The Phryganidæ, or Caddis Flies, are known by their larvæ, of which anglers make great use. Réaumur classed them as aquatic moths. The soft and delicate body of the larvæ is protected by a case, to which they cling by two hooks, placed at the extremity of their abdomen. They are called by different names in allusion to their habits; as, for instance, case worms, from their living in a case covered with little bits of wood or sand, which they draw after them as they go. Their scientific name, Phryganea, signifies fagot. [120] The Phryganeæ, in the adult state, very much resemble moths. They approach them in having rudimentary mouths, and wings without articulations, but furnished with small hairs, analogous to the scales of Lepidoptera. They may be said to form a sort of connection between the Lepidoptera and Neuroptera. They have been called Mouches papilionacées, or Papilionaceous Flies. The eggs laid by the female Phryganea are enclosed in gelatinous capsules, which swell in the water and attach themselves to stones, &c. The larva has the appearance of a little worm without feet. It is soon hatched, and resembles at first a little black line, and may be easily reared in an aquarium. The operation of making the silky case which it draws after it, and which protects its abdomen, may then be observed. When it is disturbed, it retreats entirely within its case. The interior is smooth, and lined with mud; on the exterior it is fortified with stones, &c.
Fig. 418.
Regular cases of a Phryganea.
The Phryganea rhombica (Figs. [415], [416], [417]) furnishes its case with bits of wood or grass, arranged as shown in [Fig. 418]. Some species arrange these bits of wood and glass in spiral, others in parallel series. The Phryganea flavicornis covers its dwelling with little shells. "These kinds of dress," says Réaumur, "are very pretty, but they are also excessively singular. A savage who, instead of being covered with furs, should be covered with musk rats, moles, or other entire animals, would have on an extraordinary costume; this is in some sort the case with our larvæ." Other Phryganeæ employ for constructing the case which serves them as a dwelling sand and small pebbles; each species always employing the same materials, unless they are entirely deprived of these and obliged to employ others. These cases protect the larvæ against the voracity of their enemies. The larvæ have a scaly head; and the three first rings of their body are harder than the rest. They live in water, and breathe by means of branchious sacs, arranged on the abdomen in soft and flexible tufts. They eat everything that is presented to them: leaves, and even insects and the larvæ of their own kind. The pupæ are motionless. They stay about a fortnight in their case, the orifice of which is closed by gratings of silk, then break through the gratings, and leave their prison. In this state ([Fig. 419]) they swim on the water until they meet with an object to which they can attach them selves, and so get out. Then they swell till they crack their skin over the back, and the perfect insect emerges.
The Phryganea pilosa ([Fig. 420]) is of a yellowish grey, with hairy wings, little adapted for flying. These insects do not eat, and never leave the neighbourhood of the water. During the day they rest on flowers, on walls, or on the trunks of trees, their wings folded back, and their antennæ together. In the evening they fly in dense swarms over streams and ponds. They are attracted by light, as are many nocturnal insects; and are sometimes found in great numbers on the lamps on the quays in Paris.
| Fig. 419.—Pupa of Phryganea pilosa, magnified. | Fig. 420.—Phryganea pilosa. |
The Hydropsyches ([Fig. 421]) and Rhyacophili ([Fig. 422]) are small insects which resemble the Phryganeæ very closely. Their larvæ have, for the purposes of respiration, some gills, others retractile tubes. They construct for themselves fixed places of shelter, more or less imperfect, at the bottom of the water, and against large stones, which they leave occasionally for a few moments. Sometimes these cases contain several larvæ. [Fig. 421] represents the various states of a Hydropsyche; the larva is seen on the left, the pupa on the right, the winged insect in the middle. Two of the insect's tents, or places of shelter, are represented below. [Fig. 422] shows the different states of Rhyacophilus vulgatus, larva, cocoon, pupa, and imago. The genus Rhyacophilus has this peculiarity, that the larva spins itself a cocoon in the interior of its dwelling before changing into a pupa.
