Monday, May 13, 2013

Walking on the water

My little pond currently has numbers of water striders, Gerris lacustris, skating across its surface.  Like others in the family they use a combination of surface tension and active repulsion from the non wetting body and leg hairs to literally walk on the water.  Well, skate, in sudden jerky movements.  They are not the easiest things to photograph.  Get to the side of the pond and they scatter, skipping across the surface at surprising speeds.  Stay there long enough and they drift back - only to scatter again as the camera moves.  Eventually, though, with patience, enough come within reach to allow shooting.  Though getting them aligned for maximum depth of field while holding the camera and flash bracket over the surface of the water is not the easiest of jobs.

These are not big insects - especially if you discount the long legs.  The first shot was set against a fallen bloom of Camellia 'Cornish Snow', 5-6cm across and only half visible.  So an elongated body about 1cm in length with legs extending out as far again.  As always, click to embiggen the shots.

Gerris lacustris
Males are smaller than females, a common occurrence in the insect world. And, of course, they take no notice of any voyeuristic tendencies in the photographer.  Shameless.

Gerris lacustris.  Smaller male on top.

Gerris lacustris.  Smaller male on top.
Why evolve for this water surface skating lifestyle?  Food.  Plenty of it.  Small insects, even larger ones on occasion, regularly hit the water surface, get trapped by the surface tension and their struggles rapidly attract the water skaters.  In the final two shots the individual skaters have each trapped a small midge and are enjoying their meals.

Gerris lacustris.  Midge for lunch.
Gerris lacustris.  Midge for lunch.
The shots were taken with my standard insect setup of Canon 600D, Tamron 90mm macro and 25mm extension tube, macro flash bracket and single diffused 430EX flash.  It's a combination that works reasonably well and, in this case, was light enough to support over the water for reasonable lengths of time without me risking a watery equipment grave. 

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