HOMES AND GARDENS - POND LIFE




 

 

Ponds are popular with homeowners and providing there are few or no ornamental fish they provide a splendid resource. Water is essential for mammals and birds to drink, and for birds as somewhere to bathe and keep their plumage in top order as well. For amphibians, some reptiles and invertebrates they are ideal or vital for breeding.

Common Toads (Bufo bufo, 10cm) spawn in March, later than Common Frogs, and are commonplace as well as welcome in gardens. Quite why the term toad is used pejoratively in common parlance is a mystery given how harmless and helpful they are, notably at getting rid of slugs in a border or vegetable patch. Since they spend most of their lives out of the water, a small pile of stones, bricks or logs out of the sun can provide a good base for them.

Grass Snakes (Natrix natrix, to 150cm) eat toads but are much less common in gardens than the prey. Compost heaps or piles of leaves can provide the right micro-climate for breeding. Even though not poisonous, the species sometimes gets dealt with summarily and unjustifiably, suffering from the standard human syndrome about serpents.

Any pond without netting on top and containing fish or amphibians is likely to attract Grey Herons (Ardea cinerea) but since fish are rarely good news for native invertebrates in such locations a genuine naturalist is unlikely to be bothered by a heron turning up now and then. It is a treat to be able to study them at close quarters, and providing the pond has deeper areas the amphibian population is safe enough on a long-term basis.

Dragonflies and damselflies are quick to colonise a new pond, with the Southern Hawker (Aeshna cyanea, length 70mm), Common Darter (Sympetrum striolatum, length 55mm) and Large Red damselfly (Pyrrhosoma nymphula, length 35mm) among the first to arrive. Broad-bodied Chasers (Libellula depressa, length 60mm) are often not far behind and are relatively easy to watch since they are great perchers in the sun.

There always needs to be sufficient prey to keep the hungry dragonfly and damselfly nymphs satisfied for up to two years – further north, the larval period tends to be longer. For the larger species, prey includes almost anything that moves in the water.

There can be large numbers of Southern Hawkers emerging over a period of a week or more – they are not synchronised in this – and unlike many species they emerge at almost any time of day. The whole process of crawling out of the water, leaving the exuviae (larval case), pumping fluid into the wings then flying away takes at least an hour. Oddly, Southern Hawkers can try and oviposit in a wide variety of substances, some of them hopeless such as rocks and shoes.

As with the Common Darter, which has a red male and yellow female, the Broad-bodied Chaser male and female vary in colour, with the male a striking blue on the upper side of the abdomen and the female yellow-brown. Large Red damselflies are the same colour for both sexes, are very common and are early to emerge, seen from April to September. Like all other Odonata, they need to go somewhere safe to dry out and strengthen after emerging; most go into woodland but Large Reds can turn up on walls or, once that I saw, on a food cover at a picnic table.

Carnivorous species on or close to the surface film include Backswimmers (Notonecta glauca, 15mm) and Pond Skaters (Gerris lacustris, 10mm). The former, which can prey on fish fry using their strong forelegs and vigorous bite, retain air in the hairs on the stomach and under the fore-wings (elytra) but need to replenish the supply regularly by poking the abdomen above the water level.

Pond Skater nymphs live in the water and the adults hibernate under cover away from the pond. They are fierce predators with a powerful proboscis, capable of killing any invertebrate that falls in the water including social wasps. The legs are effective at detecting potential prey, and for running fast across the surface film. Pond Skaters sometimes feed communally on large prey though disputes can break out.

Water Measurers (Hydrometra stagnorum, 11mm) are slim but tough predators who cannot fly. They spend their time lurking among plants in or around the margins of ponds, lakes and rivers awaiting suitable prey. When such morsels appear, they are swiftly hunted down and pierced by the sharp beak. A more colourful but similarly common insect found on the surface of ponds of all sizes is the Semaphore Fly (Poecilobothrus nobilitatus, 7mm), a so-called long-legged fly from a family associated with wet areas, the Dolichopodidae. The adults are typically found wherever there is pond-weed or algae. Larvae are believed to be predatory, developing in damp soil, and adults certainly are, feeding on a range of invertebrates. The male has white tips to the wings.

Images © Jeremy Early. All rights reserved.

In 2013 I published My Side of the Fence – the Natural History of a Surrey Garden. Details may be found, and orders placed, via this hyperlink My Side of the Fence. In November 2015 Surrey Wildlife Trust published the atlas Soldierflies, their allies and Conopidae of Surrey, jointly written by David Baldock and me. Details are on this web page: Atlas.

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