This family is of large extent, and includes at present so great a variety of forms that it is really almost impossible to frame a definition that will apply to all. The unusual situation of the ocelli and the peculiar second joint of the antennae must at present be taken as the best diagnostic characters: occasionally a third ocellus is present. Some of the Fulgoridae are amongst the largest Insects, others are quite small. The family includes the so-called Lantern-flies, in which the front of the head forms a huge misshapen proboscis that was formerly believed to be luminous. Many of the species are of brilliant or beautiful coloration. A great many—and of very different kinds—have the curious power of excreting large quantities of a white, flocculent wax. This is exhibited by our little British Insects of the genus Cixius, and in some of the exotic forms is carried to an extent that becomes a biological puzzle. The Tropical American genus Phenax may be cited as an example; being about an inch long it flies about with a large mass of this waxy substance twice as long as itself; indeed, in the Mexican P. auricoma, the waxy processes are four or five inches long. This wax forms a favourite food of certain kinds of Lepidoptera, and two or three larvae of a maggot-like nature may frequently be found concealed in the wax of the live Fulgorids; this has been recorded by Westwood as occurring in India; and Champion has observed it in the New World.[[506]] The wax of Fulgorids is used by the Chinese for candles and other purposes; and this white Insect-wax is said to be much esteemed in India. Very curious chemical substances have been obtained from it, but its importance in the economy of the Insects that produce it is quite obscure. We have about seventy species of Fulgoridae in Britain. They belong to the subfamilies Tettigometrides, Issides, Cixiides, and Delphacides, which by many authors are treated as separate families. The exotic subfamily Flatides is highly peculiar. In some of its members the head is very different from that of the ordinary forms, being narrow, and the vertex and front forming a continuous curve. Some of these Insects are remarkably like butterflies or moths (e.g. the African Ityraea nigrocincta and the species of the genus Pochazia), but the young are totally unlike the old, the posterior part of the body bearing a large bush of curled, waxy projections, several times the size of the rest of the body.
Fig. 283—A, B, Heteronotus trinodosus. A, Male seen from above; B, profile of female; a, terminal part of pronotum; b, terminal part of abdomen: C, front view of head and pronotum of Cyphonia clavata. Both species from Central America. (From Biol. Centr. Amer. Rhynch. Homopt. II.)
Fam. 3. Membracidae.—Prothorax prolonged backwards into a hood or processes of diverse forms; antennae inserted in front of the eyes; ocelli two, placed between the two eyes.—This family is of large extent but its members are chiefly tropical, and are specially abundant in America. Although not of large size the Membracidae are unsurpassed for the variety and grotesqueness of their shapes, due to the unusual development of the pronotum. We figure two of these forms (Fig. 283).[[507]] Very little is known about their habits and life-histories. We have only two species of the family in Britain, and these do not afford any ground for supposing that there are any peculiarities in their lives at all commensurate with the oddness of the Insect's structures. Belt has recorded the fact that in Nicaragua the larvae of certain Homoptera were assiduously attended by ants for the sake of a sweet juice excreted by the bugs, but it is by no means clear that these larvae were really those of Membracidae. In North America Ceresa bubalus and C. taurina place their eggs in an extremely neat manner in the woody twigs of trees. The young have but little resemblance to the adults, the great thoracic hood being absent, while on the back there is on each segment a pair of long, sub-erect processes having fringed, or minutely spiny, margins.[[508]]
Fam. 4. Cercopidae.—Ocelli two (occasionally absent) placed on the vertex; antennae placed between the eyes. Thorax not peculiarly formed.—In the characteristic forms of this family the front of the vertex bears a suture, touched on each side by one at right angles to it, or converging to it so as to form a triangle or a sort of embrasure; the hind tibiae have only one to three strong spines. The Cercopidae are much less extraordinary than many of the previously considered families. But some of them have the habit of secreting a large quantity of fluid; and when in the immature stages, certain of them have the art of emitting the liquid in the form of bubbles which accumulate round the Insect and conceal it. These accumulations of fluid are called cuckoo-spits or frog-spits; and the perfect Insects are known as frog-hoppers, their power of leaping being very great. The most abundant of the frog-hoppers in our gardens is Philaenus spumarius, a little Insect of about a quarter of an inch long, obscurely coloured, with more or less definite pale spots; it is so variable in colour that it has received scores of names. Some of the Insects do not use their fluid in this manner, but eject it in the form of drops, and sometimes cast them to a considerable distance. The phenomena known as weeping-trees are due to Cercopidae; some of the species make such copious exudations of this kind that the drops have been compared to a shower of rain. In Madagascar it is said that Ptyelus goudoti exudes so much fluid that five or six dozen larvae would about fill a quart vessel in an hour and a half. The frog-spit is considered by some naturalists to be a protective device; the larvae are, however, a favourite food with certain Hymenoptera, which pick out the larvae from the spits and carry them off to be used as stores of provision for their larvae. In Ceylon the larva of Machaerota guttigera constructs tubes fixed to the twigs of the tulip-tree, and from the tube water is exuded drop by drop. According to Westwood, this Insect is intermediate between Cercopidae and Membracidae.[[509]]
Fam. 5. Jassidae.—Ocelli two, placed just on the front margin of the head (almost in a line with the front of the eyes or more to the front) or on the deflexed frons. Hind tibiae usually with many spines. This vaguely limited family includes a very large number of small or minute Insects, usually of narrow, parallel form, and frequently excessively delicate and fragile. They are often mentioned under the name of Cicadellinae. Ashmead distinguishes two families, Bythoscopidae, in which the ocelli are clearly on the frons or front, and Jassidae, in which they are on the upper edge thereof. Ulopa, Ledra, and a few other exceptional forms, are also by many distinguished as representatives of distinct families. Very little is actually known as to the life-histories of these small and fragile Insects, but it is believed that the eggs are usually deposited in the leaves or stems of plants, and more particularly of grasses. In North America the development of Deltocephalus inimicus, from hatching to assumption of the adult form, has been observed by Webster to occupy about six weeks. As Jassidae are numerous both in species and individuals it is believed that they consume a considerable part of the vegetation of pastures. Osborn has calculated that on an acre of pasture there exist, as a rule, about one million of these hoppers, and he considers they obtain quite as large a share of the food as the Vertebrates feeding with them.
