Lesser water boatmen on the wing

 

Chestnut lesser water boatman (Hesperocorixa castanea)

 

It’s tempting to assume that everything in the pond is shutting down for the winter now and traditional advice has always been that autumn in the pond is simply a prelude to winter: autumn is the time ‘to start to prepare [the pond] for the eventual onset of winter‘ or ‘…a time to ready your pond for winter‘.

This may be true of heavily stocked goldfish ponds but in natural ponds there’s a lot of activity going on both in and above the pond – animals dispersing, beginning overwinter growth or simply seeking their winter and spring nursery grounds.

And on warm days in the autumn there are plenty of creatures on the move – including those flying to ponds which have refilled in the autumn.

Late flying dragonflies are easy to spot. But amongst the creatures looking for a new home, some are less conspicuous and today I caught a fleeting glimpse of one of these in the New Pond – a lesser water boatman.

It was too quick to catch, and there was only one, but it looked like either a Hesperocorixa or one of the species of Sigara (from a distance both types look pretty similar, but with a bit of practice the species can be quite easily identified if you have them in the hand).

It must have arrived recently, perhaps in the last few warm days, as I’ve been watching the pond closely and, with the water now clear, it was pretty easy to see. At the very least it must have arrived since the pond refilled earlier in the autumn.

Quite a few kinds of lesser water boatmen move from pond to pond – though not all. The species that prefer bigger permanent water are not so flightly.

It’s been known since the middle of the last century that there are two peaks of flight activity for these animals: in the spring and again in the late summer and autumn.

The autumn move gives the animals a chance to return to those ponds which have dried out in summer – where they should be safer from predators (usually no fish, for example), and face less competition from other water boatmen.

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3 Responses to “Lesser water boatmen on the wing”

  1. Diana Says:

    Every now and then in the new pond which is pretty bare of vegetation, just one marsh marigold, some very small plants at the margins and some pondweed which has not really established yet, I catch sight of a water boatman – have only seen one which disappears really quickly. We have several smallish beetles and lots of very grey quick moving creatures which I am unsure of identifying. They are a bit smaller than water boatmen but move very quickly through the water. Lots of those. The pond is quite wide but shallow and I am hoping it will not freeze too hard in the winter. Also hoping vegetation will establish a bit more next year. I am a bit worried about leaves falling in, mainly because the pond is shallow. I can see that the leaves are usefully creating hiding places but don’t want them to fill up the two slightly deeper areas completely. It’s obviously a fine balance but at what stage do I start fishing the leaves out?

  2. Diana Says:

    I meant to say I just love the way the water boatmen move!

  3. Jeremy Biggs Says:

    I don’t actually know at what point we should be taking out leaves.

    They’re obviously having a big impact when you can see them close to the surface.

    But an inch or two at the bottom – probably no problem.

    It’s one of the things we need to do more careful studies of in garden pond-sized ponds.

    Best thing to do is keep an eye on the wildlife. They will tell us when there’s too much.

    Jeremy

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