A butterfly’s view of the Royal Canal

Don’t dismiss that patch of nettles as ‘weeds’: it is prime butterfly habitat

The last refuge of nature in our overcrowded world is often, ironically enough, to be found in obsolete remnants of human industry.

Our canal system is a monument to Victorian engineering, but these artificial waterways no longer carry commerce from town to town. Meanwhile intensive farming, with its pesticides, herbicides and fertilisers has, biologically speaking, impoverished the soils of the agricultural land around the canals. So the pathways and hedgerows alongside their banks have inadvertently become sanctuaries for the great variety of wild flowers that can no longer survive in industrialised grazing and cereal systems.

One of the last places in counties Dublin and Kildare where you can still find the characteristically rich plant life of calcareous (limestone-based) grassland is along the banks of the Royal Canal. And with these plants come a host of associated life-forms, from butterflies to birds, once abundant in these landscapes, now often also reduced to these accidental arteries of biodiversity.

The idea that the natural world is a web, in which everything is connected to everything else, lies at the heart of ecology and has become commonplace in our nature education. But there are myriad interlinked strands in this web, and many of them are not at all obvious – until someone points them out to you. Grasping a fresh set of such connections directly is always a special pleasure, and reframes the way we look at familiar places.


Wealth of species

Jesmond Harding is a good man to reframe your view of a canal bank in early May. At first sight, the vegetation is still mostly an unexceptional muddle of green leaves but Harding deftly identifies a wealth of species, linking most of them to the life-cycle of particular butterflies.

Occasionally, the butterfly’s common name will give a clue to one of its host plants. A holly blue appears, flittering obligingly over a holly bush. Harding says that this generation will lay eggs on the holly’s tender fresh leaves, perfect food for its caterpillars. By midsummer, however, the leaves will be too tough. So the next generation will lay on ivy, and the caterpillars will feed on its emerging berries.

Harding is a schoolteacher, and exhibits the best of his profession's ability to rapidly communicate facts through infectious enthusiasm. He has been interested in birds since the 1980s, but more recently became fascinated by butterflies, and helped found Butterfly Conservation Ireland.

So the way he views the canalbank vegetation is focused through the lens of these creatures, extraordinary not only in their beauty but in their two radically different lives, first as crawling planting-eating caterpillars and then as flying nectar-feeders.

One of the few plants already in flower where we are walking the canal bank, near Louisa Bridge at Leixlip, is the cuckooflower, also known as lady's smock. Its variable lilac, pink or white blossoms are familiar in wetlands. I was vaguely aware that it was associated with the orange-tip, a small white butterfly with vividly contrasting wingtips. And sure enough, we see an orange-tip flickering away within minutes of first seeing the cuckooflower. Harding is able to show me exactly where to find the orange-tip's eggs, tiny green ovoids adhering just below the blossom where the seed pod develops.

A few minutes later, we visit the remarkable landscape of a former spa, alongside the Louisa Bridge railway station section of the canal. This is a Special Area of Conservation, and is rich in wetland plants such as bog cotton, the carnivorous common butterwort, a small galaxy of bogbean in spectacular bloom – and more cuckooflowers.

Above them, a green-veined white butterfly dips and rises. Harding explains that this species also uses the cuckooflower to host its eggs – and to feed its caterpillars. But it lays eggs not on the seedpod, but on the rosette of leaves at the base of the plant. This is an example of “ecological separation”, whereby neither butterfly need compete with the other.

Nearby, Harding identifies two speckled wood butterflies engaged in what I have always taken to be an elegant, spiralling courtship dance. But Harding gently corrects me. These are two males, disputing territorial rights. “They have no biting body parts,” he says, “but they can knock scales off each other’s wings.”

Everywhere along the bank, Harding identifies more plants whose leaves (or berries) feed caterpillars, or whose flowers provide nectar for butterflies – meadowsweet, restharrow, meadow vetchling, wild marjoram and many more. You might dismiss that patch of nettles as “weeds”, but it is prime butterfly habitat.

A peacock butterfly settles nearby to feed on an elderflower in the hedgerow. Harding thinks it’s a female from its size. To check, he tosses a small stone, so that its shadow moves rapidly over the leaves near the butterfly. It does not stir.  “Definitely a female,” he says. “A male would have taken off in pursuit of the shadow, hoping to find a mate.”

When you see a butterfly fluttering over flowers without pausing to feed, he says, it is usually a male, searching for a female freshly emerged from a chrysalis. The females may emit a pheromone – a chemical signal to indicate their presence – but this has still to be confirmed by science.

The male has to be quick off the mark, because the female will usually only mate once in her life cycle. A single batch of sperm will enable her to lay successive sets of eggs over the next few weeks. Harding says, however, that there is some evidence now that some females mate twice, and that those that do may live longer; food for thought, perhaps.

But even as Harding reveals the multiple quirks and connections of the web of life around us, he expresses anxiety that this rich and threatened ecosystem is threatened by the plans of a State agency, Waterways Ireland, to "improve" public access to the canal banks. His concern is shared by walkers and nature lovers along the Barrow and elsewhere. This issue, and Waterways Ireland response, will be the subject of a future article on this page.

Love butterflies? Help their habitats!

Butterfly Conservation Ireland was born 10 years ago when some birders ran into some butterfly enthusiasts in the bogs of Kildare. They were quickly – and happily – infected by their passion. Together, they decided to form the first Irish group dedicated to butterfly conservation.

Essentially, this means conserving habitat favoured by their food plants. “Our love of butterflies led to our love of the places where they live,” says Jesmond Harding. He adds that butterflies are a great flagship species for conservation generally, because most people find them very attractive, even when they know very little about them.

The group now manages two sites for butterflies, one on an organic farm in the Burren, another on Lullybeg Bog, Co Kildare, partnered by Bord na Móna.

“Conservation management often means scrub clearance,” says Harding. Abandoned habitat is often not good habitat. Direct intervention is often necessary, reviving traditional practices like coppicing trees.

You can also do lot for butterflies in a small garden. Harding recommends limestone gravel for growing devil’s-bit scabious and bloody cranesbill, and a patch of grass, mowed only very early in the season, with common knapweed and bird’s foot trefoil. Avoid exotic plants, he says, you certainly don’t need buddleia or rhododendron, which easily escape and may quickly monopolise nearby native habitats.

The group also organises walks and lectures, and records species as citizen scientists. See butterflyconservation.ie/wordpress