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Dobson and Its Family — Part 1

(Family Sialidae.)

To this group belong the so-called alder flies, fish flies and hellgrammites; in fact, some of them have many popular names. They have four broad wings, of which the hind ones are wide at the base and capable of being folded behind. The wings have numerous veins, both longitudinal and transverse, forming irregular cells. There is a very complete metamorphosis, the larva having strong-toothed jaws and the pupa being quiescent. It is a small family, with only a few genera, but some of the species are so striking in appearance, so interesting in habits, that the group deserves really more extended mention than can be given it here. All of the forms are aquatic or subaquatic in their earlier stages.

Of the typical genus Sialis we have only two species. They comprise the smaller individuals of the family, and frequent vegetation about the banks of streams. Very many eggs are laid by a single female on the vegetation overhanging streams, from two to three thousand being contained in a single egg mass.

Most of our species belong to the genus Chauliodes, of which the so-called comb-horned fish-fly (Chauliodes pectinicornis L.) is the commonest form throughout the United States east of the Rocky Mountains. The eggs do not seem to be known, but the larvae are found in the water crawling along weeds and upon the bottom. They are carnivorous, and feed upon other aquatic insects, and when ready to transform to pupae crawl out upon the bank, and are then found in cavities under stones or even under the bark of trees. The adult insect has a wing spread of three and one-half inches, and is a striking looking creature. Chauliodes lunatus is a large and handsome species with brown wings banded with white. The difference in size between its males and females is very striking.

Needham says that the larvae of Sialis infumata live in trashy places filled with aquatic plants in the border of streams and ponds. They clamber through fallen vegetation with great agility, and push their way readily through sediment fallen upon the bottom. In an aquarium, and probably outside, the long tail is intermittently lashed up and down. This causes a swirl in the water, which is doubtless useful in bringing a fresh supply of well-aerated water into contact with the lateral filaments. When the larvae are full grown they burrow into the soil for several inches and become pupae without making a cocoon. The adult fly emerges after two or three weeks.

The eggs of Chauliodes have been found by Needham in the Adirondack region of New York to be very generally parasitized by a very minute egg parasite, a chalcis fly, more than seventy per cent. of the eggs being destroyed in this way.

The most familiar American example of this group is the so-called hellgrammite fly, some account of which is given in the following paragraphs.

Life History of the Dobson

(Corydalis comuta L.)

This is one of the most striking and most curious of insects which occur in North America. Its transformations were first described in part by S. S. Haldeman in 1848. It is interesting to note that at that time, although the insect was well known to most people in the localities where it was found, Dr. Haldeman was never able to discover that it had a vernacular name either in English or German among the so-called Pennsylvania Dutch. Surely this defect must have been speedily remedied, since the great four-winged fly with its enormous jaws is now generally known as the hellgrammite. while its great, strong, biting, wriggling larvae are familiar to fishermen in many parts of the United States as Dobsons, or crawlers. In fact, it is likely that not one of our insects has so many vernacular names at the present time. In 1889 Professor W. W. Bailey, of Brown University, collected the names in use in Rhode Island alone for this insect, and they are sufficiently interesting to be repeated. They are: Dobsons, crawlers, amly, conniption bugs, clipper, water grampus, goggle goy, bogart, crock, hell devils, flip-flaps, alligators, Ho Jack, snake-doctor, dragon and hell-diver.

It will be very easy to infer from these names alone that the insect is a very extraordinary one and somewhat terrifying in its appearance.

The adult is a large creature, having a wing spread of more than four inches, and possessed, in the female, of powerful biting jaws, with which it can give a severe pinch to the skin of the person who handles it carelessly. With the male there is a curious modification of the jaws. They are extended into long, curved, piercing organs, which cross when at rest, and which are fully an inch in length. These jaws make the male look particularly dangerous, but, fortunately, they do not function as jaws, and are simply used for the purpose of holding the female during marital caresses.