Fam. 6. Psyllidae.—Minute Insects with wings usually transparent, placed in a roof-like manner over the body; with three ocelli, and rather long, thin antennae of eight to ten joints. Tarsi two-jointed.—These small Insects have been studied chiefly in Europe and North America, very little information having yet been obtained as to the exotic forms. They are about the size of Aphidae, but in form and general appearance remind one rather of Cicadidae. The wings are in many cases even more perfectly transparent than they are in many Cicadidae. They are sometimes called springing plant-lice, as their habit of jumping distinguishes them from the Aphidae. Löw has called attention to the remarkable variation in colour they present in conformity with either the age of the individual, the food-plant, the climate, and, more particularly, the season of the year.[[510]] Réaumur long since pointed out that at their ecdyses these Insects go through a remarkable series of changes of colour, and Löw found that this did not take place in the normal manner in the winter generation that hibernates. This has been confirmed by Slingerland in North America in the case of Psylla pyricola,[[511]] which has been introduced there. He finds that there are several generations in the year, and that the hibernating adults differ from the summer adults in size, being nearly one-third larger; in their much darker colouring; and especially in the coloration of the front wings.
Fig. 284—Psylla succincta. x 15. Europe. (After Heeger.) A, larva before first moult. B, larva after third moult. C, adult.
In the earlier stages, Psyllidae differ greatly in appearance from the adult forms; the legs and antennae in the newly hatched larvae are short, and have a less number of joints. In the nymph the shape is very peculiar, the large wing-pads standing out horizontally from the sides of the body, so that the width of the creature is about as great as the length. The period occupied by the development apparently varies according to season. Witlaczil, who has given an account of many details of the anatomy and histology of various Psyllidae,[[512]] considers that there are four larval stages; Heeger's account of Psylla succincta is not quite clear on this point, and Slingerland indicates a stage more than this, the perfect Insect being disclosed as the result of a fifth moult; it is probable that he is correct. In these earlier stages the body bears long hairs called wax-hairs; according to Witlaczil in the young larvae of certain species—Trioza rhamni, e.g.—these are broad and flat, so as to make the body appear studded with oval processes; he states that these hairs change their form during the growth of the individual. Nothing is more remarkable in Psyllidae than the amount of matter they secrete or exude from their bodies; in some species the substance is a "honey-dew," and the nymph may keep itself covered with a drop of it: in other cases it is solid, as shown in Réaumur's figures of P. buxi, where this exudation forms a string several times longer than the body, and attached to it. Another form of exudation is a light downy or waxy matter. Slingerland says that honey-dew was exuded by P. pyricola in such quantities that it "literally rained from the trees upon the vegetation beneath; in cultivating the orchard the back of the horse and the harness often became covered with the sticky substance dropping from the trees. It attracts thousands of ants, bees, and wasps, which feed upon it." The writer last year observed in the New Forest a stunted sloe-bush, about which a large number of Bombi were busily occupied; and examination showed that they were thrusting their proboscides into the curled and deformed leaves, in which were secreted nymphs of a Psylla exuding honey-dew. It must not be assumed that this honey-dew is the excrement of the Insect; this also is known, and is a different substance. Those who have tasted it say that the honey-dew has a clean, good flavour. The source of the honey-dew is not quite certain, but it seems probable that it comes, like the solid matter figured by Réaumur, directly from the alimentary canal, and not from hairs or pores on the body. Psyllidae give rise to definite formations or galls on certain plants; sometimes these Psyllid galls are mere changes in form of a limited part, or parts, of a leaf, giving rise either to crumpling or to growth of a portion in one direction only, so that on one surface of the leaf a swelling is formed, and on the opposite side a more or less deep cavity in which the Insect dwells. A formation of this kind on the leaves of Aegopodium podagraria is described by Thomas[[513]] who states that the growth is due to the deposition of an egg of the Psylla, and is independent of the after life of the Insect; a fungus—Puccinia aegopodii—forms similar structures on the leaves. Structures much more definite than this may be the result of the attacks of Psyllidae; for an example the reader may refer to Réaumur's account of Psylla buxi.[[514]] In Australia and Tasmania there are Psyllidae known as Laap or Lerp Insects, the products of which are called leaf-manna or Lerp, and are used as food. This manna is a scale produced by the young Insect on the leaves of Eucalyptus as a covering or protection. The scale is fastened to the leaf by a hinge, and is somewhat like the shell of a cockle. Although the scales are said to be in some cases objects of great beauty, very little is known about these Australian Psyllidae, one of which has, however, been referred by Schwarz to the genus Spondyliaspis, Signoret.[[515]] About 160 species of Psyllidae are known to occur in the Palaearctic region, and about fifty of them have been found in Britain.[[516]]