Diary of a farm pond: April 2011

As you may know from one or two other posts, and the 'Wildlife of Highbridge Farm' page over on the right, about a year ago I got involved with a community farm project at Highbridge Farm, Hampshire, southern England. Although its main function is to grow cheap, chemical-free food without reliance on oil/petroleum products (it's a project of the local transition group, ETNet ), this comes with an interest in, and reponsibility for, wildlife and the wider environment. So, formed from an old farm gravel pit, a pond has been created and I intend to follow its development as a wildlife habitat.

The pond/gravel pit, summer 2010

Early on in the project, the pond was essentially a gravel pit which had partly filled with water and become colonised by ruderal marginal plants plus dense floating algae. Obviously this has some wildlife benefit and a few common species of Odonata (dragonflies and damselflies) were seen using it, but the idea was to enhance its ecological value. The green tarpaulin covers a small water pump as the pond is used for irrigation when necessary - something that will continue as the habitat develops.

The pond, April 2011

Over the 2010/2011 winter, many of the ruderals were removed, along with the blanket of algae. The second photo shows that the sides have also been reprofiled, and on the right is an area which has been sown with native wild flower seeds suitable for a stony substrate - behind these (off-photo) are rows of native fruit and nut trees. Some of the ruderals remain or will be allowed to return - after all, nettles (Urtica) and docks (Rumex) are important for many invertebrates - but this work should provide greater biodiversity. However, there's only way to really see how effective such conservation work is, and that is to monitor what lives there. Sounds like an excuse to rootle about for invertebrates...

Although mid-April is a little early for Odonata, on 16th April there were two exuviae (skins) of nymphs that has crawled up marginal plants and emerged as adults.

An exuvium - but which species?

The relatively small size (approx 15mm long plus another 5mm or so for the caudal lamellae at the end of the abdomen which have stuck together) and narrow form make this a damselfly rather than a dragonfly, and so I headed for the excellent little book by Cham (2009). Given the early time of year, there aren't many possible species and I was guided by which I had seen last year. So, I soon came to the Large Red Damselfly (Pyrrhosoma nymphula). This species is relatively stout for a damselfly nymph/exuvium and matches the photo very closely - it has relatively long wing sheaths and a short abdomen, and the back of the head has a rectangular shape (ignoring the central dent).Before emergence the femora would have faint dark band and the lamellae would usually have pale markings but these have now disappeared. I haven't seen this year's adults yet, but at least I know they are probably around somewhere.

A variety of other invertebrates are present at the pond - whirligig beetles (Gyrinus sp.), pond-skaters (Gerris sp.), honey bees, some as-yet unidentified diving beetles, springtails (Collembola) and wolf-spiders (Lycosidae, especially Pardosa sp.) on marginal stones, and water snails; however it is the flies (Diptera) that currently appear to be most diverse (or at least most obvious).

The first recorded this year was a pair of craneflies Tipula vernalis, a spring species mating on a small remaining patch of floating algae in late March. Soon after in April, the bee-fly Bombylius major was noted, along with others including the non-biting midge Chironomus anthracinus, the hoverfly Rhingia campestris and the moth-fly Boreoclytocerus ocellaris though it's worth noting that some of these need collection and closer examination to identify them with certainty. Moth-flies are certainly under-recorded and it's worth getting a copy of Withers (1989) if you are interested; it's currently available for just £4.

Tipula vernalis, busy making more craneflies

Male (plumed antennae) Chironomus anthracinus

The moth-fly Boreoclytocerus ocellaris

The hoverfly Rhingia campestris showing the long rostrum

There's already more (with a few more pics below), but I think initial indications are good - a wide range of colonists already this year to supplement the species persisting from before conservation works on the pond. It is unclear what impact the current dry spring weather is having, though the pond is likely to have some hydrological connection with the nearby River Itchen so hopefully water levels won't get too low. Anyhow, further updates will follow - until then, enjoy the following:

A honey-bee Apis mellifera; a very orange form, maybe the Italian strain?

Tadpoles of common frog Rana temporaria, plus a water snail

References

Cham, S. (2009). Field Guide to the Larvae and Exuviae of British Dragonflies. Volume 2: Damselflies (Zygoptera). British Dragonfly Society, Peterborough.

Withers, P. (1989). Moth Flies. Diptera: Psychodidae. Dipterists Digest 4: 1-83.