FROGS, TOADS AND TADPOLES
The frogs and toads of the order Anura differ from the inferior batrachians principally in form. The tail is absent, and instead of long, slender bodies and small legs, or none, they have short, squat, triangular bodies and hind legs, at least, of relatively great size and strength, whereby they progress when on land by leaps instead of by running or creeping; some are almost wholly aquatic in habit, others almost wholly terrestrial or arboreal. The ossification of the bones is far more complete, the eyes and ears (represented by the large tightly drawn membrane, the "tympanum," on each side of the head, covering the internal ear) are well developed, and the voice is louder than in the urodeles, which can do little more than squeak. The mouth is usually large and cleft to beyond the eyes. The tongue, used to capture prey, is not thrust straight forward, but thrown "overhand," as it were, catching the insect aimed at in its curling and sticky tip.
All frogs and toads are flesh eaters, mainly of worms and insects and larval or small water animals; but the big species, such as the bullfrog, may seize prey of considerable size as it comes within reach, such as young ducklings. None hunt about for prey, but, aided by the concealing nature of their colors, wait quietly until a victim comes within reach of their quick and accurate tongues. All lay their eggs in still water, varying in number from a few score to several thousands, according to the species. In all cases the young are hatched in a larval form, called "tadpole," having a tail and gills, and this gradually changes into the adult, tailless form of the adult. On emerging from the egg the embryo has a very large head and body. In a frog the external gills and the long, compressed tail are only feebly developed when the tadpole is first hatched, while the mouth is provided with a much developed adhesive apparatus, by means of which the young attach themselves to plants or other objects. The tadpole changes by regular stages into the adult form, the tail being slowly absorbed into the body from which the legs grow out.
The Anura are separable into two suborders:
1. Aglossa—Having no tongue.
2. Phaneroglossa—Possessed of a tongue.
The Aglossa are few in number, and belong to southern Africa and tropical America, where the group is represented by the famous Surinam toad, whose eggs are fixed in separate pits or "pouches" in the spongy skin of the mother's back, where they are placed as fast as laid, by aid of the male.
The Phaneroglossa contains several families, the first of which, Discoglossidæ, is characterized by the round, nonprotrusible tongue, and includes species of toads belonging mainly to the Mediterranean region, two of which are familiar to most readers of natural histories.
It may be well to say at this point that the terms "toad" and "frog" do not express scientific distinctions, although generally applied by naturalists to the first three families of the list, and especially to the Bufonidæ; but mark the facts of popular observation that the members of these families are more terrestrial than the members of the families that follow them, and that they have rough warty skins in place of smooth and shiny ones; but many exceptions confuse both the classification and the use of the words—as, for example, in the case of the hylas, which you may call either "tree frogs" or "tree toads," according to your liking.
The two species mentioned above are the "unke," or firebellied toad of Germany, which when alarmed displays its scarlet underparts by a peculiar attitude calculated to surprise and frighten away an enemy. The other is the "midwife toad," most common in Spain and Portugal.
The spade-foot toads (Pelobatidæ) are a strangely distributed family inhabiting the western United States, Mexico, eastern Europe, and the Indo-Malayan region. Their special characteristic is the fact that the inner tarsal tubercle is large and is transformed into a shovel, which is covered with a hard, sharp-edged, horny sheath. Having this excellent tool these small and noisy toads rapidly excavate deep holes in the soil, preferring sand, and lie hidden during the day, but come forth at night to hunt. They resort to water only for a week or so of egg-laying in the spring, and remain unknown to most persons in whose neighborhood they are really numerous. Our common American one (Scaphiophus solitarius) is about two inches long, and brown above with darker patches.
This brings us to the typical toads, Bufonidæ, represented in all parts of the world except certain islands. A hundred pages might be filled with interesting accounts of the manners and customs of the hundred or so species, many very different from those familiar to us.
All breed in water, resorting to ponds and pools in the early spring. Where many broods have hatched the young can be met with in myriads, the ground literally swarming with them; and as they are naturally stirred up by a sudden warm rain, perhaps after a drought, people will occasionally affirm as an observed and well-ascertained fact that "it has rained toads"—something that never occurs except in the very rare cases when a cyclone has scooped the water and everything in it out of a pond and scattered it abroad.
Most of these young, migrating toads disappear as food for birds, snakes, etc., or die of disease. The food of young and old consists of insects, worms, snails, and the like; and it is an easy thing to tame toads and have much amusement in watching them at work in the early evening, for they are crepuscular in habits; and the wise gardener will see that they are not disturbed in their beneficial service of catching and devouring insect pests, unless they are so numerous as to be a nuisance.
The smallest North American toad is the oak toad of the Southern States, which is only an inch long. When, in the breeding season, these diminutive toads flock to the pools in great numbers, they keep up an ear-splitting chorus of shrill peeps, like so many young chickens.