SCIENCE-GOSSIP. 



in 



HAIR-WORMS AND THEIR HOSTS. 



By Harry Moore. 



A T Betch worth, Surrey, just where the road 

 T* crosses the River Mole, I picked up a speci- 

 men of Pterotichus madidus, Fab., from which, 

 upon being placed in the cyanide bottle, a Gordius 

 aquaticus, L., endeavoured to escape. About three 

 inches of it extrude, and, judging by its girth, an 

 equal or greater length remains inside, yet the 

 abdomen of the beetle is but nine millimeters 

 in length. 



Nearly every observer of the slightest experience 

 has some acquaintance with hair-worms, even if it 

 is only a hazy recollection of the horse-hair legend 

 of his school days. Numerous notes are scattered 

 through the early volumes of Science-Gossip and 

 a further one upon the variety of the hosts Gordius 

 infests may not be unacceptable. The family 

 Nematoidas to which the Gordiacece belong, contains 

 many species of more than ordinary interest, first 

 on account of their curious cycle of development, 

 and then their value in the economy of nature, 

 for not only are they in a measure beneficial in 

 checking over production in certain insects, but 

 more or less dangerous when introduced into the 

 human system. Their life history may be briefly 

 described as follows : the eggs are laid in long 

 strings ; upon hatching, the young larva bores 

 through the membrane, and for a short period lives 

 a free aquatic life. It then becomes parasitic upon 

 various fly larvae, etc. ; these hosts in their turn are 

 devoured by other creatures, and the worms become 

 incepted in their intestines, where they remain 

 some months, finally making their way into the 

 intestinal cavity and escaping per ano in due course. 



It is rather singular, however, that, whereas 

 hair-worms are most commonly found infesting 

 beetles in England, they prefer the orthoptera 

 (grasshoppers and allied insects) in America. In 

 both countries spiders have been noted as hosts, 

 in America the human being, and an instance has 

 come under my own notice, where there was strong 

 presumptive evidence the worm had been voided 

 by a sparrow. Various writers cite fishes and 

 frogs, and several mention caterpillars, but the 

 parasites observed in lepidopterous larvae probably 

 belonged to the allied genus Mcrmis. In America, 

 Mermis acuminata, Leidy, has been observed in the 

 larvae of the codlin-moth (Carpocapsa pomonella, L.) 

 and a similar parasite has been seen in larvae by 

 several of our London workers. 



In enumerating the hosts of Gordius aquaticus, 

 the common European hair-worm, several diffi- 

 culties arise, for whereas, as I have already 

 mentioned, carnivorous beetles are chiefly infested 

 this side of the Atlantic, the observers do not 

 always seem to have determined their species. 



Several references of this sort will be found in 

 Science-Gossip (vol. i., page 198, vol. xii., page 

 71, vol. xv., page 281, etc.). If any of our present 

 readers can furnish something more definite, we 

 shall be able to get along with our list. I have 

 come across no mention of coleoptera being 

 infested in America, in any note to which I have 

 access ; but the following are some of the authen- 

 ticated instances among the orthoptera. G. 

 aquaticus has been found in the cricket (Gryllus 

 neglectus), and in Acheta abbreviatus, Serville — the 

 short-winged field-cricket found in woods beneath 

 logs and stones ; Gordius robustus, Leidy, infests 

 Stenopelmata fasciata, Thomas, one of the stone or 

 camel crickets usually found beneath stones and 

 along the margins of woodland streams and logs, 

 and in damp woods (Blatchley), and Orchelimum 

 gracile, a grasshopper confined to low moist 

 meadows; A. Gordius (species ?), eight and a half 

 inches long, has been taken from a pupa oiXiphidium 

 ensiferum, Scudder, whose perfect body measures 

 but half an inch in length. The life history of 

 this orthopteron is of exceptional interest, the ova 

 being deposited from several up to one hundred 

 and seventy " in the turnip-shaped galls, produced 

 by a small fly belonging to the Cecidomyidae on 

 certain species of willow (Salix cordata, etc.)." 



I have now but to mention Caloptenus spretus, 

 Thomas, the Rocky Mountain locust, which is 

 infested with G. aquaticus, Linn., and G. varius, 

 Leidy, although repeated dissections by various 

 American observers (Riley, Whitman, etc.), have 

 shown that not more than a small percentage of the 

 locusts are infested, yet when we consider the loss 

 incurred annually in the United States from locusts 

 alone is estimated at ^8,000,000, anything which 

 tends to mitigate the plague becomes of importance. 



The question — how are we to account for the 

 presence of these aquatic parasites inside terrestrial 

 insects ? — upon consideration, is not of easy solution. 

 Of course they are introduced with their food while 

 in a minute immature state, but whether as ova or 

 larvae I think there is room for discussion. It will 

 be noticed all the insects mentioned are associated 

 with damp places that are more or less subjected 

 to floods ; but I do not think that sufficient reason 

 for believing they have all fed upon the various 

 aquatic fly larvae in which the hair-worm larvae are 

 said to pass their first period of larval life, though 

 in the case of grasshoppers, Packard thinks they 

 swallow them as larvae. I am inclined to believe 

 there are several points in the life history of these 

 parasites yet to be cleared up ; perhaps some of 

 our microscopists can elucidate them. 



12, Lower Road, Rotherhithe, S.E. ; Sept., 1895. 



