IT WAS great to catch-up with Alan Graham of the Devon Angling Association recently to engage in invertebrate sampling on the River Devon as part of the 'Riverfly Monitoring Initiative'.

Invertebrates are the lifeblood of the river, the bedrock that supports so much else. By regularly assessing their populations, we can keep tabs on the health of the river.

As part of the process, Alan and I were kick sampling on the Devon near Vicar's Bridge to determine the abundance and variety of invertebrates.

The process involves furiously kicking at the rocks and small stones on the river bed, and catching the invertebrates stirred by the flailing boots into a sweep net.

We emptied our haul into an examination tray. At first, we could only see a handful of bugs in amongst the mix of gravel, small stones and weed fragments, but then suddenly the tray became transformed into a wriggling mass of life as a whole host of tiny creatures emerged.

We looked down in a sense of wonderment, for the riverbed that at first glance appeared to be just bare stone and gravel, was packed full of an incredible array of invertebrates.

In the tray were an abundance of mayfly larvae (nymphs), and those of caddisflies and stoneflies, as well as tiny freshwater shrimps and a cornucopia of other life including beetles and worms.

These lifeforms are the engine room of the river, the driving force that supports birds, fish and other creatures.

Trout and minnows depend upon this natural bountiful larder for their very being, both when these invertebrates are in their larval stage, and when the mayflies, caddisflies and stoneflies emerge as fully winged adults.

These invertebrates, however, are much more than just food for other creatures. The benefits they provide are immense including the decomposition and the recycling of nutrients, so important for a healthy and productive environment.

In short, without these mayflies, caddisflies and stoneflies, as well as all the other invertebrates, the river would be a wilderness, a lifeless flow of water draining the land, but doing little else.

I plucked a stonefly nymph out from the tray, placed it on my finger and examined it more closely.

Its body was armour-plated in appearance, protected by a hard exoskeleton, which would prove useful protection from other underwater invertebrates, although I doubt it would be enough to deter a trout.

This stonefly was a good find, for they are especially sensitive to water pollution, so where they occur, all is well with the river.

Like the mayflies and caddisflies, they spend virtually all their life – up to two or three years – living on the riverbed, grazing algae and vegetarian detritus, or preying upon other tiny creatures, depending on species.

Then, they crawl out of the water and moult one last time, unveiling from within this nymphal skin a winged adult fly.

It is a true miracle, and the physiological changes that take place, transforming from one form of creature to another, is a spellbinding wonder of nature.