I CANNOT RESIST telling one fluke story which borders on the dizzy horrors of science fiction. [A fluke is a wormlike parasite that is evolved from the flatworm and a brother to the tapeworm.] This concerns the sheep-liver fluke, Fasciola hepatica. Until 1963 it was generally accepted that this animal used only the mud snails as intermediate host. However, it was discovered that the fluke as a cercarian [larval or immature] form does not willingly leave the snail's body. It is ejected.

The snails embed the cercariae in balls of mucus and expels them. These balls of mucus are devoured by another intermediate host, the ant. In this insect they encapsulate in the abdominal cavity and mature to the form that is so dangerous to the sheep's liver. The question is, how do they get from an ant's stomach to a sheep's liver?

Clustered together, the infected ants hang for hours, offering themselves to be eaten by sheep or cattle, who of course oblige.

By a very strange process indeed. A single cercaria works its way to the brain of the ant and "takes over." Henceforth the ant is an automaton of a kind it was not intended to be. Under the direction of the primitive creature dominating its nerve center, the ant is compelled to do things it would never dream of doing. It climbs to the very tips of grasses and weeds and waits there. Clustered together, the infected ants hang for hours, offering themselves to be eaten by sheep or cattle, who of course oblige. The rest is routine for the fluke.

One needs to know more about the process of how a single larval trematode [fluke] is able thus to physically hypnotize an insect as sophisticated or as occupied with its own deep instincts as an ant, since it introduces a new dimension in entomology as well as parasitology. It offers perhaps the ultimate in puzzles as to the workings of instinctive behavior.

[A lesson for those of you who need yet another reason not to eat someone's boogers... ;>)]