KO. 15 ARTHROPOD HOSTS OF HELMINTHS — HALL 45 



sexalatus, a spirurid parasite not uncommon in the stomachs of swine 

 and peccaries, will develop to an infective third-stage larva in its 

 beetle host, and when these beetles are fed to some unusual host, such 

 as rodents, birds, or even cold-blooded animals, the larval worm will 

 re-encyst as a third-stage larva in the unusual host; but if the infected 

 unusual host is fed to a suitable primary host, the larva will continue 

 its development to maturity. How extensive this device is we do not 

 know, but it may prove to be a common means of transmitting the 

 spirurid worms of rapacious birds, as Cram has suggested, the spiru- 

 rids of these birds producing eggs which infect some arthropod host, 

 such as a beetle, the beetle being eaten by a small mammal, bird, 

 amphibian or reptile, which is infected in turn with the third-stage 

 larva, and tlje bird of prey eating these animals and becoming infested 

 with the adult worms. The investigation of these life histories is a 

 thing on which the mammalogist, the ornithologist, the herpetologist, 

 the entomologist and the parasitologist might collaborate to great' 

 advantage, and the results might show some very interesting and 

 surprising biological interrelationships. 



As intermediate hosts of spirurids, the Orthoptera are also of some 

 importance. The arthropods in question are all cockroaches, and they 

 are probably of special importance as intermediate hosts for parasites 

 of such rodents as rats and mice. These rodents seem to eat 

 cockroaches with dependal^le certainty, and the association of rats, 

 mice and roaches in the household provides a suitable and, so to speak, 

 natural combination of factors for the benefit of these spirurids. On 

 the other hand, the development of spirurid parasites of sheep, cattle 

 and horses in cockroaches inust be regarded as a case in which the 

 roach merely serves as a host for a worm which cannot depend on 

 such a host for its transmission, but which is capable of developing 

 in that host as a case of accidental parasitism. In this connection it 

 may be noted that roaches will serve as intermediate hosts for so many 

 worms in this way that these insects make excellent experiment ani- 

 mals for carrying out life-history experiments in the laboratory. The 

 plentiful supply of these insects in winter, a thing so unfortunate 

 from some points of view, is a fortunate thing for the parasitologist 

 who obtains interesting worms in winter at a time when other insects 

 are scarce, and wishes to carry out feeding experiments on some 

 insect. 



The Diptera appear as intermediate hosts of spirurids with 14 

 species serving as hosts for 3 known species of spirurids, all species 

 of the genus Hahroneina and all parasitic in horses and other mem- 

 bers of the Equidae. This association obviously depends in part on the 

 importance of the manure of horses and other Equidae as a breeding 



