Bubble-butts and water-walkers

It's about a month since we lined and filled our garden pond and it took less than 24 hours for the first invertebrates to find and colonise it (they were small Hydrellia flies which formed a breeding swarm within 48 hours). Since then, things have moved on - as covered in a recent post, dragonflies and damselflies have already found it, the large water mint (Mentha aquatica) is proving very popular with nectar-feeders, and a common frog (Rana temporaria) has taken up residence at one end.However, I want to look at a couple of other pond residents - beetles and bugs (that's the Hemiptera or 'true bugs' rather than bugs in the general sense...).

A water beetle Rhantus suturalis on bare new pond-liner - its breathing air-bubble is visible at its rear.

The largest beetle currently present is Rhantus suturalis (photo above) which as about 12mm long excluding appendages - note the 'smudged' dark mark on the centre of the pronotum. This is probably the most widespread water beetle worldwide, being found from northern Britain to New Zealand (Foster & Friday 2011). It tends to be associated with stagnant water in lowland areas, often in newly created or polluted situations - our pond is neither stagnant nor polluted but is certainly new and this beetle appeared within about a week, possibly transferred with water plants. This specimen seems to spend much of its time hiding under the bridge over our pond, but is also seen regularly swimming rapidly around the pond, including visits to the surface where it exposed its rear to replenish the air bubble used for breathing.There are some other small dark water beetles which I have yet to capture and identify (I'm tempted not to disturb the pond much at this early stage), but also beetle larvae.

Beetle larva in side view

Beetle larva in dorsal view

Again, I haven't identified this larva (yet) though it does look like Rhantus, maybe a smallish early stage - time will tell, but there are several which can be seen swimming actively to and from the surface. Meanwhile, up on the surface, taking advantage of surface tension to allow propulsion, pondskaters of the genus Gerris, probably the common pondskater G. lacustris, hunt for prey items that fall into (or rather, onto) the water. This species is well known as an early coloniser of new ponds (Denton 2007) and can be seen skating rapidly towards potential prey which is then pierced with the tubular mouthparts.

A pondskater Gerris lacustris, an early coloniser of new ponds

As well as predation, I have witnessed both reproduction (copulation) and aggression between Gerris. The latter appears to be as a result of encounters between males (some are territorial, actively courting approaching females) which are brief, in the form of immediate attack and retreat. Females also hold territories based on food supply. The sexes signal to each other by making ripples with the legs and abdomen, the frequency indication whether the sender is male or female. Males then judge which it is and act accordingly with 'courtship' or 'repel' signals, though they are not always correct (Savage 1989)!

So, although the pond is unlikely to mature that much more before next spring when the first full plant-growing season starts, an aquatic community is beginning to develop and will undoubtedly feature here from time to time as interesting species and behaviour catch my eye.

'Til then, if you'd like more info about creating a wildlife-friendly garden pond, why not download an advice booklet here (from the excellent Pond Conservation).

References

Denton, J. (2007). Water Bugs and Water Beetles of Surrey. Surrey Wildlife Trust, Woking.
Foster, G.N. & Friday, L.E. (2012). Keys to the adults of water beetles of Britain and Ireland (Part 1) (2nd ed.). Handbooks for the Identification of British Insects 4(5): i-iv, 1-144.
Savage, A.A. (1989). Adults of the British Aquatic Hemiptera Heteroptera. A Key with Ecological Notes. FBA, Ambleside.