Crop circles in Wyre!

Ian Wallace writes: “While looking for caddis larvae in Wyre on the 8th April this year I noticed several small bulls-eye circles, about a centimetre across, cut through the fine silt layer on the top of a submerged stone at the mouth of the Park Stream (SO 7547 7661).  After a bit of thought I realised I must be looking at the marks left by one of Wyre’s commonest caddis, Agapetus fuscipes. The larva has flat ended mandibles that scrape over the rock surface to detach diatoms, algae and organic silt which they swallow as food. One of the greatest problems for the larva is to avoid being swept away by the current, so they always have one end of the case anchored to the rock by a few silken threads. That enables them to pivot round the anchor point, the bulls eye of the marks, as they feed. They might only work part of the circle. After clearing an area they will then attach the free end of the case before detaching the original anchor so they can swing round to make a little forward progression. There has to be just the right combination of silt depth and current speed and density of individuals for these mysterious circles to appear, made by little Agapetus as it harvests its crop of diatoms.”

Agapetus fuscipes feeding marks, Park Brook, 8 April 2016 ©Rosemary Winnall

Agapetus fuscipes feeding marks, Park Brook, 8 April 2016 ©Rosemary Winnall

Live Agapetes fuscipes showing evidence of grazing, Park Brook, 4 May 2016 ©Rosemary Winnall

Agapetus fuscipes, Wyre Forest, 21 April 2016 ©Rosemary Winnall

Agapetus fuscipes outside case, Wyre Forest, 21 April 2016 ©Rosemary Winnall


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