June 06, 2020

Biologist gives tips on rat extermination

MACHIAS — Some people may recognize late winter and early spring as the dirtiest and ugliest time of year.

Roads turn to gravel, shoes track mud onto floors, and bees spring-clean by kicking out their weak and their dead. Rats, already noted for not being clean, add a dimension to the ugly side of springtime by fighting and biting until about April 15, when their numbers reach a low curve.

According to Edwin Butler, wildlife biologist for the U.S. Department of Agriculture, division of animal damage control, this is the time of year when young male rats are getting thrown out of their nests by older and tougher rodents.

Two species of rats are found almost throughout the world. The brown rat, also known as the Norway rat, house rat, gray rat, barn rat and wharf rat, is the larger of the two. It attains a length of almost 16 inches, including the tail, which is about 7 1/2 inches long. It carries fleas which transmit diseases. The black rat is the smaller of the two species.

The average rat weighs about 1 pound, Butler said, depending on the quality and amount of food available within the colony.

They are extremely prolific, breeding three to five times a year, and usually producing eight to 14 young in a litter. Springtime is prime time for breeding.

Butler said he doesn’t become regularly involved in the extermination of rats because he doesn’t want to compete with professional exterminators. He does provide technical assistance to individuals and communities that may be having problems with rats or other animals invading homes or damaging stocks of food.

Although there are as many as 100 commercial rodenticides available for purchase, the U.S. Department of Agriculture favors the use of zinc phosphide concentrate, a natural material that resembles black powder.

To be palatable to rats, it must be mixed with fresh meat, catfood or dogfood. “Rats are fussy. They prefer fresh vegetables and meats, what you would have on your table,” he said. The mix is 1 ounce of rodenticide to 4 pounds of meat.

One pound of zinc phosphide rodenticide costs about $13. Mixed with a chemical Vitamin D additive, it can be regurgitated by dogs and cats. Rats, unable to do the same, “die quickly from a one-dose feeding. It is a quick, lethal agent,” Butler said. It reacts with the rat’s intestinal juices to create phosgene gas in the stomach.

“Because rats are smart, one may taste just enough of a bait to sense that it is dangerous to him and not eat it. If that happens, he won’t be back to touch that bait for a month or two,” the biologist said.

He cautioned that all rat baits should be deposited in a ground burrow and covered with a refrigerator or other metal cover that cannot be removed by other animals. “This is a good time of year to bait rats because raccoons are still dormant,” he advised.

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