The alley-parked car is where a yard rat becomes an expensive rat.

A parked car’s engine bay is warm, dry, dark, and close to the ground. To a rat living under a shed or in an alley it is a den. Rats build nests on top of the engine from leaves, insulation, and shredded paper, and they gnaw. Wiring insulation is one of the things they gnaw, and a chewed harness can disable a car or start a fire.

In the complaints the pattern is specific. Alleys and driveways, not the street. A car that sits for days, not one driven daily. Summer, when rat complaints peak. And a yard or alley with an existing rat problem: the car is not the cause, it is the last stop.

The car complaints sit in the same places as the rat complaints: the prewar neighborhoods with alleys and detached garages, above all South Hilltop, the Near East Side, Milo-Grogan, Linden, and the South Side. They say "rat", almost never "mice". They arrive in summer. And they are usually filed as a complaint about the neighbor’s trash or yard, with the car as the damage.

A sample, trimmed and with nothing that identifies a person or a property: "Rats throughout the alley behind the house and they are chewing through the wires of the residents’ cars." "We have seen rats in our cars and they have chewed through wires. We had to pay over two thousand dollars to get it fixed."

More on where and when rats are reported: the live rats and mice page.

• Move the car or drive it. A car that moves every day is a poor den. A car that sits for a week in an alley is a good one.
• Look under the hood after a few days parked, in summer above all. Nest material on the engine, droppings, chewed insulation. Catching it early is the difference between a cleanup and a repair.
• Remove what feeds them. The car is the last stop. The pile, the open trash, the bird seed, and the tall grass are the first. That part is the city’s business if it is on someone else’s lot.
• Keep the hood area clear of leaves and debris, and the ground under the car clear too. Rats like cover on the approach.
• Check your insurance. Rodent damage to wiring is covered under some comprehensive policies and not others. Ask before you need it.

The city cannot do anything about a rat in your car. It can do something about the conditions on a lot that harbor and feed the rats: tall grass, junk, open trash, animal feed, dog waste. If the rats in your car come from a neighbor’s yard or a shared alley, that is the complaint to file. Say where the rats are coming from, what feeds them, and that they are damaging cars in the alley. How to word it.

Trash not taken to the alley collection point is a common thread in these complaints, and it is enforceable.