Starting this spring, the Chicago Transit Authority is making birth control free and conveniently located—for rats. It’s using the contraceptive ContraPest to curtail the rodent population in what Orkin has crowned America’s most rat-infested city. (We’re No. 1 for bedbugs, too. Getting itchy yet?) Chicago is particularly rat friendly because of its age and extensive underground infrastructure, according to Ron Harrison, Orkin’s director of technical services: “It just provides a wonderful haven for them.”

The CTA doesn’t know exactly how many whiskered vermin it’s fighting—rat studies are notoriously inaccurate. Complaints to the city last year were actually down 3.6 percent from 2013, according to the Department of Streets and Sanitation. But the CTA considers its family planning a preventive measure. How effective is ContraPest? Its manufacturer, SenesTech, estimates that the number of rats in New York subway stations declined 43 percent after its use there last year.

What ContraPest Is

Described as a “milky egg cream” consisting mostly of fat and water, the contraceptive includes a chemical called 4-vinylcyclohexene diepoxide, or VCD. According to SenesTech, rats’ discerning palates prefer the sweet-­smelling formula to garbage. It also hydrates rats—unlike mice, they need water every day—which brings them back for more.

Where It Will Go

Mostly where CTA riders don’t, such as bus and rail garages. Many of these century-old structures have nooks and crannies that make prime rat burrows. The contraceptive sits in liquid or solid form in a black plastic box with openings small enough to prevent children and pets from accidentally eating it. The CTA will replace it every 15 to 20 days.

How It Works

VCD speeds up egg loss in female rats, and a plant-based ingredient halts sperm production in males. (Attention, PETA: SenesTech is careful to point out that ContraPest has few, if any, side effects.) The more of it rats eat, the more effective it is. Most rats are rendered permanently sterile within 8 to 12 weeks, though some superrodents live long enough to regain fertility.


Rat Math

Left unchecked, a rat population can get out of control quickly. (Use our model to see just how quickly.)

Average lifespan of 8 to 12 months
Fertile at 2 months
4 to 7 litters a year
9 to 12 pups a litter
Up to 15,000 descendants a year from one rat



Rattiest Cities in America


1 Chicago

2 Los Angeles

3 Washington, D.C.

4 New York

5 San Francisco

NOTE: Based on Orkin rodent treatments in metro areas in 2013

Four Reasons Rats Are Grosser Than You Think

gallon icon

1. They pee a gallon of urine a year.


2. They poop 40 to 50 pellets a day.


3. They carry E. coli and salmonella, “dribbling everywhere,” Orkin’s Ron Harrison says.

Naked rat

4. They shed all their hair twice annually—and your HVAC system blows it around the house.