NO. 15 ARTHROPOD HOSTS OF HELMINTHS HALL 20 



larvae of worms which will develop to maturity on reaching a suitable 

 host, although larval nematodes specified as such with no further 

 discussion may be the larvae of such worms as the mermithids which 

 will develop to maturity as free-living forms. In this paper the 

 mermithids and gordians are not considered, as they are not regarded 

 as true parasites of vertebrates in the scope of treatment of that sub- 

 ject as limited here. The gordians may parasitize immature frogs in 

 the course of development of the worms, but this topic is disregarded 

 here owing to a lack of space for its consideration. 



All records which are merely surmises to the effect that a certain 

 arthropod is the intermediate host of some nematode are likewise 

 disregarded. Such surmises have their value in directing exploratory 

 research, but for the purpose of analyzing existing records to obtain 

 valid data they are worthless. There is sufficient uncertainty in con- 

 nection with a number of existing records to introduce certain ele- 

 ments of possible error as it is. 



The following list covers the important cases of arthropod hosts 

 for nematodes. The worms involved fall in the Filariata or Filarida 

 and most of them fall in the superf amihes Spiruroidea and Filarioidea, 

 two closely related superfamilies which are markedly heteroxenous 

 and hence in sharp contrast with most of the other nematode groups 

 which are usually monoxenous. In the exceptional cases in which 

 members of other superfamilies utilize intermediate hosts, the hosts 

 are never arthropods so far as the writer is aware, but are such forms 

 as fish or earthworms. 



SPIRURIDAE 



As intermediate hosts of nematodes of the Spiruridae, which is 

 made up predominantly of mammalian parasites and to a lesser 

 extent of bird parasites, the Coleoptera are of outstanding importance. 

 In this family the common mode of transmission of the larval worm 

 to the primary host is by means of the ingestion of the secondary host, 

 either as a deliberate act of eating or because of the more or less 

 accidental presence of the secondary host in the food of the pri- 

 mary host. In general, dogs, sheep, cattle and horses cannot be called 

 insectivorous animals, but the presence of beetles in their customary 

 food seems to be sufficiently common to enable various spirurid 

 parasites of these animals to maintain themselves with the aid of 

 these beetle hosts. It is evident that some of the spirurids utilizing 

 beetle hosts may have alternative life histories which are more compli- 

 cated than the mere infection of the beetle host by means of infective 

 worm eggs and the infection of the primary host as a result of swal- 

 lowing infected beetles. Thus Seurat has shown that Physocephalus 



