SHADE TREE INSECTS 



79 



TREE INJURY BY SQUIRRELS 



By E. M. Mills, Assistant Biologist, U. S. Biological Survey, Amherst, Mass. 



The damage to shade trees inflicted by squirrels closely resembles insect damage, 

 particularly in the case of twig injury after it has healed. A knowledge of the 

 habits of both squirrels and insects is essential for differentiating between the types 

 of shade tree injury. In a general way damage by squirrels can be distinguished 

 from insect injury by the time of year at which it occurs. Most squirrel damage 

 is done during winter and spring, while insect injury occurs during the warmer 

 months of summer. Injury to shade trees by squirrels should not be confused 

 with that caused by deer or certain birds, such as the pine grosbeak. 



Injury to Seeds, Nuts, Fruit, and Buds. The staple food of the red and gray 

 squirrels consists of seeds, buds, and nuts of many deciduous trees and seeds of 

 conifers. In fall and winter, hickory nuts, chestnuts, beechnuts, acorns, and other 

 nuts are the important items of food and are often stored for use during periods of 

 severe weather. Squirrels also consume the seeds from the cones of such trees 



as pine, spruce, fir, and hemlock. 

 These cones are often buried in the 

 ground during the fall to be recovered 

 later in the year. Squirrels will attack 

 such fleshy fruits as the berries of the 

 flowering dogwood, apples, pears, and 

 other fruits of shade and ornamental 

 trees, mainly for their seeds. In 

 spring, the buds of maple, elm, beech, 

 ironwood, birch, willow, poplar, and 

 spruce are consumed eagerly and in 

 large quantities. 



Injury to Twigs. Probably the most 

 serious type of injury to shade trees 

 by squirrels is the cutting of twigs. 

 When ground food is not available 

 because of heavy snow, the squirrels 

 resort to feeding upon twigs. In 

 coniferous plantings they cut off 

 sharply the leader or terminal shoots, 

 chiefly to feed upon the cluster of buds 

 and sometimes the ends of the top 

 branches. This causes the trees, 

 especially Scotch pine and Norway 

 spruce, to become stunted or deformed. 

 An interesting account of injury to elm twigs is given by Professor Deuber of 

 Yale University. He observed two gray squirrels making their entire diet on elm 

 seeds during the latter part of May and early in June. They cut off twigs with 

 fresh leaves in order to reach the seeds more easily, the twigs falling to the ground. 

 In one day he found 892 twigs on the ground. In another case, two pairs of 

 squirrels in a little more than one day cut 2,886 twigs with 14,430 leaves. The 

 tree had been sprayed with arsenate of lead, but the squirrels were not deterred. 



Injury to Bark. Squirrels occasionally gnaw the bark, or girdle trees, The 

 sugar maple seems to be the most attractive to them as they relish the sap. Both 

 large and small branches may be chewed. Similar injury to coniferous trees 

 has also been reported. Damage to the bark may be in scattered patches through- 



Elm Twigs, in Seed, Removed by 

 Gray Squirrels. 



Courtesy, Conn. Agr. Expt. Station. 



