134 CRABS AND INSECTS. 
Butterflies (Papilionide).—General Characteristics, 
The butterflies are day-flying Lepidoptera, and distin- 
guished from the moths by their knobbed antenne. 
Vanessa.—In this genus (Fig. 169) the wings are richly 
marked. The larva is cylindrical, and covered with stout, 
long-branching spines. The V. antiopa is one of the com- 
monest forms, and famous for its habits of hibernation. 
Fic. 169. —Metamorphosis of the peacock butterfly (Vanessa Io). 
Sulphur-Butterflies (Co/as).*—In this family the 
wings are rounded, and form a gutter for the reception of 
the abdomen. They are the commonest butterflies we have. 
*In some countries they flock upon certain trees, completely 
covering them, so that in the sun they appear to have a golden hue. 
Darwin met a vast cloud of them, ten miles at sea, off the Bay of San 
Blas, and as far as could be seen the swarm extended. Sir Emerson 
Tennent observed a flock in India that was several days in passing a 
given point at a high rate of speed. Sir Robert Schomburgh observed 
a cloud of another genus crossing the Essequibo River, South America, 
that was nine miles wide, and was nine hours in passing the stream. 
