ENTOMOLOGICAL SOCIETY OF ONTARIO. 29 



Report, or to his Bulletin on the Horn-fiy (Central Exp. Farm, No. 14.) As the dairy 

 and stock-raising interests of Canada are of such great importance it is sincerely to be 

 hoped that *-.his plague of flies is but a temporary one. 



Parasitism in Inskctp. 



This, to me, is one of the most interesting problems in entomology, and the subject 

 has been admirably dealt with by Prof. Riley, in his address as President of the Entomo- 

 logical Society of Washington last year (Proc. Ent. Soc, Wash., Vol. II., pages 397- 

 431). After a mention of the animals affected (chiefly mammals, birds and insects), he 

 defines the scope and meaning of the term pirasite, and suggests the separation of para- 

 sitic forms into three groups. First, Parasites Proper, including insects whose whole life 

 is passed upon and is dependent upon their host, and which may be sub-divided into ex- 

 ternal, as lice, and internal (or sub-cutaneous), as the itch-mite, etc. Second, Fatal 

 Parasites, which, in the larval stage, live at the expense of the member.s of their own 

 class. These are also sub-divided into t/z<ernaZ, where the larva is nourished within the 

 host upon the surrounding fluids, as are the majority of Hymenopterous parasites, and 

 external, where the larva attaches itself to the host, as in Thalessa, and sucks its juices ; 

 to this sub-division belong many hymenopterous, dipterous and coleopterous parasites. 

 Third, InqnUinous Parasites, which includes the numerous forms which live upon the 

 provision made by other species for the sustenance of their offspring, or which are found 

 habitually associated with other insects, but not injurious to them. This class is sub- 

 divided into fatal inquilines, where the guest's living means starvation and death to the 

 host, and commensals, where association is mutually harmless, as where beetles are found 

 living in the nests of bees and ants. 



An outline is then given of theparasitic forms occurring in the several orders of insects, 

 with reference to some of the principal and more interesting groups. The Hymenoptera 

 furnish by far the greatest number of species, which, by their abundance and rapidity of 

 reproduction, tend to check and reduce the undue prevalence of other insects. Some of 

 the most interesting parasites belong to the Coleoptera, especially those forms of which 

 the larva? in the first stage are named triungulins, and which later, when the host has 

 been reached and food assured, gradually become helpless grubs. Such are the Oil-beetles 

 and Blister-beetles in the larval stages. The Diptera furnish the well-known Tachinid 

 flies which deposit their eggs upon caterpillars and other insects, the footless maggot 

 penetrating the body of the victim and feasting therein. Tliese forms are very numerous 

 and destroy enormous numbers of insects, such as the Tent-caterpillars, etc. The order 

 furnishes also many other important groups of parasitic species varying much in habits, 

 such as the bot-flies and tick-flies. We may also include under this order th& fleas. In 

 the Hemiptera are found the true lice, unpleasant little creatures, subsisting on the blood 

 of mammals and not even exempting man, especially if he be indiff"r;rent as to cleinliness 

 of body and raiment. The bed-bug is often spoken of as a parasite, but is so, to such a 

 limited extent, as not to fall into any of the classes enumerated, being merely predaceous 

 in habit, a distinction which should be born in mind, as there are many predaceous insects 

 which do not come under the stigma of parasitism. 



The Platyptera (bird-lice) and Arachnoidea (Ticks and Mites) contain numerous 

 species, principally external irritants, but the remaining orders of insects are almost free 

 from any parasitic inclinations. 



The causes which might produce the parasitic habit are then considered, and the 

 effects of the parasitic life, which produces degradation both by limiting the freedom of 

 motion and by obliterating structural features common to closely allied non-parasitic forms, 

 although at the same time certain organs may gradually become highly modified and 

 specialized to meet the requirements of the new conditions of life. The modifications 

 observed are both external and internal, and form in themselves an extensive subject 

 for consideration. Finally the economic bearing of parasitism is briefly referred to, and 

 it is shown that the agriculturist is very greatly aided by the numerous species which 

 sub.'-ist upon phytophagous insects. The address is one well worthy of careful study, and, 

 as has been elsewhere remarked, would serve as a basis of a very acceptable volume. 



