42 



with tlieir jaws buried in the bodies of the Hyphantria larvae just back 

 of the head. 



June 27. the preseuee of this savage and persistent enemy seemed 

 to utterly u demoralize" the web worms, causing them to repeatedly 

 •'break up housekeeping 75 and seek new locations, separating into 

 smaller and smaller groups in the instinctive search for safety. But 

 the attempt is vain: for no soouer are they established than Plochionus 

 is on the trail, and is uot long in discovering their whereabouts and 

 biting into them whenever it is hungry. 



By the end of June the colonies on both trees, though not nearly full- 

 grown and greatly reduced in numbers, had dispersed, the gregarious 

 instinct having evidently been lost much sooner than usual. A few 

 Plochionus larvae about one-half size were to be seen in the deserted 

 webs for a day or two after the web worms had disappeared, after which 

 they. too. departed, and I presume descended to the ground, where they 

 preyed upon such larva? as could be found there. A few were placed 

 in a rearing jar and supplied with Spilosoma. Orgyia and other hairy 

 larva?, but these were not attacked, nor was I able at the time to find 

 any other species upon which they would feed, and all perished without 

 completing their development. 



The second brood of Hyphantria. which with us has always been 

 most numerous and injurious, was very sparsely represented in this 

 locality. Upon my return from the East I made diligent search in 

 Kirkwood and vicinity for the remains of webs or other evidence of the 

 worms, but could find very few. To my mind there is no question 

 that this happy immunity is due primarily to the agency of the little 

 Carabid. whieh has in some way suddenly acquired the habit of prey- 

 ing upon them. 



TTropoda americana. — About the middle of July I received froin Mr. 

 F. M. Webster a few specimens of the Striped Cucumber Beetle (Dia- 

 brotica vittata), thickly infested with the above-named large brown 

 mite, with the request that I attempt to colonize it on the same or allied 

 species of beetles here. Just at that season I could find but very few 

 examples of D. vittata, but as D. 12-pu ncta ta was abundant I hoped the 

 mites would accept the latter as a substitute. In this I was disappointed, 

 the parasites refusing to leave their original hosts. After a few days 

 two or three specimens of vittata and several each of Colaspis prce- 

 texta, C. tristis, Lema trilineata, and Doryphora 10-lineata were intro- 

 duced into the jar and each supplied with its preferred food. The jar — a 

 -large one of clear glass — was kept on my desk under constant observa- 

 tion, and in two days I noticed a few of the mites on each species of 

 Colaspis, with a very evident preference for the pretty blue tristis. In the 

 course of a week all the specimens of the latter were thickly covered and 

 much weakened, while only a few were found on preetexta and none at 

 all on any of the other species, not even on the fresh specimens of their 

 original host. In accordance with a suggestion, the attempt was made 



