Mermis Parasitic on Ants of the Genus Lasius. 355 



flight by throwing some of them into the air, but in no case were 

 they able tc fly at all. 



It was not until 1916 that I again met with mermithogynes, this 

 time in Somerset, in the marshes by the sea at Porlock, where examples 

 of both L. jiavits and L. alienus were abundant early in July 

 (Crawley, 1916). The proportion of parasitized to normal females 

 varied considerably according to the colony, Ijut it was only in a 

 small number of cases that the parasitized females outnumbered 

 the others. The colonies were all large and flourishing in 

 appearance. 



Again, in July 1917, I came across many more mermithogynes 

 of both the above species in the same locality, but in every case 

 the normal females greatly outnumbered the mermithogynes, the 

 a\"erage proportion not being more than 1 to 12, and in one nest 

 only a single mermithogyne was found. 



On my return home I placed these ants in " Janet " plaster 

 nests with workers, males and pupte. 



At the end of the month two of the L. fiavus mermithogynes 

 became very restless, elevating their wings and curving their 

 abdomens as if disturbed by the movement of the worms. One 

 constantly bit the end of her gaster from which the head of the 

 worm could be seen to protrude. At night one of the ants, pre- 

 sumably this one, was dead, and the worm had emerged and was 

 lying dead among the worker ants, who were biting it. This 

 seemed to indicate that in nature the worm would not emerge 

 until the female had left the parent nest on the marriage flight. 

 As stated above, the parasitized females do leave the nest at this 

 period, though unable to fly, with the normal females. Within 

 the next few days three more mermithogynes had died, without the 

 parasites having emerged, and all had shown restless symptoms 

 previously. The movements of the worms could be distinctly seen 

 through the distended walls of the gasters of the dead ants. One 

 day after the death of a female the parasite pierced the integument 

 just below the anus and began to emerge. After attempting in 

 vain to force its head under the soil, it succeeded in getting clear 

 of its host's body in just over an hour. I then placed the worm 

 on a piece of turf, but it was unable to ])ierce the turf, and 

 eventually died. 



By August 10 all the mermithogynes, except one L. Jiavas, 

 were dead, but in only one case had the parasite completely 

 emerged, and in one or two others it had partially done so. Some- 

 times the worm pushed its head through the anus itself, in other 

 eases it was between two of the ventral plates of the gaster tliat 

 the aperture was made by the parasite. It should be noted in 

 passing that the thoraces of all the mermithogynes I examined 

 were almost completely empty, and did not contain the large 

 wing-muscles of tlie normal female which are later on used as 



