Wendy Berry and her rat-hunting dogs are coming back to Maine to help homesteaders place a special rat fertility control formula on their property. Credit: Julia Bayly / BDN

Over the years people have tried a lot of ways to control rat populations on farms using traps, poisons and even hunting them with cats or dogs. Now there’s a new option: promoting rodent safe sex.

Given that one female rat is capable of producing 1,500 offspring in a single year, birth control would seem like a no-brainer. That is why rat-hunting expert Wendy Berry is returning to Maine this spring with her trained dogs and bait that contains rat birth control chemicals.

“As we all know, the rat population explosions can happen overnight,” Berry said. “People who notice a huge increase in rats say they can’t catch them fast enough — this rat birth control gives humans an advantage.”

Berry was in Maine last fall with three of her rat-hunting terriers. She and the dogs visited several homesteads where they located and killed dozens of rodents. This time, Berry said her dogs will use their skills to help property owners locate areas of rat congregation where the birth control bait can be placed to have the best chance of working.

The bait was developed by researchers at the University of Arizona. It has only recently come on the market under the trade name ContraPest.

According to Berry, one of the big advantages to ContraPest is that it works on both male and female rats.

Female rats — like all female mammals — are born with all the eggs they will ever produce. ContraPest destroys the rodents’ ovarian follicles that contain those eggs. It basically forces the female rat into early menopause, something that would happen naturally over a longer period of time.

In male rats, the chemical formula halts sperm production.

“The dosage used for rats is so mild and so low, it presents no harm to any other animals,” Berry said. “It does not bioaccumulate, so there is no danger to any pets or wildlife that might eat a rat that has consumed the birth control.”

Birth control could be a good outside-the-box strategy, according to Griffin Dill, integrated pest management professional at University of Maine Cooperative Extension, who has worked in pest management for years.

“Stopping the reproductive success as a control method is an interesting avenue that has potential,” Dill said. “Any research in that direction to steer us away from the lethal options that have downstream effects on wildlife and pets is good.”

At the same time, Dill reminds property owners that the tried and true methods of rat control, such as trapping and dogs, should not be abandoned, especially now that rats are entering a peak breeding season with the longer days and warmer temperatures.

“The most important things in controlling rats are sanitation and exclusion,” Dill said. “Whether it’s a home, farm or even an office building, look around and find what rats are feeding on or could be feeding on.”

Fruit and vegetables left on the ground from last season’s gardens are prime rat feeding areas, according to Dill. He recommends cleaning out those areas as the snow melts.

“Removing the food sources is one of the biggest ways to prevent or resolve a rat infestation,” Dill said. “If there is no reason for the rats to stick around — and that reason is generally food — they are not going to stick around.”

Now is also the time to look for any holes where rats can enter buildings and seal them up.

“That can be a challenge,” Dill said. “Those sources of entry can be pretty small.”

Berry said using fertility control bait could be a great addition to those measures.

“This would be a really good key for an attack on multiple ends,” Berry said. “It will give someone a chance to trap rats without having to worry about an explosion in the population.”

Berry plans to work directly with farmers or homesteaders using her dogs to identify the areas best suited for the bait traps.

“We want to hit the rat community areas where they have their lounging and sleeping areas,” she said. “The dogs will locate where those are.”

As a bonus, if her dogs can successfully hunt and kill any rats, they will be free to do so.

“The dogs will go immediately where there is a lot of rat activity,” Berry said. “I can tell by their reactions how many rats there are in that spot.”

The bait is loaded with things that taste good to rats, so when one discovers the treat, it goes back and lets others in the colony know so they, too, will go feed on it. Once consumed, the fertility controlling formula starts to work within a matter of days.

ContraPest bait stations include a two-month supply of the rat birth control formula and cost $69. The stations, also available directly from ContraPest, are hinged plastic boxes that, once baited, are placed near areas of known rat activity.

As the rat breeding season ramps up over the coming weeks, Dill said the combination of the new formula and what’s worked in the past is one to watch.

“Combining laboratory and scientific methods with more folksy methods like using dogs that have been used for centuries is an interesting dual use of new and old,” Dill said.

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Julia Bayly

Julia Bayly is a reporter at the Bangor Daily News with a regular bi-weekly column. Julia has been a freelance travel writer/photographer since 2000.