124 Order RODENTIA 



millions more. Its small cousin, the house mouse, is less de- 

 structive individually, but because of its greater abundance 

 causes almost as much total damage. Both the Norway rat and 

 the house mouse were introduced from Europe. 



Some of the native rodents of Illinois are responsible for con- 

 siderable economic loss. Some have direct or indirect economic 

 value. Woodchucks, pocket gophers, ground squirrels, native 

 mice, muskrats, beavers, and chipmunks do varying amounts of 

 damage to gardens, cereal grains, and silage crops. Field mice 

 and voles cause considerable loss in orchards as a result of their 

 girdling of trees, fig. 37. By their burrowing, such animals as 

 muskrats and woodchucks weaken dams and embankments. 

 Pocket gophers and woodchucks make mounds of earth that in- 

 terfere with mowing operations. Beavers construct dams that 

 sometimes cause flooding of farmland. Some kinds of squirrels 

 occasionally eat young birds and bird eggs; some may be nui- 

 sances in human habitations when they store food or make their 

 homes in attics or walls. A few native mice feed on clover and 

 grasses and they may also deface lawns with their runways. 



Among the native rodents of direct or indirect value are the 

 ground-inhabiting squirrels and mice, which play a role in soil 

 improvement by bringing subsoil to the surface and depositing 

 humus-forming material below the surface of the ground. Their 

 burrows hold excess water during wet periods and thus serve 

 as underground reservoirs during dry periods. These burrows 

 are frequently used as nests by bumblebees, which help pollinate 

 the blossoms of some crop plants. Tree squirrels and chipmunks 

 contribute to forest production by burying tree seeds in the 

 ground and failing to return for them; some of these buried 

 seeds sprout and grow. Fox squirrels and gray squirrels provide 

 food and sport for countless hunters and furnish aesthetic enjoy- 

 ment for nearly everyone. Some mice feed on insects and may 

 aid in the control of insect pests more than is realized. Most 

 species of rodents serve as food for valuable fur-bearing mam- 

 mals. Woodchucks make and desert numerous burrows that are 

 used by furbearers as dens for rearing their young and by cotton- 

 tails as shelter from harsh weather. 



The muskrat is the most important fur resource of Illinois. 

 Each year an estimated 20,000 people in Illinois harvest musk- 

 rats; the annual value of the furs they take is somewhat under 

 a million dollars. 



