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. 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.
Fig. 221.—Menopon pallidum; inhabits the common fowl, Gallus domesticus. (After Piaget.)
A table of the birds and mammals on which Mallophaga have been found, together with the names of the latter, has been given by Giebel.[[274]] The classification of the group, so far as the principal divisions are concerned, by no means accords with the kind of animals that serve as hosts, for the only two genera peculiar to quadrupeds (Trichodectes, Fig. 220; and Gyropus) belong to the two chief divisions of Mallophaga. The genus Menopon includes numerous species found on birds, and three or four others peculiar to mammals.
Two very natural divisions, Philopterides and Liotheides, were adopted by Giebel and Nitzsch, but unfortunately the chief character they made use of for diagnosing the two groups—the presence or absence of maxillary palpi—was illusory. Apparently the labial palps will serve the purpose of distinguishing the two divisions, they being present in the Liotheides and absent in the Philopterides. A table of the characters of the avicolous genera of these two groups is given by Grosse.[[275]]
The Liotheides are more active Insects, and leave their host after its death to seek another. But the Philopterides do not do so, and die in about three days after the death of their host. Possibly Mallophaga may be transferred from one bird to another by means of the parasitic two-winged flies that infest birds. The writer has recorded[[276]] a case in which a specimen of one of these bird-flies captured on the wing was found to have some Mallophaga attached to it.
We should perhaps point out that these Mallophaga, though called bird-lice, have nothing to do with the true lice which are so frequently found with them, and that live by sucking the blood of their hosts. It would in fact be better to drop the name of bird-lice altogether, and call the Mallophaga biting lice. Trichodectes latus, according to this method, would be known as the biting louse of the dog, the true or sucking louse of which animal is Haematopinus piliferus, and belongs to the anoplurous division of Hemiptera.
Fam. II. Embiidae.
Elongate feeble Insects; with small prothorax, elongate meso- and meta-thorax, which may either bear wing or be without them. In the former case these organs are not caducous, are delicately membranous, and all of one consistence, with three or four indefinite longitudinal nervures and a few cross-veinlets. The development is incompletely known. The individuals do not form organised societies.