hy birds of the Common Earwig (Forficula auriculana) 169 



numbers of gregarines of different sizes or between the proportion 

 of free gregarines to those in syzygy in their low and high male 

 hosts respectively. 



During our stay on the Scilly Islands in 1912 Capt. Potts and 

 myself, in company with Capt. J. T. Saunders, found in St Martin's 

 several earwigs parasitised by a gordiid larva {sp. incert.), the coils 

 of which, though projecting between the terga of the abdomen, 

 seemed to have no effect on the health and activity of their hosts. 

 The same apparent absence of deleterious effects was noticed in 

 three of the Porthcressa batch of 1917 which were found to be 

 similarly infected. In one, a low male, a large gordiid occupied 

 most of the body, and no portion of the alimentary canal posterior 

 to the crop could be found ; in a high male similarly infested by a 

 large gordiid there was very little of the hind gut left ; and an adult 

 female contained three or four gordiids of various sizes, the gut in 

 this case being intact and apparently healthy. A fourth individual, 

 a low male, was not parasitised when examined, but as the gut was 

 partially atrophied, it had probably been recently deserted by a 

 gordiid. All these infected individuals seemed as active and 

 healthy and to possess fat bodies as large as those not infected ; 

 the earwig's resistance to such extensive destruction of internal 

 organs is very noteworthy. As Clepsydrina ovata inhabits the 

 chylific ventricle and hind gut and as the presence of gordiids 

 evidently often results in destruction of these portions of the 

 alimentary tract, the latter parasite is likely to be exclusive of 

 gregarines, and these were absent in all three of the males 

 mentioned above (including that with the hind gut intact), while 

 only two were found in the female. 



That the presence of parasitic worms has sometimes serious 

 effects on the insect's health is suggested by the recent observations 

 of Jones recorded in " The European Earwig and its control," 

 a report on the invasion of Newport, R.I., in 1911 by Forficida 

 auricularia and its subsequent spread ( f/. >§. Dept. Agric. Bidl. 566, 

 Washington, June, 1917), from which it appears that 10 per cent, 

 of earwigs kept in the laboratory were killed by the infection of a 

 worm identified as Filaria locustae, whose average length is given 

 as 83 mm. This however is a size exceeding considerably that of 

 the gordiids in the Scilly earwigs, which I have called " large " 

 when attaining a length of 50 mm. 



In southern Russia Forficula tomis, Kolenati, is parasitised by 

 the tachinid fly, Rhacodineura antiqua (Pantel, Bull. Soc. Entom. 

 France, No. 8, Paris, 1916, p. 150), but I do not know if it attacks 

 the common earwig. The paper quoted mentions the capture of 

 the adult fly in Holland and Portugal. 



Lucas {Entom. XXXVII. 1904, p. 213) reports F. auricularia 

 (or ? lesnei) attacked by scarlet acarine mites. 



