H. ephippiger nymphs are able to devour and consume
substantial numbers of the medically important snail
L. natalensis although the rate of consumption varies with snail
size and prey density. The consumption rate increased with
increasing the prey density. Odonata predators are cited as
important bio-control agents against mosquito larvae in lakes
and ponds [19,20]; although their use in snail regulation in these
habitats has not been recorded. The nymph encountered and
attacked small, medium and large L. natalensis snails. Most
aquatic insects detect their preys by mechanical, vibratory or
visual cues and react to the slightest agitation of the water [21].
The Odonata nymphs are sprawlers and snatch the moving
prey in ambush, rarely hunting for the prey [22]. Starved
predators required shorter time in attacking (searching) and
handling time towards the preys in comparison with the
satiated predators. Searching and handling times are major
factors in the determination of the functional response of the
predator to its prey and should predict how the predators
behave when different prey species were presented [23]. The
predation rate of H. ephippiger on the freshwater snails was
found to vary with snail size and density of the prey. The
predation rate varied significantly against snail sizes at
different density. A low predation rate was observed against
large snails, likely due to the greater amount of time required
to prey those snails. In natural situations where the habitat is
structured and the temporal and spatial variations of species
abundance is more complex, the predation rates of the
Odonata nymph are expected to vary as has been noted in
other aquatic predators [24]. The present study suggests that
the Odonata H. ephippiger nymph is a potential candidate as a
bio-control agent sharing the same habitats of snails. Thus the
use of the Odonata nymph alone or in combination with other
aquatic insects can be viable option for regulation of freshwater
snails in wet lands as an extension of conservation biological
control. This proposition needs to be tested under field conditions
to promote regulation of these snails and conservation of
useful insects.