Mayflies are called ephemerids, For though as nymphs they may Live for a year, when they are grown They live but for a day. We find the nymphs in ponds and rills And know them by their leaf-like gills.
YOUNG mayflies can be found in almost any pond or stream. The common ones are recognized by their seven pairs of gills which look like little leaves attached to each side of the abdomen. Although these gills appear to be quite different from those of a caddis fly larva, they are used for respiration in the same way. Oxygen from the water enters the gills and is carried through the young mayfly's body in fine, branched air-tubes.
You can see the gills plainly in the photograph which illustrates this chapter. You can see them clearly, too, on a live mayfly, for they move continuously when he is in the water.
Many young mayflies swim gracefully in the calm water of ponds; others burrow like tiny moles into the soft mud. Several kinds prefer the rough, rapid waters of brooks and streams, and are found clinging to the under sides of rocks in swiftly flowing waters.
A young caddis fly is called a larva, but a young mayfly is called a nymph. Each is a young insect which has developed from an egg, and which is in the feeding and growing period of its life. One difference between them is that the caddis fly larva will become a pupa before it develops into an adult, but the mayfly nymph will not. The life of the caddis fly can be divided into four stages: egg, larva, pupa, adult. In the lives of many other insects there are only three distinct stages: egg, nymph, adult. Insects like the caddis fly, which have a complete change of
form as they develop, are said to undergo complete metamorphosis. The change which mayflies and stoneflies undergo is described as incomplete metamorphosis.
Mayfly nymphs which live in swiftly flowing water have broad, flat bodies which help them cling to rocks. Their heads and legs are flattened, also, and they may have suction disks on the under sides of their bodies. Mayfly nymphs that live in the quiet water of lakes or ponds have narrower bodies, and they swim about more. Instead of hiding in the dark, they crawl over water plants and swim through the water. Both kinds have two or three long tails and one claw on the tip of each foot.