Variations in the rate of predation of the waterbugs Sphaerodema annulatum
and S. rusticum on the snails Lymnaea (Radix) luteola have been noted in respect to the morphs of
the waterbugs, size of the prey individuals, densities of prey
and predators, temperature and surface area of the waterbody
concerned and the seasons. Consumption rate was highest (7.2
and 2.2 individuals per day per individual of S. annulatum and
S. rusticum, respectively) in pre-reproductive ages of the
waterbugs. This was followed by a gradual decline with the
increase in age of the predators. The consumption rate was
gradually higher with the increase of temperature from 20 C to
35 C The bugs failed to survive beyond 35 days at 35 C Though
the bugs prey upon the snails of all sizes preference for 6.5
x 4.5 mm to 8 x 5 mm individuals by S. annulatum and for 5 x 3
mm to 6.5 x 4.5 mm individuals by S. rusticum is established.
The waterbugs, irrespective of species, consumed the snail
individuals belonged to 3 x 2 - 4 x 3 mm size group maximum
when supplied separately. The rate of predation gradually
declined with the rise of predators density irrespective of
Predation rate increased with increasing prey density.
This was level off when the prey snails were 1100 and 700 in
number for S. annulatum and S. rusticum respectively. An adult
S. annulatum and S. rusticum consumed 5.04, 3.7, 1.43 and
3.36, 2.49, 1.04 snails per day respectively in summer,
monsoon and winter.