248 FIFTH REPORT OF THE ENTOMOLOGICAL COMMISSION. 



they were more local, and almost entirely confined to certain trees, and mainly so to 

 the white poplar and the cottonwood. Along the Baltimore and Potomac Railroad 

 tracks these trees were defoliated as far as 5 miles from the Capitol. In George- 

 town the caterpillars were equally noxious, but in the adjoining forests but very few 

 webs could be seen. 



The proportionate injury to any given species of tree is to some extent a matter of 

 chance, and in some respects a year of great injury, as 1886, is not a good year to 

 study the preferences of a species, because when hard pressed for food the cater- 

 pillars will feed upon almost any plant, though it is questionable whether they can 

 mature and transform on those which they take to only under the influence of such 

 absolute necessity. Again, the preference shown for particular trees is more the re- 

 sult of the preference of the parent moth than of its progeny in a case of so general a 

 feeder as the Fall Web-worm. We had a very good illustration of this in Atlantic 

 City last autumn. The caterpillars were exceedingly abundant during autumn along 

 this portion of the Atlantic coast, especially on the trees above named. We studied 

 particularly their ways upon one tree that was totally defoliated by September 11. 

 The bulk of the caterpillars were then just through their last molt, though others 

 were of all ages illustrating different hatchings. There was an instinctive migration 

 of these larvae of all sizes, and the strength of their food habits once acquiied from 

 birth upon a particular tree was well illustrated. At first the worms passed over 

 various adjacent plants, like honeysuckles, roses, etc., the leaves of which they 

 freely devour if hatched upon them, but as the migrating swarm became pressed 

 with hunger they finally fell upon these, and even upon plants like the peach, and 

 ailanthus, which ordinarily are passed over. They would pounce upon any food, 

 and a rotten apple placed in their way was soon literally swarming with them and 

 sucked dry. 



In a general way it may be stated that conifers, grapes, and most herbaceous plants 

 are free from their attacks, and it is very doubtful whether the species can mature 

 upon them. 



The list of plants which follows is arranged according to the relative damage to 

 the foliage in the city of Washington. The three first named are most subject to at- 

 tack, and, in fact, are almost always defoliated. 



Proportionate injury to different plants and shade trees. — The damage done in the 

 city of Washington was exceptional, but so was also the general damage throughout 

 the New England States, if not throughout the country. In New England the 

 greater predilection which the species showed for poplar, cottonwood, and the ranker 

 growing willows was everywhere manifest, and so much was this the case that the 

 destruction of the first brood on these trees would have substantially lessened the 

 damage to other trees. 



Plants marked 1 have lost from 75 to 100 per cent, of their foliage. 



Plants marked 2 have lost from 50 to 45 per cent, of their foliage. 



Plants marked 3 have lost from 25 to 50 per cent, of their foliage. 



Plants marked 4 have lost from to 25 per cent, of their foliage. 



Plants marked with two figures have shown the relative immunity or injury indi- 

 cated by both, the variation being in individual trees. 



1. Negundo aeeroides Mcench. (Box El- 

 der.) 

 1. Popnlus alba L. (European White 



Poplar. ) 

 1. Populus monilifera Alton. (Cotton- 

 wood.) 

 1-2. Populus balsamifera L. (Balsam 



Poplar. ) 

 1-2. Populus tremuloidea Mich'x. (Amer- 

 can Aspen.) 



1-2. Fraxinus americana L. (White Ash. ) 



1-2. Fraxinus excelsior L. (European 

 Ash.) 



1-2. Samhucus canadensis L. (Elder.) 



1-2. Pj/rws species. (Cultivated Pear and 

 Apple.) 



1-2. Prunus avium and cerasus L. (Cher- 

 ries.) 



1-4. Syringa vulgaris Li. (Lilac.) 



1-4. Ilex spec. (Holly.) 



