It has been stated by some writers that the mouth is truly of the sucking kind, and that the Mallophaga feed on the blood of their hosts. This is, however, erroneous; they eat the delicate portions of the feathers of birds, and of mammals perhaps the young hair. Their fertility is but small, and it is believed that {349}in a state of nature they are very rarely an annoyance to their hosts. The majority of the known species live on birds; the forms that frequent mammals are less varied and have been less studied; most of them have only one claw to the feet (Fig. 220), while the greater portion of the avicolous species have two claws. [Illustration: FIG. 219.—_Lipeurus ternatus_, male; inhabits _Sarcorhamphus papa_. (After Giebel.)] [Illustration: FIG. 220.—_Trichodectes latus_, male; inhabits the dog, _Canis familiaris_.] Most of the forms have the anterior legs small, and they are usually drawn towards the mouth, owing, it is believed, to their being used after the manner of hands to bring the food to the mouth; hence in some of our figures (219, 220) the body looks as if it had only four legs. Very diverse statements have been made as to whether allied forms of Mallophaga are found only on allied birds. It would appear that this is the case only to a limited extent, as certain species are found on quite a variety of birds; moreover, some birds harbour several species of bird-lice, even five genera having been found, it is said, on one species of bird. _Docophorus icterodes_ has been recorded as occurring on many kinds of ducks and geese; the swan, however, harbours a distinct species, _Docophorus cygni_, and this is said to have also been found on the bean-goose. At least five species, belonging to three distinct genera, have been found on the common fowl. The parasite most frequently met with on this valuable creature is _Menopon pallidum_ (Fig. {350}221), which is said to have been figured by Redi two hundred years ago under the name of _Pulex capi_. This species multiplies to a considerable extent; it is of very active habits, and passes readily from one bird to another, so that it is found on other species besides the domestic fowl. It is even said that horses kept near hen-roosts have been seriously troubled by _Menopon pallidum_, but it is suggested by Osborn that these attacks may perhaps have been really due to itch-mites. There is, however, no doubt that this species may infest poultry, especially if sickly, to an enormous extent. The dust-baths in which poultry are so fond of indulging are considered to be of great use in keeping down the numbers of this Insect. [Illustration: FIG. 221.—_Menopon pallidum_; inhabits the common fowl, _Gallus domesticus_. (After Piaget.)]