Wings rudimentary, in the form of scales, situated on the mesothorax and metathorax. Mouth suctorial. Metamorphosis complete.

This order comprises the Fleas (Pulicidae), which are parasitic upon different animals. The larva of the common Flea (Pulex irritans, fig. 187) is an apodal grub, which in about twelve days spins a cocoon for itself, and becomes a quiescent pupa, from which the imago emerges in about a fortnight more.

Fig. 187.   A, The common Flea (Pulex irritans) ; B, Larva of the same ; C, Pupa of the same. All the figures are greatly magnified. (After Westwood.)

Fig. 187. - A, The common Flea (Pulex irritans) ; B, Larva of the same ; C, Pupa of the same. All the figures are greatly magnified. (After Westwood.)

The Chigoe or Sand-flea (Sarcopsylla penetrans) of the tropical parts of America, is a more serious pest than the common Flea. It is, however, only a parasite as regards the impregnated females; the males, unimpregnated females, and larvae leading a free existence. The impregnated females, however, bore their way through the skin of the foot in the human subject, and live there till they assume the size of peas, by the distension of the abdomen with eggs, often occasioning great local irritation and inflammation. They also live beneath the skin of mice and dogs.

Many authorities regard the Aphaniptera as a degraded group of the Diptera.