email@example.com.