Illinois Natural History Survey - University of Illinois

The Naturalist's Apprentice: Shrew Mathematics

Objective: to understand that shrews are important members of the food web in any yard, field, or woods in Illinois, and to understand what it means when it is said shrews have a high metabolism.

Materials: Multiple copies of "Shrew Mathematics," calendars, calculators.

Comments: Adult short-tailed shrews range in weight from 11 grams to 27 grams. Males tend to be slightly larger than the females. Shrews have been shown to be important in controlling outbreaks of insects. When calculating how many quarter-pound hamburgers a person would have to eat, include only the weight of the burger, not the bun or other ingredients.

Procedure: Read the questions on the following page and calculate the answers. You will need to know the number of days in each month, and each student should know his or her own weight.

 

Answers 

1. A shrew weighing 19 grams would need to eat 28.5 grams of insects. It would take 9 1/2 grasshoppers each weighing 3 grams to weigh 28.5 grams. Since a shrew cannot kill half a grasshopper, it will kill and eat 10 grasshoppers a day.

2. If 10 grasshoppers are eaten in a day, 70 can be eaten in a week.

3. There are 122 days in a growing season. One shrew can eat 10 grasshoppers a day, so it can eat 1,222 grasshoppers in a growing season. Three shrews can eat 3,666 grasshoppers.

4. For each pound of body weight, you would need to eat 6 hamburgers. For each 10 pounds of body weight, you would eat 60 burgers. For each 50 pounds you would need to eat 300 burgers. A 100-pound person would need to eat 600 quarter-pound hamburgers a day. Just think how much ice cream you could eat!

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Shrew Mathematics Excercise

 

The short-tailed shrew is a ravenous predator that is found throughout Illinois. Although it is seldom seen, it is common. There can be as many as 50 shrews living on one acre of land. In woodlands in Illinois, there are commonly 10 to 20 shrews per acre. They are less common in grassy areas. Few animals are as hungry as a shrew. It must eat 1 1/2 times its own body weight in insects and other small animals in a single day. Solve the following problems so you can picture how much a shrew really eats.

1. The short-tailed shrew must eat 1 1/2 times its own body weight in insects each day. If a shrew weighs 19 grams and a grasshopper weighs 3 grams, how many grasshoppers must a shrew kill and eat in one day? (Count each grasshopper killed in a day. If only part of a grasshopper needs to be eaten, count the whole grasshopper. For instance, 2 1/2 grasshoppers needed in a day would be three grasshoppers killed and eaten).

2. How many grasshoppers must it eat in one week?

3. If three shrews live in your garden, how many grasshoppers can they eat in one growing season? (Consider June, July, August, and September as the growing season).

4. If you had to eat as much as a shrew (1 1/2 times your body weight), how many quarter pound hamburgers would you have to eat in one day?

Carolyn Nixon, Center for Economic Entomology



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