Tansy Beetles after the Flood

Last Christmas York was seriously flooded. The floodplains around the city were inundated for several weeks afterwards and I wondered what effect this would have on the population of the endangered Tansy beetle, which was hibernating underground. They are known to cope with winter flooding, but just how much is too much?

 December 2015: Water to the top of the floodbank

I survey a section of riverbank each year, recording tansy plants and tansy beetles. My sector was particularly badly hit by the flooding, as the area populated with tansy beetles is confined by floodbanks which kept the water level higher, and for longer, than on the adjacent plain. The main survey period is in late summer, when the new generation of beetles emerge from pupation, but last year I carried out a spring survey as well. This week I've been back to my sector, to repeat the spring survey and see if any beetles have survived.

 May 2016: The same area now dried out

Finding the tansy plants at this time of year is tricky, as they have no flowers yet and the foliage just blends in with all the other riverside plants. However, it didn't take long to find a clump with a beetle on it. Eventually I found a total of 37 beetles on 11 clumps of tansy. This is well down on last year's spring total of 83. However, in the warm weather the beetles were very active, continually appearing and disappearing as they moved around the tansy plants, so I don't place too much reliance on the numbers - just the fact that they have survived here is remarkable.

Spot the tansy plants

Pair of tansy beetles on nettle

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