NEW ENGLAND FARMER. 



155 



For the New England Farmer. 

 CANKER WORMS. 



BY T. W. HARRIS. 



Canker-worm moths have already made their 

 appearance. My trees were tarred on the 10th of 

 March, and many of the moths came out of the ; 

 ground and were caught in the tar during the night 

 of the 13th instant. Others may be expected to 

 appear till the end of the month, and will endeavor 

 to ascend the trees in order to deposit their eggs. 

 A few of the parent insects may lay their eggs on 

 the trunks of the trees; but the greater number 

 proceed to the extremity of the branches, and de- 

 posit them in small clusters, upon the twigs and 

 buds. The trees most subject to the attacks of 

 canker-worms are the apple, cherry, plum, moun- 

 tain-ash, linden, and elm. When trees have been 

 exposed to the unchecked depredations of these 

 insects during several successive years, they be- 

 come impaired in vigor, and decay prematurely. 

 In order to protect them, they should be tarred 

 seasonably and repeatedly in October and Novem- 

 ber, and again in March ; or some other approved 

 and effectual remedy should be employed, to pre- 

 vent the parent insects from ascending the trunks 

 and laying their eggs. A large proportion of the 

 insects that rise in the autumn are wingless fe- 

 males ; and, on the contrary, more males than fe- 

 males ascend in March. It seems difficult to ac- 

 count for this disparity of the sexes at these two 

 seasons, unless some of the females survive the 

 winter upon the trees, to pair with the males in 

 the spring. I am not aware, however, that any 

 observations have been made confirming this sug- 

 gestion. The eggs are hatched about the first of 

 May. The young canker-worms, then less than a 

 twentieth of an inch in length, immediately conceal 

 themselves in the opening buds, and begin to eat 

 the leaves before fairly expanded. They are very 

 injurious to grafts, and sometimes entirely destroy 

 the buds before their presence is discovered or 

 suspected. A thorough syringing of these, and ofi 

 small trees and shrubs, with a solution of whale- 

 oil soap, has appeared to be a good remedy. This 

 application may be made in May and early 'in June, j 

 When trees, infested with canker-worms, are sud- 

 denly jarred or shaken, the worms drop off, and 

 hang suspended by threads, but soon climb up; 

 again by means of these threads. If, however, I 

 the connection of the dangling worms with the 

 trees be broken off by striking the threads with a 

 pole, the insects will have no means of mounting 

 the trees again but by creeping up the trunks, and 

 this they may be prevented from doing by a belt 

 of tar about the trees, or by leaden troughs filled 

 with oil. 



Many kinds of destructive insects are found to 

 prevail^ and to disappear at irregular intervals. 

 Beginning with a few, they continue to increase in 

 numbers during several successive summers, till at 

 length, after a season marked by an extraordinary 

 abundance of them, they retire from the scene of 

 their depredations, not to return in the same force, 

 for several years. During such intervals, when 

 none or few are seen, vegetation, if not too much 

 exhausted, has time to recover before the reap- 

 pearance of new and successively increasing 

 swarms of the spoilers. Among the insects, whose 

 irregular visitations and disappearance have been 

 observed, are rose-bugs, cherry-slugs, grasshop- 

 pers, apple tree caterpillars, salt-marsh caterpil- 



lars, and canker-worms. The cause of the disap- 

 pearance of these insects seems not to be well un- 

 derstood. Various reasons have been assigned 

 therefor, such as wet weather, cold winters, pes- 

 tilence, and the diminution of their accustomed 

 food. The true cause seems to have been over- 

 looked, namely, the rapid increase of the natural 

 enemies of these insects, which, in the course of a 

 few years, become so numerous as to overpower 

 them completely, and put a sudden stop to their 

 depredations. 



Canker-worms bave many enemies. They are 

 devoured by moles, and by various kinds of birds, 

 such as the king-bird, oriole, black-poll warbler, 

 black-throated bunting, chickadee, and especially 

 the cherry-bird, which lives almost entirely upon 

 them till cherries begin to be ripe. They are eat- 

 en by a very large and splendid green beetle ( Ca- 

 losoma scrutator,) that appears about the time when 

 these insects begin to leave the trees. These beetles 

 do not fly, but they run about in the grass after 

 the canker-worms, and even crawl up the trunks 

 of the trees to catch them as they come down. 

 During the prevalence of canker-worms, in the 

 years 1839, 1840, and 1841, great numbers of 

 these beetles were observed in Cambridge, where 

 they have been seldom seen at other times, and 

 many were thoughtlessly crushed under foot in 

 paths and the highways. The potter-wasp (Eu- 

 menes fratcrna,) an insect rather smaller than the 

 common brown wasp, fills her clay cells with full- 

 grown canker-worms, often gathering eighteen or 

 twenty of them to supply her future brood with 

 food. A i'our-winged ichneumon-fly, also stings 

 them, and lays in each one a single egg, from 

 which is hatched a little maggot that consumes 

 the fat of the canker-worm, and causes it to mis- 

 erably perish. I have seen one of these ichneu- 

 mons sting several canker-worms, in succession, 

 and swarms of them may be observed around the 

 trees as long as the canker-worms remain. Among 

 a large number of canker-worms, taken promis- 

 cuously from various trees, nearly one-third were 

 unable to finish their transformations, in conse- 

 quence of being preyed upon by the maggots of a 

 two-winged fly, or Tachina. Even the eggs of the 

 canker-worm moth have their parasites, which de- 

 stroy great numbers or prevent their hatching. 

 This kind of parasite is a tiny four-winged fly, a 

 species of Plalygaster, which goes from egg to 

 egg, and puncturing them, drops one of her own 

 still smaller eggs in each. Sometimes every egg- 

 in a cluster will be found to have been thus punc- 

 tured and seeded for a future harvest of the Platy- 

 gaster. The young parasite, batched within t) o 

 canker-worm egg, the shell of which, though only 

 one-thirtieth of an inch long, serves for its habita- 

 tion, and the contents for its food, is an exceeding- 

 ly minute maggot, which becomes a chrysalis -with- 

 in the same shell, and finally is transformed to a 

 Platy garter fly like its parent. All these eneioie? 

 will be found to abound when canker-worms ha\ 

 prevailed during several years ; and to them el iefl\ , 

 if not alone, I cannot but attribute the suddu, 

 check that was given to the further increase i i 

 these destructive insects in the summer of 1841, 

 when their ravages seemed to have reached their 

 height in this vicinity. From that time till the 

 year 1847, scarcely a canker-worm was to be seen 

 here. But the race was not extinct ; and enough 

 continued and multiplied, year after year, to seed 



