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Dobson and Its Family — Part 2

The female lays her eggs in white, chalky-looking masses about the size of a nickel five-cent piece. These masses are somewhat convex, and contain about three thousand very small eggs set on end. They are deposited on the leaves of trees overhanging the water, or on rocks, or the piers of bridges or similar places where the larvae can readily drop into the stream or pond. Sometimes they are so abundant as to make the rocks look as though someone had splashed whitewash upon them profusely with a brush.

The young on hatching drop immediately into the water, descend to the bottom, and during the entire larval life, which lasts two years and eleven months, feed upon other aquatic insects, especially the early stages of the May-flies and stone-flies. They hide under stones in swift-running currents, and possess at the anal end of the body two strong tubercles, each provided with two curved claws, with which they hold firmly to one object or another. They breathe through several pairs of tufts of breathing filaments situated just beneath each side of the abdomen. They also, when they approach full growth, have spiracles, which are closed, however, until the creature is ready to emerge from the water. The number of molts is not recorded. When full grown (two years and eleven months after its birth), the larva leaves the water and crawls about seeking a suitable place for pupation. It does not travel very far, but it crawls energetically while it is about it, curiously enough, climbing trees occasionally, and on several occasions in Illinois they fell down the chimney of a house occupied by the man who kept the toll bridge over the Rock River. They travel on land only by night, hiding under some stone or log during the day, and it is under stones and logs that they finally pupate.

The larva in color is dark slate-gray, and is remarkably thick-skinned and tough. This fact adds to their value as bait, since one will last a long while. The pupa, however, is light yellow in color, and transforms to the adult fly in about a month. Full grown larvae begin to emerge from the water in May, and the adults are seen flying a month later.

In rapid, rock-bottomed streams, where these insects abound, the method of catching them is to wade in the streams with a net and lift up the stones in advance, catching the larvae in the net as they float down with the current.

They bear at the sides of the body, in addition to the respiratory tufts mentioned above, tow long filaments on each side, which are furnished with hairs, and may be of some service in swimming. Possibly, also, with the very young larvae they have a respiratory function. When the larvae become large, however, dissection shows that the tracheae contained in these filaments are insignificant, whereas each element of the branchial tufts possesses a strong branched trachea.

Mr. R. S. Clifton has found an interesting little dark-colored beetle (Anthicus haldemanni) along the Potomac River, feeding upon the egg masses of the hellgrammite fly. The beetle was found to lay its eggs upon the egg masses and its larvae were found destroying the eggs. Sometimes as many as a dozen of the larvae were found in a single egg mass.