CHICAGO (CBS) — An invasion in Lincoln Square is making local residents’ skin crawl. Rats – some say up to 20 at a time – have been scampering through people’s yards.

As CBS 2’s Mike Parker reports, city officials said it’s been baiting alleys because they’ve received so many complaints.

Lincoln Square residents said that, all summer long, an upscale 4800 block of North Seeley Avenue has been overrun with rats.

Sara England said she counted 15 to 20 rats in her yard one night last week.

“And they were the big ones,” she said, placing her hands more than a foot apart.

She said she and her dinner guests were stunned.

“So we brought out some flashlights and looked at all the rats underneath us and it was like an urban safari,” England said.

In Becky Gillespie’s back yard, two rats have been snapped up in traps since Tuesday night.

“So now I can’t let my kids play out here at night,” she said.

She said she was worried about possible diseases the rats might be carrying, as well as the chance the rats might bite her children.

“I mean, you never know,” Gillespie said. “About two weeks ago in a 15 minute period, I counted 20 running through my back yard.”

In the alley, there are warning notices that the city baited the area on Tuesday.

“I just want to see what happens with it. I’m a little concerned about … my children and my pets,” England said.

The move to bait the alley came after residents like Gillespie complained to the local alderman and his staff.

“They were all sort of horrified at what we are telling them,” Gillespie said.

The city has issued a cleanup order to the owner of a garbage-filled garage in the neighborhood. The suspicion is it’s a haven for rats.

The complaints come nearly six months after the city began cutting back rodent control efforts. In March, the Streets and Sanitation Department moved rodent control and the forestry bureau to garbage control.

But the city does offer some advice for keeping rats away.

As the city points out on its official Web site, rats have an average lifespan of 6 to 12 months. Females can produce four to seven litters per year, and came become pregnant again within 48 hours of giving birth.

While rats prefer fresh food, they will eat pet food, dog feces, garbage and plants too, the city pointed out.

The rats in Chicago are Norway rats, which prefer to live in burrows in the ground, and can climb and swim easily. They can also chew through wood and plaster, crawl through holes the size of a quarter, tread water for three days, and land safely after a five-story fall.

But the most worrisome aspect of wild rats in Chicago is the risk of disease. They carry a variety of infected fleas and ticks that can be passed on to people, and if cornered, they can bite, the city points out.

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