WORMS l8l 



about the length of a pin which Uves fixed in the trachea of the host and 

 is the cause of the disease known as the gapes. Chickens can become 

 infected in two ways. Either they ingest embryonated eggs which have 

 passed out with the bird's droppings and have developed while lying on 

 moist ground; or they can eat earthworms into which the recently 

 hatched larva has penetrated and subsequently encysted. Various 

 authors claim that birds are easier to infect in the laboratory if they are 

 fed with earthworms containing cysts, rather than the embryonated 

 eggs. House flies, green-botde flies, springtails and centipedes also act 

 as transport hosts. When infected they become sluggish and are easily 

 caught. Certainly in nature birds can become infected by both the 

 direct and indirect method. After the gapeworm has been swallowed 

 by the avian host it escapes from the intestine and migrates — possibly 

 via the blood stream — to the lungs. Some time is spent in this site before 

 the worm moves on and takes up its final position in the windpipe. 

 Sygnamus copulates while still immature and the male and female remain 

 joined together for hfe, thus forming a characteristic Y-shaped figure 

 (Plate XXVIIb). Only a portion of ingested embryonated eggs reaches 

 maturity. From 10,000 larvae fed to a turkey only 235 pairs were 

 recovered from the windpipe and lungs — but this was sufficient to kill 

 the host. The gapeworm is a cosmopolitan species of which there may be a 

 number of different wild strains. The most highly infected hosts in 

 Britain are rooks and starlings but there have also been records from 

 the robin, little owl, magpie, jay, carrion-crow, jackdaw, kestrel, house- 

 sparrow, purple sandpiper and several others. Young birds are much 

 more susceptible than adults and often a very high proportion of nest- 

 lings harbour these worms, whereas only a small percentage of the 

 parent birds in the same population are infected. In the case of 

 partridges the females are more susceptible than males. An allied 

 species, Syngamus merulae, is found in thrushes and blackbirds in 

 Britain. 



Another well known parasite of the chicken and wild birds, which is 

 also placed in the same order, is Trichostrongylus pergracilis. This is a 

 small species less than a centimetre in length which may be found in 

 thousands in the caeca of infected birds. In Britain it has only been 

 recorded from the grouse and occasionally the partridge. The life- 

 cycle is direct. The eggs pass out with the droppings and hatch in about 

 two days. Two moults take place and at the end of a fortnight the 

 larvae become infective. When the dew is on the grass or after rain they 



