Brian Jones and I headed to the river on Friday evening. In the back of the car we had our fishing gear but also an assortment of fine mesh nets, trays, magnifying glasses, forceps and droppers because we thought it might be interesting to take a few kick samples to see what kind of bugs there were at the bottom of the river.

In the end the fly rod remained in the car because the invertebrates were quite fascinating and we wanted to take a good look at them. I was very lucky to be guided by Brian who knows them all well. After we had kicked the stones and disturbed the bottom and collected the dislodged critter in a fine-mesh net, we deposited the contents into a plastic tray. Soon the tray became a busy metropolis of miniature forms crawling or scrambling or actively darting around. Modest as they may be in size, these are the bugs make up the critical link between the photosynthetic organisms and the larger more familiar animals like the gypsy barbel that I come to the river to catch as well as the turtles and the wading birds and their predators. The whole ecological edifice is built on on a foundation of photosynthesising algae which can coat the stones or produce fine filaments or drift freely in the water column. Then come the various grazers of algae and their pint-size predators and little sifters and strainers and gobblers of tiny fragments of organic material. These were the kinds of things that were darting or crawling around in our white plastic tray.

Brian knows all of these critters like the back of his hand and needed only a magnifying lens to be able to check the finer points distinguishing one kind from another but it was a real learning experience for me.

Most of what we found were the nymphal forms of familiar insects like mayflies and sedges and midges but there were also snails, tiny limpets, flatworms, segmented worms and leeches in there too. In among this lot were also some tiny gypsy barbel fry which were probably the offspring of fish like those we had seen spawning when Brian and I were last on the river a couple of months ago.

Each of these little creatures is interesting in its own right. I was fascinated to hear, for example, that the leeches we were looking at, lacking the mouthparts to feed insects, prey instead on relatively soft bodied bloodworms. One of these leeches itself was quite red in colour. We had a few bloodworms also in our sample. Their distinctive red colour is provided by haemoglobin in their tissue which helps them to steal oxygen that can be scarce resource in the sediment in which they wriggle around.

In the air above the river we saw loosely swarming mayflies. They were very tiny and we managed to catch one in a net to examine it. Brian told me that these were male Small Dark Olives and that the females would later in the evening be attracted to join them. At the time we came across them it was a little early for the evening courtship rituals and the females were nowhere to be seen. They were off in the bushes somewhere doing their hair and makeup. Evening would be their time to show up and when they did the males would each vie for a position on the edge of the swarm to improve their chances of getting lucky. After their eggs had been fertilised those females would make their way into and then under the water before laying their eggs in dense yellow aggregations on the undersides of stones.     

Among the samples we collected the most prominent invertebrates were the caseless caddis (Hydropsychidae), though these were far outnumbered by small mayflies like the angler´s curse (Caenidae). The caseless caddis were the big nymphs that we had seen on our previous visit. These are the size that makes them ideal to imitate and Brian was kind enough to tie me up a half dozen.

Several of the caddis larvae we found had built cases for themselves using small dark stones that they had come across. These were found on the undersides of larger stones. Inside the stone case we were able to see the pupae with antennae curled back waiting for the time when they would make their way to the surface to hatch into the winged adult. I was interested to learn that those caddis nymphs are fishermen just like us. They build a silk net un the undersides of stones which capture organic fragments from the current and funnel them into the “cod end” where the nymph feeds. We were able to see the opening of one such net on the underside of a stone.

Brian tells me that those caseless caddis are not to far away from hatching out and so I must remember to keep an eye open for the adults in a month or so when those slim green riverbed “fishermen” have become fluttering moth-like adults returning to the water to lay their eggs.

Screen Shot 2019-06-03 at 19.25.47

Brian tied me up a number of caseless caddis “hydros” and they are a very good copy of the original. One or two were given an extra bit of flash.