2l8 



NA TURE 



[July 9, 1891 



make burrows, passages, and galleries in trees, mainly 

 just under the bark. Of these, the elm-tree borer, 

 Saperda tridentata, is prominent, often killing elm-trees 

 by wholesale, both in forests and in public parks. The 

 larvae bore in the inner bark, making irregular furrows 

 and tunnels upon the surface of the wood, which " is, as 

 it were, tattooed with sinuous grooves, and the tree com- 

 pletely girdled by them in some places." In the State of 

 Illinois attention was attracted to the gradual decay and 

 death of white elms {Ulmus americanus) in rows in 

 some towns. The leaves fell off in the summer, and 

 some of the branches died. Finally, the tree perished 

 altogether. On peeling off the bark, half-grown larvas 

 of Saperda tridentata appeared in considerable numbers, 

 and the manner in which the bark had been mined by 

 the Saperdas gave sufficient evidence of the cause of the 

 death of the tree. Prof. Forbes, State Entomologist of 

 Illinois, says : " From the present appearance of the 

 elms throughout the towns of Central Illinois, it seems 

 extremely likely that this pest will totally exterminate 

 this tree, unless it be promptly arrested by general 

 action." It is recommended that all affected trees 

 should be removed and destroyed in autumn and winter, 

 before the beetles have a chance to emerge from the 

 trunks. This beetle is not quite an inch long ; its larva 

 is rather more than an inch in length, having a large flat 

 head. 



Fir trees, especially the white pine {Piiius strobus), the 

 yellow pine {Pinus mitis), and Pinus rigida, are much 

 injured by the pine borer or " sawyer," Monoharnmiis 

 coiiftisor. " I have seen," writes Dr. Packard, " hundreds, 

 perhaps nearly a thousand, dead firs, whose trunks were 

 riddled with the holes of these borers." Dr. Packard 

 cites a correspondent of the North- Western Lumberinan 

 who reported that "extensive and valuable forests of 

 yellow pine in the Southern States are destroyed by a 

 worm commonly called here a ' sawyer,' or flat head." 

 White pine trees are also much beset by the " wood 

 engraver" bark beetle {Xyleborus xylographns, Fitch), so 

 called because it makes beautifully regular and artistic 

 furrows on the surface of the wood under the bark. It 

 is the most common, and probably the most pernicious, 

 of all the insects that infest the forests of white pine in 

 New York State, and of yellow pine in the States south 

 of New York. 



A weevil, the white pine weevil {Pissodes strobi), fre- 

 quently spoils the finest white pines in parts of America 

 by placing numerous eggs in the bark of the topmost 

 shoots of fir trees ; the larvie from these make mines in 

 the wood and pith, causing the shoots to wither and die, 

 thereby occasioning a fork, or crook, at this point. This 

 is a very small insect, not three-quarters of an inch long, 

 and the larvse are not half an inch in length. 



There is a mighty army of caterpillars of various moths 

 described in this Report, which devour the foliage of trees 

 of all kinds in American forests and gardens. Several 

 species of Clisiocampa and Gasteropacha, of the Bomby- 

 cidse, assail oak, willows, ash, chestnut, apple, and pear 

 trees. These are termed " tent" caterpillars, as they live 

 in webs of a tent-like form, as the Clisiocampa Neustria, 

 or lackey moth, in Europe. But the most voracious of 

 caterpillars are the " fall web worms " of the moth 

 Hyphatttria cunea, Drury. For instance, in 1886, the 

 . NO. I 132, VOL. 44] 



city of Washington, as well as its vicinity, was entirely 

 overrun by them. All vegetation, except that not agree- 

 able to their tastes, suffered greatly. Fine rows of shade 

 trees, which grace the streets and avenues, were leafless 

 in midsummer, and covered with hairy worms. The 

 pavements were strewn with moultings of the caterpillars 

 and their webs, which were blown about unpleasantly by 

 the wind. 



Because they are hairy they have comparatively few 

 enemies, among birds at all events. The " English 

 sparrow." fast becoming as great a nuisance in the United 

 States as the rabbit in Australasia, will not look at them, 

 and has driven away by its pugnacity many birds that 

 would eat them. Fortunately there are insect enemies 

 which prey upon them, as the Ma7itis Carolina, or " rear 

 horse," an extraordinary insect of the same family as the 

 "praying" mantis, and the "wheel bug" {Prionidus 

 cristatus). Several parasitic insects also greatly check 

 the spread of this moth. One fly, Telenomus bijidus, 

 Riley, lays its egg within the tiny egg of the moth, in 

 which all the transformations of the fly take place, and 

 its food and lodging are found. In due time, having 

 cleared out the egg, the fly emerges. 



Mr. Bates, in his graphic account of tropical insects, 

 has pictured many that are made to closely resemble 

 their surroundings, for their preservation and other 

 purposes. In his well-known paper on mimicry, he 

 alludes to the insects known as Phasmidae, or " spectre" 

 insects, as especially typical of this adaptation to cir- 

 cumstances, preserved and augmented, as Darwin says, 

 " through ordinary selection for the sake of protection." 

 Mr, Wallace brings forward the Phasmidae as striking 

 instances of mimicry, remarking that " it is often the 

 females alone that so strikingly resemble leaves, while 

 the males show only a rude approximation." 



Species of this family of Phasmidae are mischievous to 

 trees in America, principally the oak and the hickory. The 

 chief of these is the Diapherotnerafemorata, Say., popularly 

 called "walking-stick," "walking -leaves," "stick-bug," 

 " spectre," " prairie alligator," " devil's horse." This in- 

 sect, especially the female, is so like the twigs of trees in 

 colour and appearance, that it is difficult to discover it. It 

 has a habit, too, of stretching out the front legs and feelers, 

 greatly enhancing this re semblance. While the vegetation 

 is green the " walking-sticks " are green ; when the foliage 

 changes in the autumn they also change colour; and 

 when the trees are bare of leaves they closely resemble 

 the twigs on which they rest. The eggs are dropped 

 upon the ground from whatever height the females may 

 be, "and, during the latter part of autumn, where the 

 insects are common, one hears a constant pattering, not 

 unlike drops of rain, that results from the abundant 

 dropping of these eggs, which in places lie so thick 

 among and under the dead leaves that they may be 

 scraped up in great quantities." Prof. Riley adds, with 

 regard to these singular creatures and their wonderful 

 resemblance to the oak vegetation upon which they 

 occur, " one cannot help noticing still further resem- 

 blances. They are born with the bursting of the buds in 

 the spring ; they drop their eggs as the trees drop their 

 seeds, and they commence to fall and perish with the 

 leaves, the later ones persisting, like the last leaves, till 

 I the frost cuts them off." 



