Raft Spiders and Water Crickets

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By Russell Wynn, 1 December 2015

It was another mild night, so while having a break from the laptop I ventured into our Brockenhurst garden to see if there was any nocturnal activity in the pond. Although it is now a few years old, our small patch of aquatic real estate (roughly 2×6 m) is still capable of producing surprises. For example, one night this spring, I spotted the scaly head of a male Great Crested Newt poking out, a behaviour never shown by any of the regular Palmate Newts. Great Crested Newts are a conservation priority in the UK due to habitat loss, but are still relatively abundant in many of the larger New Forest ponds. Nevertheless, it was great to get one on my home turf.

On this early December night I swept my headlight beam across the water surface, and quickly identified a few of the usual suspects: the head of a Common Frog, a juvenile Palmate Newt resting on submerged weed, and a scattering of tiny Water Measurers around the water’s edge. Beneath the surface, Water Boatmen, Black-Bellied Diving Beetles, Water Slaters and Great Ramshorn and Wandering Snails scurried and slimed their way amongst the weed.

More surprising, given the late date, was the continued presence of two juvenile Raft Spiders Dolomedes fimbriatus. These fantastic creatures, one of Britain’s largest spider species, have been a continuous presence in the pond since they first arrived in the late summer. They typically perch on vegetation at the water’s surface, with their legs resting on the surface skin to detect vibrations of nearby invertebrate prey items (and occasionally even tadpoles and small fish). The New Forest is a national hotspot for this species, which is largely confined to wet heathland and boggy habitats in southern England.

 

Raft Spider

These two Raft Spiders were photographed in my Brockenhurst pond in early autumn 2015; note the front legs resting gently on the water surface to detect vibrations from potential prey. The unbanded form (lower image) is relatively uncommon.
These two Raft Spiders were photographed in my Brockenhurst pond in early autumn 2015; note the front legs resting gently on the water surface to detect vibrations from potential prey. The unbanded form (lower image) is relatively uncommon.

 

However, the highlight of this particular night was a ‘first-for-the-pond’ record of Water Cricket Velia caprai, especially as it was of the winged form (which is apparently rather rare). These tiny insects, no more than 8 mm long, resemble a small Pond Skater but are squatter in shape with small white spots on the folded wings. As well as having a chemical deterrent to deter hungry fish, they can also spit on the water surface reducing the surface tension and allowing them to travel up to twice their normal speed!

 

This image shows a winged Water Cricket on the water surface (top), and two Large Red Damselfly nymphs below the surface.
This image shows a winged Water Cricket on the water surface (top), and two Large Red Damselfly nymphs below the surface.

 

This abundance of pond life is highly unusual for early December, presumably due to the exceptionally mild weather during November and the scarcity of overnight frosts (UK Met Office data indicate that it was the third warmest November on record). Nevertheless, it reinforces the ability of even a modest garden pond to attract a wide range of rare and scarce species from the surrounding forest, and the benefits of occasionally peering in to this hidden world during the hours of darkness.

Finally, as I returned to the house, I saw two individuals of another impressive spider species that has recently invaded the exterior of our cottage, but more on that later……

 

Further information about Raft Spiders and Water Crickets can be found at the links below:

http://srs.britishspiders.org.uk/portal.php/p/Summary/s/Dolomedes%20fimbriatus

http://www.naturespot.org.uk/species/water-cricket

 

 

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