272 OHIO EXPERIMENT STATION: BULLETIN 332 



in appearance, are in reality almost harmless. A cluster of the 

 caterpillars is shown in Plate XLIII, Fig. 1. The pupa is about an 

 inch long, purplish-gray in color and is suspended by the rear part 

 of the body. 



Life history and habits. The insect passes the winter in the 

 adult stage within the shelter of a hollow tree or some other con- 

 venient place. With the first warm days of spring the butterflies 

 emerge and may be seen flying about woody places. After the 

 appearance of the foliage the eggs are deposited and the young 

 caterpillars soon hatch and begin feeding. They are highly gre- 

 garious, spinning a slight silken thread as they feed. When nearly 

 mature they lose their gregarious habits to a certain extent ; never- 

 theless it is maintained sufficiently to designate as one of the char- 

 acteristics of the species that of defoliating branches and parts of 

 trees rather than generally distributed injury over the whole tree. 



Pupation occurs after the caterpillar has suspended itself from 

 some nearby object. There are at least two broods per season and 

 perhaps a third. The insects and particularly the caterpillars are 

 much more prevalent during early and midsummer than during 

 late summer and fall. 



Nature of work. This is both a woodland and city-dwelling 

 species sometimes reaching sufficient numbers to be classed as a 

 serious pest. While no such instance has come under the observa- 

 tion of the writer, several have been reported from New York and 

 New England. However, instances of partial defoliation by the 

 larvae are not uncommon in this State. 



Food plants. While elm and willow are the preferred food 

 plants the insect has been observed upon poplars, birch, hackberry 

 and linden. 



Distribution. This species, according to Doctor Britton, is 

 distributed throughout the temperate regions of the globe. 



Natural enemies. According to Doctor Felt (28) the follow- 

 ing natural agencies prey upon this species : Chalcids : Telenomus 

 graptae How., Pteromalus fuscipes Prov., P. vanessae How., P. 

 puparum Linn, and Derostenus antiopae Pack. Coleoptera: Cal- 

 osoma scrutator Fabr. Pentatomids: Apateticus placidus Uhler 

 and A. serieventris Uhler. Birds: black and yellow-billed cuckoos. 



Several species of Ichneumons are reported from Europe. 



In addition to the foregoing, Viereck et. al. (35) report Hop- 

 lismenus morulus Say and Pteromalus puparum var. vanessae 

 Harris. 



