ECOLOGY 141 



reported as sucking blood from snakes, tortoises, frogs and even 

 fish, especially when young. The very young may even swallow 

 small worms. It is thus very difficult to draw a sharp distinction 

 between parasites and predators among the leeches. Not only do 

 their habits vary during the life history of an individual, but their 

 effect on the host may vary according to its size. Thus the 

 Glossiphoniidae which have a proboscis and are equipped for 

 sucking blood may suck the entire body fluids from a small snail 

 and even finish the job by sucking up all the soft parts of the 

 animal. This is clearly predation, but young specimens of the 

 same species may live for long periods inside the mantle cavity of a 

 large snail taking only occasional meals of blood, a mode of life 

 which may reasonably be called parasitism. 



Compared with the blood-sucking leeches the macrophagous 

 forms take an even wider variety of food. Most of them will take 

 any kind of proteinaceous material that is offered, including 

 carrion or young of their own species. In fact Jung (1955) con- 

 cluded that the only consideration is particle size. In practice the 

 habits of the leech determine the food available to it, so that 

 Trocheta suhviridis which burrows in moist soil will most often 

 encounter earthworms and slugs, while Nephelopsis which remains 

 in water is particularly attracted to the corpses of fish and frogs. 

 Similarly the American species Macrohdella decora will attack fish 

 or swallow the eggs of frogs or salamanders in spite of its clear 

 adaptations to piercing the skin of mammals (Cargo, 1960). When 

 comparing the distribution of sanguivorous and carnivorous 

 leeches we find that while the former have patterns of distribution 

 related to those of their normal host organisms, the latter, which 

 are more catholic in their tastes, have distribution patterns which 

 are more closely related to physical and chemical features of the 

 environment. 



Feeding relationships are not the only ones which we should 

 consider when dealing with the relations between leeches and the 

 animate environment. Leeches also act as hosts to other parasitic 

 forms and as vectors in the life cycles of parasites of other animals. 

 In common with most other invertebrates leeches have their quota 

 of endoparasitic Protozoa. Of these, some, such as Entamoeba 

 aulastomi from the gut of Haemopis or Orcheohius herpohdellae 

 from the testes of Erpohdella are specific to the leeches but others 



