BUTTERFLIES OF THE DISTEICT OF COLUMBIA 209 



common pigweed {Ghenopodium albv/m), but also on other plants 

 belonging to the family Chenopodiaceae, on species of the closely 

 allied Amaranthaceae, and occasionally on species of other families. 



By bending up the two edges of a leaf and fastening them to- 

 gether with silk, or occasionally by binding two leaves together, 

 the caterpillars fashion for themselves a shelter in the form of a 

 hollow cylinder in which they live. These shelters are very easily 

 found, and when they are opened the caterpillars are readily recog- 

 nized by the pale green color, swollen dark-brown head, and con- 

 stricted neck with a narrow dark brown collar. 



In autumn the caterpillars simply become dormant within these 

 shelters, which they reinforce and seal with silk. With the collapse 

 of the food plant the shelters come to lie upon the ground. 



Winter is passed as a fully fed caterpillar, which in spring 

 changes to a pupa without leaving the flimsy structure formed in 

 autumn. If the food plant withers prematurely the caterpillars 

 will sometimes wander away and form a flimsy cocoon elsewhere. 



Remarks. — The presence of this species in any locality is most 

 easily demonstrated by finding the caterpillars. Tliey are particu- 

 larly numerous and easy to discover in the last half of October. 



Genus THANAOS Boisduval 



The butterflies of the genus Thanaos are remarkable for their 

 close superficial resemblance to one another, which makes them very 

 difficult for anyone not especially familiar with them to identify. 

 Specific determinations, therefore, should always be checked by an 

 authority on the group, or at least by someone thoroughly ac- 

 quainted with the local species. 



We need much more information than we have on the early stages 

 of nearly all our species. Though they are not difficult to raise, 

 the slow growth of the caterpillars makes raising them a rather 

 tedious process. 



All the species in this region, so far as known, spend the winter 

 as fully grown caterpillars, changing to pupae without eating early 

 in spring. 



These are among the very earliest of our butterflies to appear, 

 and are especially to be found along roads through woods growing 

 in hilly country, about exposed rocks in woods, and about clearings. 

 Some prefer areas covered with scattered scrub oak, and some are 

 more or less common in open fields near woods. The individuals of 

 the later broods are much more likely to be found in open country 

 than are those of the spring brood. 



Some species have but a single brood, some have a partial second 

 brood, and one of ours has three broods. 



