Bug hunting and number crunching!

If you are under the impression that bug hunters are an odd bunch… well, you’re absolutely right! Picture a Sunday morning, 7am in the inner London borough of Wandsworth. Hardly any traffic and I’m standing bleary-eyed outside my house waiting to be picked up by Andy, my partner in crime (well… at least when it comes to aquatic bug hunting). We have been monitoring two sites since December last. The first at Ravensbury Terrace and the second at the confluence of the Graveney and the Wandle.


The ‘Wands’ currently monitor 10 sites along the river and collaborate with the Environment Agency and Riverfly Partnership in the overall monitoring of the abundance of river fly life.

I get picked up and we head for Ravensbury Terrace, the scene of the Wandle Trust’s May cleanup. It’s a lovely sunny day, the water is nice and clear and there is the odd Olive fluttering around.

Donning our waders (a most unusual sight in Wandsworth) and waddling over to our usual site, we start our sampling.


Basically, it’s an evenly split three-minute kick sample, using a kick-net (a heavy duty pond net), ensuring that we cover the different features found at this stretch, namely weed and gravel, both in slow and fast water. We then empty the contents into a bucket, remove any unwanted objects, wash the sample and then sort through it. This is done by emptying out the contents into a white tray and then extracting the target invertebrates (bugs to you and me) using a turkey baster type instrument into a segmented white tray.


We then simply crunch the numbers and come up with an abundance score. This is relayed to the Environment Agency, who record our findings and investigate fully if we report a major decline in species or abundance. The target groups are as follows: Caddisflies (both cased and caseless), Up-Winged Flies (Mayfly etc), Stoneflies and Freshwater Shrimp. On the Wandle we have all groups except Stoneflies. Pictured below are a Blue Winged Olive nymph, a Damsel Fly nymph, a Caseless Caddis and an Olive in all its glory.

Blue Winged Olive  Green Damsel Nymph

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Numbers crunched, we then check the fly boards that we have positioned at various selected points in the river (these are normally covered in brown patches, which are the eggs, predominantly of Olives) before heading off (just in time for the tea and biscuits!) to the Wandle Trust’s clean up. The bottom line is that the riverfly monitoring has given both Andy and me an insight into the Wandle’s invertebrates, their cycles and environmental needs. It has also intensified our relationship with the Wandle and is something I’d recommend to any angler on any river. If you are interested in becoming a monitor on the Wandle, please contact Will Tall through the Riverfly tag at the top of the page.

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