We investigated the response of gordian worms to predation on their host. Second, predation may affect parasite life history if the predator becomes incorporated into the life cycle 8, 9, 10. Increased virulence may also take the form of manipulating the host's behaviour 5, for example to remove it from sources of predation 6, 7. First, increased predation may select for increased parasite virulence 2, 3: for example, parasite development can speed up to minimize the period of host occupancy 4. Predation upon a host may shape parasite life history in two important ways.

Death of the worm would be expected to result from generalist predation upon the host at this stage unless the parasite were capable of an antipredator response.įew parasites have their own predators, although they are victims of those of their hosts. During this time, the cricket is active at the surface and attractive to aquatic predators such as fish and frogs (F.T., unpublished observations).

Emergence from the host occurs only after the cricket enters the water (for movie, see supplementary information) and may take as long as 10 min owing to the large size of the worm 1.

Adult gordian worms are free-living in water, where they mate as a knotted mass of multiple individuals. The induced suicide of crickets infected by gordian worms is one of the best known examples of parasite manipulation of host behaviour 1.

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