The genera Corydalis and Chauliodes form a group distinct from Sialis, and are totally different in appearance, being gigantic Insects, sometimes with the mandibles of the male enormously elongated (Fig. 290). The species of Corydalis are called in North America Hellgrammites; Riley has described and figured the metamorphosis of C. cornutus,[[373]] the life-history being very similar to that of our little Sialis. A mass consisting of two or three thousand eggs is formed by the female, and the young larva has long filaments at the sides of the body like Sialis. These in the later larval life are comparatively shorter, but the Insect is then provided with another set of gills in the form of spongy masses on the under-side of the body. Riley, however, considers that these organs serve the purpose of attachment rather than of respiration. The larvae are known to the Mississippi fishermen as crawlers, and are greatly esteemed as bait.
The Raphidiides or snake-flies form the second tribe of Sialidae. There are only two genera, Raphidia and Inocellia, peculiar to the Palaearctic and Nearctic regions. The perfect Insects are chiefly remarkable for the elongation of the prothorax and back of the head to form a long neck, and for the existence in the female of an elongate exserted ovipositor. The species are rather numerous, and have been recently monographed by Albarda.[[374]] The three or four British species of the genus are all rare Insects, and occur only in wooded regions.
The Raphidiides, like the Sialides, have a carnivorous larva, which, however, is terrestrial in habits, feeding, it would appear, chiefly on Insects that harbour in old timber. The snake-fly larvae (Fig. 292) are very ingenious in their manner of escaping, which is done by an extremely rapid wriggling backwards. They are capable of undergoing very prolonged fasts, and then alter in form a good deal, becoming shorter and more shrivelled; Fig. 292 is taken from a specimen that had been fasting for several weeks. They are excessively voracious, and hunt after the fashion of beasts of prey; their habits have been described by Stein,[[375]] who states that he kept a larva from August to the end of May of the following year without food; it then died in a shrivelled-up state. The larva of the snake-fly changes to a pupa that is remarkably intermediate in form between the perfect Insect and the larva; the eyes, legs, wing-pads, and ovipositor being but little different from those of the imago, while the general form is that of the larva, and the peculiar elongation of the neck of the imago is absent. This pupa differs from that of Sialis in the important particular that before undergoing its final ecdysis it regains its activity and is able to run about.
Fig. 292.—Raphidia notata, larva. New Forest.
The internal anatomy of Raphidia has been treated by Loew,[[376]] and is of a very remarkable character; we can here only mention that the salivary glands consist of a pair of extremely elongate tubes, that there is a very definite paunch attached as an appendage to one side of the crop, and that the most peculiar character consists of the fact that, according to Loew, four of the six Malpighian tubes have not a free extremity, being attached at each end so as to form elongate loops; the mesenteron is very complex in character.
A considerable number of fossil remains from both Tertiary and Mesozoic strata are referred to Sialidae; and a larval form from the red sandstone of Connecticut has been considered by Scudder to be a Sialid, and named Mormolucoides articulatus, but the correctness of this determination is very doubtful (Fig. 293). These fossils are, however, of special interest as being the most ancient Insect larvae yet brought to light. A still older fossil, from the Carboniferous strata of Illinois called Miamia bronsoni, is considered by Scudder to have several points of resemblance to Sialidae.
Fig. 293.—Mormolucoides articulatus, larva. Trias of Connecticut. (After Scudder.)
Fam. IX. Panorpidae—Scorpion-flies.