VIII. INSECT PARASITES. INSECTA (part of).--The insects, properly so called (that is to say, arthropodous, evertebrated creatures, with six legs), are many of them essentially parasitic in their habits. The most important of these are “bots” and other larvæ or maggots of various flies (Diptera). The varieties of lice are also included in this group. Some few of the insect parasites are strictly entozoal in habit, at least for a part of their lifetime, being previously attached externally for a short period only. Most of the forms are essentially ectozoal. A very large number of insect tormentors, although deriving nourishment from their victims, attach themselves to the animals for so short a time that they cannot be classed as parasites under the ordinary acceptation of the term. As examples of the so-called free parasitism, the autumnal flies (_Tabanidæ_) and _Stomoxys_ may be cited. Although embracing but few strictly parasitic forms we have the following:--_Œstridæ_, _Hippoboscidæ_ (with _Melophagus_), and _Nycteribiidæ_. In regard to the maggots of _Muscidæ_ and _Sarcophagæ_, some of them are parasitic on animals and man, whilst others are parasitic upon insects themselves. The larvæ of _Conopidæ_ attack humble-bees internally. Those parasitic insects, properly so called, which, like certain of the crustaceans, are sometimes spoken of as epizoa, comprise three well-marked families. Thus, we have Pediculidæ (the source of lousiness), _Philopteridæ_, and _Liotheidæ_. Both of the latter embrace numerous species which for the most part content themselves with devouring the feathers of birds and the hairs of quadrupeds. In addition to these it may be added that some of the rat-tailed larvæ or Helophilus maggots (_Syrphidæ_) are parasitic in man and quadrupeds, as are also the larvæ of the churchyard beetle (_Blaptidæ_). The closely allied _Tenebrionidæ_ and other coleopterous families also supply various maggots possessed of parasitic habits. Fleas and bugs come under Van Beneden’s category of free parasites. This is equivalent to calling them non-parasitic parasites, an expression which looks very like a contradiction of terms.