Saturday, 3 October 2015

Willow Emeralds return to Thorpe Marshes

Chris Durdin, NWT Volunteer at Thorpe Marshes

They can take a bit of finding, but it’s been a delight on some recent sunny days to see that Willow Emerald Damselflies are there again at NWT Thorpe Marshes on the edge of Norwich. Early autumn – late August to mid-October – is the time to see them.

Willow Emerald Damselfly, photo by Chris Durdin
A quick recap of the story so far. This damselfly is a recent UK colonist, first found in Suffolk in 2007. It's been at RSPB Strumpshaw Fen a few miles east of us for six years, and a colony at Cringleford found in 2013 has become well-known in the dragonfly world. Previously I said we found them at Thorpe Marshes last year, but it’s just come to light that an experienced observer also saw them here in 2013.

A useful tip is to look for them on a sunny, sheltered spot, on branches or other vegetation over a ditch with at least some open water. But they do have a knack of just melting away out of sight, so the highest count to date of ten damselflies is a minimum.

Ovipositing scars on a small willow,
photo by Chris Durdin
A peculiar feature is how eggs are laid into small cuts made in a thin branch, which leaves a distinctive, regular pattern (see picture). That branch is always over water as the eggs overwinter there and larvae drop into the water in the spring.

I have now found seven branches in various parts of Thorpe Marshes which have this proof of breeding and no doubt there are more, based on where the adult damselflies have been seen. It was a great pleasure to share that knowledge with NWT reserves staff on a recent site visit, so that this autumn’s management work can take the Willow Emeralds into account.

The work has just started a busy phase. Subject to ground conditions, marshes are being cut and ditches managed. Ponds, the ‘flood’ and the gravel pit – ‘St Andrews Broad’ – will be enhanced. None of this of this should have much impact on visiting, but keep an eye out for advisory notices. How lucky for me that my local patch should have the NWT’s expert attention.

Management at Thorpe Marshes is underway, photo by Chris Durdin
The management work at NWT Thorpe Marshes has been made possible by the Lafarge-Tarmac and Norse Landfill Communities Funds.

Chris Durdin leads monthly wildlife walks at NWT Thorpe Marshes. Details of monthly walks on 

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