_Colias philodice_, the Common Yellow, is the butterfly seen swarming about roadside mud-puddles in August and September. The wings are lemon color with black borders, and in the female the borders are usually broken by several small yellow spots. The yellow or reddish eggs are laid upon various kinds of clover; the slender green caterpillar is exactly the color of the leaves; the chrysalis is usually pale green also. This butterfly is found from New England to Florida, and as far west as the Rocky Mountains. _Terias lisa_ is another yellow butterfly, much smaller than Colias philodice, rarely expanding more than an inch and a quarter. The wings are lemon yellow with black borders, subject to many minor variations. The caterpillar feeds on clover, but the early stages of this species have never been thoroughly studied, despite the fact that the butterfly is common from the New England states to the Rockies. _Terias mexicana_, the Mexican Yellow, is larger than _Terias lisa_, and somewhat paler in color. The black borders or the fore wings are very wide and indented, and the hind wings are pointed. Very little is known of its early stages. It is common in Texas, Arizona, and Southern California, and often strays much farther north. I have myself taken a number of specimens in Kansas. THE PAPILIONINAE This is the subfamily of the true swallowtails, the largest and most distinctive of American butterflies. The hind wings are prolonged into two tail-like projections, and are characterized, by the absence of the internal vein. The caterpillars are all provided with peculiar V-shaped scent-organs called _osmateria_; these organs are thrust out just back of the head when the insect is disturbed, and give off an offensive odor, supposed to discomfit birds and other enemies. _Papilio troilus_, the Green-clouded Swallowtail, is velvety black with a row of yellow spots along the margin of the fore wings. The marginal spots on the hind wing are pale green, and the whole outer half of the hind wing is clouded with the same greenish tinge. The female deposits her eggs on sassafras and spicebush leaves; the caterpillar is lead-colored or greenish, with a swollen thorax bearing two large eye-spots, and lives in a nest made of a folded leaf. _Papilio troilus_ is common throughout the Atlantic States and in the Mississippi Valley.