NO. 15 ARTHROPOD HOSTS OF HELMINTHS HALL I5 



HYMENOLEPIDIDAE 



The hymcnolepicl tapeworms are predominantly parasitic in birds, 

 the above Hst of species with known life histories including 22 species 

 in birds and only 6 in mammals. An inspection of the intermediate 

 hosts for hymenolepids in mammals shows that they include members 

 of the Coleoptera, the Siphonaptera, the Mallophaga, Lepidoptera, 

 Dermaptera and the Myriapoda, of which the Coleoptera seem at 

 this time to be somewhat the more important. In the case of one 

 tapeworm, Hymenolepis diminuta, members of all the groups named, 

 with the exception of the Mallophaga, can function as intermediate 

 hosts, but such a wide range of intermediate hosts is rather unusual. 



In no case does the intermediate host appear to depend primarily 

 for its function as host on a role as food for the primary host, but 

 rather on the chance of being swallowed accidentally as a contam- 

 inating element in food, or occasionally on the fact that such primary 

 hosts as dogs will root out and swallow the fieas which are annoying 

 them. Of the 3 species of hymenolepids infesting man, all are par- 

 ticularly likely to occur in children, largely because children are less 

 careful in their food habits and in matters of personal cleanliness, 

 and are more disposed to be intimate with such tapeworm hosts as 

 dogs and cats. 



When we consider the hymenolepid tapeworms of birds, the case is 

 somewhat clearer as to the predominance of certain arthropod groups 

 as intermediate hosts and the reason for this predominance. The 

 Entomostraca, especially the Copepoda, are very decidedly the pre- 

 dominant group of intermediate hosts known at present for hymeno- 

 lepids in birds. The birds in these cases with entomostracan hosts are 

 practically all members of the Anseriformes and the role of inter- 

 mediate host in these cases is clearly also that of food for the primary 

 host. The exceptional cases, such as that of the green pigeon as a host 

 for Hymenolepis gracilis, or the chicken as a host for Fimhriaria 

 fasciolaris, must be explained as probably due to accidental swallowing 

 of an intermediate host. One can say from the available facts that the 

 intermediate host of a hymenolepid in anseriform birds should be 

 sought among the Entomostraca and that the chance of entomostra- 

 cans being the intermediate hosts is very great. The one case of a 

 malacostracan, Potamohius astacus, as a host of a hymenolepid, 

 Hymenolepis collaris. occurring in anseriform birds is regarded by 

 Railliet as doubtful, and in general the larger Crustacea are not yet 

 incriminated as intermediate hosts of avian tapeworms. 



