Sunday, May 6, 2012

Assassins on the Pond Surface



Even though there was a frost last night and the pond surface briefly froze, there were two pond skaters Gerris lacustris out hunting by mid-morning, on the lookout for any small insects that had become trapped in the surface film .....



..... like this one. At this time of year most of the prey items are small but in summer I've sometimes seen pond skaters descending like a pack of wolves on drowning wasps.


This one, with a nightmarish countenance, has caught a small fly whose wing you can see held between the short front legs of the predator.


The pond is currently suffering from an algal bloom which slows down the skaters' progress across the surface and sometimes clogs the microscopic hairs that makes these hunters water-repellent. They are spending a lot of time grooming the algae off their body surface and when they do this, grooming the second leg against the third leg on each side in turn, they use one of those short prey-capture legs at the front as the third leg of a tripod to support themselves - normally, when the animal is on the move, the front legs are held just above the water surface. The greenish-yellow deposit on that middle leg on the left-hand side in the picture is a patch of algal cells that the insect hasn't managed to remove yet.


At the moment there are only two pond skaters present and the larger one, top left, is the female. They seem to be courting, by slowly approaching and extending a middle leg towards each other. They breed in May so she'll be laying eggs now and by the end of the month I'm expecting to see nymphs scooting across the surface.

6 comments:

  1. As usual, masterful photographs of often overlooked drama. Absolutely fascinating. We both think your blog is of the highest order.
    Pete says he has spent a lifetime on riverbanks and lakes and never seen pictures of those skinny legged assassins doing what they do. Though he has observed a small fly sticking the nut on a wolf spider and the spider wimped out and ran off. Arachnids don't always have it their own way!
    We wonder what camera equipment you used for these outstanding shots.

    ReplyDelete
  2. Thanks for the kind comments snippa.I took them with an old Nikon D70 DSLR (I'm saving up for something with more megapixels) and a Tamron 180mm. macro lens. with is designed for use with a 35mm. film camera, so with the small digital sensor it's effectively a 270mm. macro lens. It's a heavy, cumbersome lens that's awkward to use, hard to hold still and has a shallow plane of focus unless the light is good and you can stop it down, but it gives really nice out-of-focus backgrounds and you can keep well away from wary subjects, without disturbing them. Weighs a ton though, so I mostly use it in the garden - wouldn't want to carry it far!

    ReplyDelete
  3. Wonderful photos of these fascinating aquatic creatures.

    ReplyDelete
  4. Thanks for the camera information.
    Pete was tickled by your description of the "old" D70. He has an OLD Nikon FM with a Vivitar 28/200 on the front - that's a lump! He reversed his Vauxhall over it and it emerged unscathed. Build quality or what?
    We might have a play with DSLR soon.

    ReplyDelete
  5. Not sure some of the modern cameras would stand up to that kind of treatment snippa. I used to have an Nikon FE that was built like a tank ....

    ReplyDelete