LEPIDOPTERA. 271 



seem to have a repelling power, and prevent the water from 

 wettino- their skins, so that they float on the surface, and are 

 often carried by the waves to distant places, where they are 

 thrown on shore, and left in winrows with the wash of the 

 sea. After a little time most of them recover from their half- 

 drowned condition, and begin their depredations anew. In 

 this way these insects seem to have spread from the places 

 where they first appeared to others at a considerable distance. 

 From the marshes about Cambridge they were once, it is said, 

 driven in great numbers, by a high tide and strong wind, upon 

 Boston neck, near to Roxbury line. Thence they seem to have 

 migrated to the eastern side of the neck, and, following the 

 marshes to South Boston and Dorchester, they have spread in 

 the course of time to those which border upon Neponset river 

 and Quincy. How far they have extended north of Boston I 

 have not been able to ascertain ; but I believe that they are 

 occasionally found on all the marshes of Chelsea, Saugus, and 

 Lynn. Although these insects do not seem ever entirely to 

 have disappeared from places where they have once established 

 themselves, they do not prevail every year in the same over- 

 whelming swarms ; but their numbers are increased or lessened 

 at irregular periods, from causes which are not well understood. 

 These caterpillars are produced from eggs, which are laid by 

 the moths on the grass of the marshes about the middle of 

 June, and are hatched in seven or eight days afterwards, and 

 the number of eggs deposited by a single female is, on an 

 average, about eight hundred. The moths themselves vary 

 in color. In the males, the thorax and upper side of the fore 

 wings are generally white, the latter spotted with black ; the 

 hind wings and abdomen, except the tail, deep ochre-yellow, 

 the former with a few black spots near the hind margin, and 

 the abdomen with a row of six black spots on the top of the 

 back, two rows on the sides, and one on the belly; the under 

 side of all the wings and the thighs are deep yellow. It ex- 

 pands from one inch and seven eighths to two inches and a 

 quarter. The female differs from the male either in having the 

 hind wings white, instead of ochre-yellow, or in having all the 

 wings ashen gray with the usual black spots. It expands two 



