Bugs in the River

Stone fly nymph.

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​​On Monday, as part of our survey of the river Worth and it’s tributaries, we were out kick sampling. This is a way of finding out what invertebrates (bugs) are living in a river.

Most river flies live as flies for only a short period, sometimes for only a day. However they may live as bugs in the river for over a year before hatching into flies. We want to know more about bugs in the river for two reasons. Firstly a healthy bug population should lead to a healthy population of their predators like Dippers, Wagtails and Trout. Secondly the bugs are a very good indicator of the quality of the river water, they are very sensitive to pollution so lots of bugs means clean water.
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To start the survey we chose two locations, one very close to the confluence with the River Aire and the other on North Beck next to Morrison’s car park.  To kick sample you get in the river holding a fine mesh net in the water down stream then kick the stones and pebbles to dislodge any bugs living under them. The standard method is to do three one minute samples at each location. That is the easy bit, the tricky and enjoyable part is identifying and counting the samples.
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Kicking the sample. Note the rubbish in the beck.

Counting the sample.

Bullhead and heptagenid nymphs.

​The samples at the confluence yielded about 50 Heptagenid nymphs and about 25 Olive (baetis) nymphs. We also disturbed eight Bullheads. I think the Heptagenid is my favourite river bug, they just look so alien, they are known as stone clingers and their flattened body shape helps them to stay put in the current. I understand formula one car designers studied their shape to help with aerodynamic design.

Heptagenid nymph - grows to about 20mm.

There was a marked difference with the North Beck sample, it was teeming with bugs, we estimated that the number of both Heptagenids and Olives was in the many hundreds. Obviously when there are that many counting gives way to estimation. This tells us that the water quality in North Beck is excellent despite the amount of litter that is dumped in it or blows in from Morrison’s car park. It is interesting that even though this site is full of bugs we could not see any evidence of Dippers which we would expect to be feeding on them.

Baetis nymph - grows up to approx. 12mm.

Just a small corner of the North Beck sample tray, how many bugs can you see?

​So why the disparity? We are not sure, it could be just that the two sites have different habitats that support different populations, we would need to sample more sites on the Worth to check that. It could also be that the population in the Worth has not recovered from a major pollution incident in 2018, we need to investigate further as well.

The invertebrate pictured at the top of the blog is a Stonefly nymph from North Beck. We had trouble identifying it because it is a much larger species then we usually get, we have not seen one this size before (about 25mm).
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Sampling in this way is a great way to learn more about rivers and their ecology. It's also a return to childhood and messing about in the water! If you or your kids would like to get involved in this project please contact us.
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​All photographs copyright of River Worth Friends member John Tickner, except the Baetis nymph.