Raymond Grenier, age 12, of West Warwick, Rhode Island, for his question:
How closely are rats and mice related?
A frisky little house mouse looks for all the world like a miniature copy of the ordinary house rat. Further investigation reveals that their teeth and other internal features are alike except in size. They also feed on similar foods and live similar lives.
The only differences between the ordinary rats and mice are size and weight. The everyday house rat measures about 16 inches from his nose to the tip of his tail and he may tip the scales at 14 ounces. The bitsy house mouse has a total length of about 3 1/2 inches and when well fed, he may weigh one ounce. Both animals have long pointed snouts with whiskery moustaches, bright beady eyes and round leafy ears. Both scuttle around on soft bare feet and both have bare, rather scaly tails as long as their bodies. Both have four front incisor teeth and 12 molars. Neither mice nor rats have any canine or premolar teeth.
The most remarkable feature of these animals is their front incisors. These are special gnawing teeth that continue to grow throughout life. Teeth of this sort dic¬tate the sort of life an animal must live. Their tops are filed down by gnawing, and if not kept in check, they grow right through the jaws and lock the mouth shut. They compel the animal to gnaw on hard substances every day. All animals having such teeth are classified as rodents. Rats and mice are rodents of the huge animal order Rodentia. Their kinfolk include. the beavers and the guinea pigs, the squirrels and the porcupines.
The Order Rodentia is subdivided into a number of smaller families and the rats and mice have the Family Muridae all to themselves. Their family membership outnumbers all the others and the teeming swarms of rats and mice in our land are estimated to outnumber all our other four footed animals. Among both rats and mice there are variations in size, color and habitat. The musk rat loves the water, the white footed mouse prefers life in the woods. Based on these variations, zoologists classify the Muridae Family into a large number of genera. And, of course, each identical rat or mouse has his very own species classification.
Both rats and mice tend to be night prowlers. They are burrowing animals who pre¬fer to keep out of sight. They are also very hungry animals and always eager to devour almost any kind of food, meat or vegetable, soft or tough. Rats, as a rule, prefer to eat meat and often prey on their small, mousey brethren. The hungry little mice eat meat as well as any other available food. But when well fed and given a choice, they prefer to dine mostly on grains and vegetable foods.
The ordinary house rats and house mice have always lived very close to human habitations, always trying to pretend that they are not there. This is because they depend upon our food stores. Since time began they have secretly raided our pantries and granaries. Every year the damage they do by devouring and destroying our food is immense. They also carry diseases. For these reasons the little wretches are rated as pests and it is everyone's duty to help to exterminate them.