Order. Diptera or Siphonaptera.
Aphaniptera (Fleas).
Wingless, the thoracic rings distinct and free; antennæ of three segments; legs very powerful; abdomen with nine segments. [Ten segments are present, but only nine are visible.—F. V. T.] The mandibles transformed into serrated puncturing organs, which are situated in the split sheath of the rostrum; the maxillæ are laminated and have palpi, and more or less conceal the other parts.
The importance of fleas lies mainly in the fact that they act as plague carriers. About 150 species have already been described. The only ones of importance for this work are those found on man and those on rats and mice. The two families in which these are found are known as Pulicidæ and Sarcopsyllidæ.
The eggs of fleas are laid on the ground, on rugs, etc., and in birds’ and rodents’ nests. They hatch rapidly in warm weather and in warm climates, varying from two to five days; in cold countries they may take two or three weeks to incubate.
The larva is a footless creature, pearly white in colour, the head sometimes being darkened, composed of fourteen segments including the head, and although apodal can move with considerable agility. It lives amongst dust and dirt, and feeds upon any organic matter it can find. In about two weeks it is said to become mature, and then spins a cocoon in which pupation takes place.
The cocoons of the common human flea and the fowl flea become covered with dust and dirt. The period of pupal life seems varied, for I have had the fowl flea hatch out in ten days, and others in three weeks at the same time of year.
The adults are blood suckers and cause considerable irritation as well as acting as disease carriers, and in the Sarcopsyllidæ the females attach themselves permanently to their hosts, embedding themselves under the skin, where they become pregnant. Some kinds harbour the cystic stage of tapeworms, and the rat trypanosome passes certain stages in the rat flea. Most fleas have definite hosts, but some, like the rat and fowl fleas, attack man.
The fleas which can carry the bacillus of plague are Xenopsylla cheopis, Pulex irritans, Ceratophyllus fasciatus and Hoplopsyllus anomalus.
The two families, Pulicidæ and Sarcopsyllidæ, can be distinguished as follows: