Contraceptives Help Keep Finland’s Rats Under Control

Rats aren’t much of a problem in clean, cold Finland, and Kalle Heiskanen hopes to keep it that way. So he feeds them contraceptives.

He said he has come to like the rats and doesn’t want them wiped out, just kept to manageable numbers.

Have people laughed at Heiskanen?

“Sure. I was labeled Rat Professor, Hormone Heiskanen . . . the village clown.”

But, he added, “playing the flute would only mean taking the problem elsewhere”--a sly reference to a legendary piper who solved a rat problem in Hamelin, Germany, in the 13th Century.

People also have taken him seriously.

“It seems we could apply this kind of experiment on a larger scale,” said Matti Valtonen of the Agriculture Ministry. “We have no clear proof that it works . . . but if it does, we are onto a winner.

“What Heiskanen is doing seems to be simple, cheap and, above all, safe. He is cutting out the necessity of using poisons, and that we must welcome.”

Heiskanen, 42, has worked as a sailor, bartender and construction worker. While convalescing from a construction accident that broke both his legs, he learned from a television program that rats were a major spreader of disease.

“I just thought that, in this modern age, with electronic equipment and advanced weapons systems, it’s strange that we cannot control an age-old pest like rats,” he said.

Poison is the usual method, but Heiskanen did not like that.

“Any animal or bird of prey feeding on or attacking a poisoned rat is done for,” he said. “I’ve seen lots of cats and dogs suffer because of it.”

What better way to reduce the rat population than by keeping more from being born, Heiskanen thought. That took him to the University of Joensuu, near this town of 3,000 people in eastern Finland, to ask about contraceptives.

Scientists at the university suggested progesterone, a hormone that resembles substances used in contraceptive pills. University pharmacists provided Heiskanen with a mixture of progesterone and cooking oil, and advice on how to feed and observe rats.

The Kesalahti Council gave him a $500 grant and he went to the garbage dump on the edge of Kesalahti, 10 miles from the Soviet border.

He lived there in a trailer for two months, feeding 600 to 700 rats every night with bread soaked in the progesterone mixture. He continued his nighttime patrols afterward, and said the rat population had shrunk by about 15% in four months.

“I can well believe it,” said Heikki Hyvarinen, biology professor at the university. “There is no reason why feeding contraceptives to rats should not work. After the two-month period, when we studied a dozen or so female rats, we found every one of them infertile.”

A female rat can give birth when it is 35 days old, has six to 14 offspring and ovulates again in four days. Its average life span is three years.

Risto Asikainen, a Kesalahti county official, said poisoning rats “is expensive, it pollutes the environment and seldom are the strict safety measures adhered to.”

The law stipulates that carcasses of rats killed by poison be burned, but dying rats often evade detection by digging themselves deeply into holes and crevices.

Hyvarinen said the university plans a more detailed and scientific study of the rats at the garbage dump this spring.

“Heiskanen’s results are promising,” he said. “It is a clean and cheap method and could possibly be the best way of dealing with the rat problem, particularly in Third World countries.”