The trapdoor spiders are those of the genera Cteniza and Atypus which dig and inhabit vertical holes in the soil, lined with silk and closed at the top by a hinged stopper or "trapdoor." Several species occur in southern Europe, one of which has a second door hanging by a silken hinge half way down the shaft; and in case of trouble the spider goes below it and pushes it above its head, so that the intruder is deceived into thinking it has opened an empty nest. Cteniza californica is the common species of our Southwest. The cover of the hole is made of dirt fastened together with threads, and is lined, like the tube, with silk, and fastened by a thick hinge of silk. The spider holds the door shut from inside. These underground homes are safe retreats for the spiders during the day, and nesting places in which their eggs are deposited and young reared; at night the spiders go forth in search of prey.
MITES AND TICKS
Mites and ticks are classified with the spiders as degenerate relatives of arachnoid stock. Ticks are large enough to be seen without a magnifying glass, and some become half an inch long. Ticks are wholly parasitic. The female lays several thousand eggs at one time on the ground or just beneath the surface. "The young 'seed ticks' that hatch from these in a few days soon crawl up on some near-by blade of grass, or on a bush or shrub, and wait quietly until some animal comes along. If the animal comes close enough they leave the grass or other support and cling to their new-found host." These parasites are the agents of the spread of several infectious diseases of cattle, the worst of which is the destructive Texas fever, and of mankind, as spotted fever and other ills resulting from the presence of blood parasites.
[CHAPTER XI]
FROM BUTTERFLIES TO BEETLES AND BEES
The generally accepted classification of the insects divides them into more than twenty orders, and these into hundreds of families whose species, already catalogued, are three times as numerous as all other known animals together. "There are, for example," as Lutz remarks, "15,000 species of insects to be found within fifty miles of New York City; more than 2,000 of these are either moths or butterflies."
Insects as a class are characterized primarily by the division of the body, when adult, into three clearly defined regions—the head, the thorax or fore body, and the abdomen or hind body. All insects have three pairs of legs, distinguishing them from the eight-legged spiders, and from the many-footed myriapods and other arthropods, and most of them have one or two pairs of wings, borne like the legs on the thorax, the abdomen never bearing either. The head consists of four segments, but in most cases the first three are consolidated into the hindmost, and are represented only by the appendages they bear. The foremost of these are the mouth organs, of which there are three pairs: the most anterior are the mandibles, next the maxillæ, and then the labium, the two latter bearing articulated prolongations known respectively as maxillar and labial palpi. The mouth has an upper lip (labrum) and contains a tongue. These mouth parts are variously modified, and by these modifications insects may be classified in two groups: "First, those in which the jaws and maxillæ are free, adapted for biting, as in the locust or grasshopper; and second, those in which the jaws and maxillæ are more or less modified to suck up or lap up liquid food, as in the butterfly, bee, and bug." It is in this latter group that we find those having those interesting relations with plants that result in cross-fertilization of flowers.
