244 Fiftieth Report on the State Museum 



tree is attributed to unusual dry weather, to the impervious street pave- 

 ments of many of our cities, to defective gaspipes, or some other cause,, 

 while the true agents of the mischief continue their destructive work 

 unknown and undisturbed. Throughout the entire State, and beyond its 

 limits, the American elm has for a number of years been suffering from 

 the ravages of this hidden and insidious enemy, the trees dying one by 

 one from a cause, not apparent, and known to but a few. 



Character and Extent of Injury. 



The larvse or grubs of this insect work in the inner bark and sap-wood 

 of the trunk, — the attack apparently commencing not far above the 

 ground and gradually extending upward. Most of the burrows are in 

 the inner bark, although a few occur at the depth of an inch or more. 

 When the grubs are numerous, their broad flat burrows, varying from one- 

 tenth to two-tenths of an inch in width and about one-tenth of an inch 

 deep, so reticulate and run into one another as effectually to girdle trunks 

 of trees two or three feet in diameter, when, with the circulation arrested, 

 the death of the tree inevitably follows. The bark is frequently so badly 

 infested that in old trees it can be detached in large sheets. The work 

 of this pest is shown in figures 4, 5, of plate VII. 



As early as 1847 and 1848, Dr. Harris had noticed that this insect was 



very injurious to the elms on Boston Common. He wrote as follows : 



The trees were found to have suffered terribly from the ravages of 

 these insects. Several of them had already been cut down, as past 

 recovery; others were in a dying state, and nearly all of them were more 

 or less affected with disease or premature decay. Their bark was per- 

 forated, to the height of thirty feet from the ground, with numerous holes 

 through which insects had escaped; and large pieces had become so 

 loose by the undermining of the grubs as to yield to slight efforts, and 

 come olif in flakes. The inner bark was filled with the burrows of the 

 grubs, great numbers of which, in various stages of growth, together with 

 some in the pupa state, were found therein; and even the surface of the 

 wood, in many cases, was furrowed with their irregular tracks. 



Most of the wood and bark borers are partial to diseased and dying 



trees, as is well known to many. An enfeebled condition of the trees 



from their age or some other cause, may account for the severity of the 



attack noted above. Dr. Fitch, in his Fifth Report, records that the 



larvae of this insect infested the remaining bark of all of the slippery elms, 



Ulnius fulva, in his vicinity, after the best of it had been stripped off for 



medicinal purposes. The operations of this insect appear to be notorious, 



for it has been characterized by Dr. Packard as the most destructive 



borer in the Northern and Eastern States, often killing trees by the 



wholesale. In 1884, its ravages were so serious that Prof. Forbes wrote : 



