Required reading for river managers

There’s a widespread movement to fence livestock out of rivers – it seems to make intuitive sense where there are a lot (and I mean a lot) of cows and sheep in fields next to rivers, and they’re kicking up a lot of sediment into the water.

But there are two sides to this story and this article – British Wildlife: fencing of rivers is not ‘good for biodiversity’ by three of Britain’s most respected wildlife biologists – should be required reading for everyone in watery nature conservation.

What’s this got to do with ponds? Well, pond, streams, rivers and lakes are part of a continuum of habitats that shelter our freshwater biodiversity. But more directly, light trampling is a natural part of the ecology of all freshwaters – something we noted a long time ago in an article called ‘New approaches to pond management‘, which you can read here (page 284 has the discussion about trampling).

Of course, the intensity of trampling that goes with modern livestock densities is probably not a good thing. But equally, fencing all rivers is not the ideal solution either.

At this rate, maybe one day we’ll have to write a ‘New approaches to river management’ article too!

Backswimmers don’t just eat mosquitos – they scare them off too

Although backswimmers (our four species of Notonecta) have a bit of a popularity problem because they can bite, they will probably redeem themselves in many people’s eyes for eating mosquito larvae.

Now, new research suggests that, as well as eating the pesky larvae, they may also simply scare mosquitos away with great smell of backswimmer – because the mosquitos can sense chemicals released into the water by backswimmers, and avoid laying their eggs in these places.

I’m intrigued by these results as, just now, I have no backswimmers in any of my ponds – as a result of the summer drawdown and, I suspect, a dense cover of duckweed on the old pond – but I do have quite a lot of mosquito larvae. And up until water levels dropped this summer (and in the case of the New Pond, disappeared completely), backswimmers have been a regular feature of the ponds, and mosquito larvae have been a rarity.

It’s just possible this new research explains why.

So for the mosquito-ly challenged, how do you go about attracting backswimmers? One might assume it wouldn’t be too difficult, but in the Abingdon garden pond survey they were only found in about a quarter of the ponds, so there’s no guarantee you’ll get them.

They don’t seem to need all that large ponds – we found them in one Abingdon pond that was only 0.7 square metres, and they were abundant in one that was three square metres. Some open water looks important, and they probably avoid ponds completely covered in Lemna. They don’t need terribly deep water – until recently there was no shortage of them in my old pond which has a maximum depth of only 25 cm.

So that shouldn’t be too difficult, though many ponds will struggle with the amount of Lemna, if this turns to be an real requirement.

To read the mosquito work in detail, the paper is here although only the abstract is free to view; if you e-mail the authors they will usually send a free pdf of the full report.

Just in case you’re wondering (as the Telegraph is not quite sure), backswimmers are sometimes also called Greater Waterboatmen.