Peering at pond predators

As our garden pond develops, so does the community of invertebrates that live within it - and this of course means predation. Predators come in all shapes and sizes, from tiny water mites to herons. One vertebrate predator is a neighbour's cat (which does not like being sprayed with water!); another is the smooth newt Lissotriton vulgaris. Our pond currently has a pair of these, so we will be looking out for eggs - they are also voracious predators of frog tadpoles (of which there are many) and one was seen yesterday taking a tadpole as prey.

Female smooth newt Lissotriton vulgaris

Other predators are smaller (in the absence of fish which are likely to devour/reduce the biodiversity of a garden pond) in the form of various invertebrates. Some of these are familiar and commonly seen, such as the pond-skater Gerris lacustris (there are other species, but this one is often an early coloniser of newly created ponds). Being a true bug (Hemiptera), it has piercing mouthparts (which curve back under the head) and can be seen skating on the surface held up by surface tension. Pond skaters can move quickly when disturbed or darting towards prey such as smaller invertebrates that have fallen onto the water's surface. Their feet and legs dimple the surface and the large middle pair of legs push backwards, creating a pressure wave that allows the insect to glide forwards (e.g. Guthrie 1989).

Pond skater Gerris lacustris. The dimples in the water's surface are clearly visible - also note that this specimen is fully winged; spring dispersal flights are an important part of this species' life history.

Lastly, a quick look at a group well known as predators in their juvenile form - the Odonata - dragonflies and damselflies. There are several small early-instar nymphs of the Large Red Damselfly Pyrrhosoma nymphula in our pond, but also a late/final-instar nymph as shown below. Although often lurking in sediment (this one was underneath an aquatic plant pot/basket), they can swim actively, have excellent vision and of course hinged mouthparts (the 'mask') which can be quickly thrust forwards to grab prey. Nymphs of the Odonata will attack many types of prey - not only other invertebrates, but also amphibians, especially small/juvenile individuals. It is likely that our large population of frog tadpoles may start to be reduced soon...

Late-instar nymph of the Large Red Damselfly Pyrrhosoma nymphula. The partly darkened caudal lamellae at the tip of the abdomen can be seen, plus the bulges and central indent at the back of the head - these features are useful for identification.

Late-instar nymph of the Large Red Damselfly Pyrrhosoma nymphula. The large eyes, useful for locating prey, are shown - the jawed 'mask' is retracted beneath the front of the head.

Reference

Guthrie, M. (1989). Animals of the Surface Film. Richmond, Slough.