ANOTHER LIFE:'TINY WASPS ARE known whose larvae parasitize the larvae of still other kinds of wasps that live inside the bodies of the caterpillars of certain species of moths that feed on certain kinds of plants that live on other plants."
Edward O Wilson offered this tangle in The Diversity of Life as an ultimate in customised dependence among the myriad parasites of nature.
They include, of course, the large community of organisms – skin mites, bacteria, fungi and sometimes worms and lice – adapted to live on or in the human body.
Some parasites do ultimately kill their hosts, as in the microscopic nematode worms bought by many organic gardeners to control pest insects. But most succeed in eating their hosts sustainably – “one small piece at a time”, in Wilson’s phrase. In the case of the lampreys of our rivers and lakes, the human distaste for their method doesn’t quite spoil the interest of their lives and history.
In Co Limerick just now, at the Annacotty bridge on the River Mulkear, a tributary of the Shannon, one apparently stands a good chance of watching dozens of sea lampreys building their nests with stones on the riverbed below. They can move quite large ones, twice the size of a fist, with the suckers beneath their noses. These circular mouths, studded with rasping teeth, have a certain disturbing likeness to the giant machines that bore tunnels, such is nature’s inspiration to engineering design.
Petromyzonidae, or “stone suckers”, is actually the lampreys’ family name, but the mouth is also used to excavate blood and muscle tissue from the flanks of fish met in rivers or sea – mostly merely wounding but sometimes grinding too far. Thus, in one part of the world, lampreys can be prized and conserved as a vulnerable wild species while in another they are reckoned a devastating plague.
The fascination begins with their place in evolution. The eel-like lampreys, too slippery to hold, are jawless fish. And while near relatives are the hagfish – squirming bundles that recycle dead whales on the deep seabed – lampreys have backbones of cartilage, which make them vertebrates. Indeed, the jawless fish, Agnatha, are reckoned the oldest vertebrates of all, emerging on the evolutionary tree hundreds of millions of years ago, precursors of the human form.
Ireland has three species of lamprey – sea, river and brook, in descending size – and while in England they have been eaten, even to the fatal surfeit by Henry I in 1135, it took the EU habitats directive to generate much interest on this island. Commanding special areas of conservation for lampreys, it has warranted river-by-river studies for the National Parks and Wildlife Service, with electrofishing, snorkelling and radio tracking.
Only sea and river lampreys are anadromous, moving between the ocean and their spawning grounds in rivers; the smaller brook lampreys were cut off by Ireland’s postglacial rise. As in Europe and Britain, the main hazard to lamprey populations here is weirs and other obstacles between estuaries and spawning rivers. Their larvae spend up to eight years buried in silt and feeding on diatoms.
Along with parts of the Suir, Nore and Moy, the lower Shannon is especially important for sea lampreys. The Annacotty stretch of the Mulkear is the focus of monitoring and conservation, even to the point of building special passes at the weir. The website mulkearlife.comgives the story of a remarkable venture to conserve not only lampreys but also otters and salmon. Lampreys do sometimes chew on laggardly salmon but balance things out ecologically by cleaning up gravel for the salmon to spawn on in autumn – for this, go to shannon-fishery-board.ie/catchment/beautyandbeast.htm.
The story across the Atlantic is strikingly different. Sea lampreys, native to North America’s east coast rivers, have become an invasive species in the Great Lakes. Reaching them through shipping canals in the 1920s, they have preyed heavily on commercial fish stocks and left anglers complaining of catches “like Swiss cheese”. The US government spends about $14 million a year on chemicals, traps and electric barriers in spawning streams and releases thousands of chemically sterilised males to engage in unproductive mating.
Lampreys are perfectly good to eat – think of smoked eel: delicious – and both Sweden and Finland have major fisheries for river lampreys, caught in basket traps on migration upstream. The UK had a fishery on the River Severn, and its lampreys once went into the decorated pie presented to the monarch by the city of Gloucester on big royal occasions.
The habitats directive has changed all that, and the lampreys for Queen Elizabeth’s diamond jubilee pie were a gift flown in from Lake Huron. “I’d have sent them truckloads,” said a spokesman for the Great Lakes Fisheries Commission.
In one part of the world lampreys are prized and conserved as a vulnerable wild species while in another they are seen as a devastating plague
Eye on nature
We found the headless body of a thrush on the patio and, the next day, the body of a blackbird – also minus its head. -Tomás McDaid, Sandyford, Dublin
Probably the cat. Blackbirds and thrushes are moulting following the breeding season and are easy prey.
On May 30th my father and I came across a bug in the car park. It was amber in colour with hard wings and what looked like a stinger at the back. - Kevin Cullen, Baldoyle, Dublin
From the photograph you enclosed, it was a cockchafer beetle.
Recently, while walking in oak woodland, we saw a pygmy shrew jumping around manically in front of us, gyrating and tumbling around. Was it diseased or engaged in spring fever? - Larry Gordon, Tallaght, Dublin
Most likely it was suffering from a parasite either externally or internally. Stoats behave like that when a parasitic nematode attacks the brain. And pygmy shrews suffer from endemic shrew fleas that are also an intermediate host for tapeworms.
I drove from Dún Laoghaire to Blessington and back recently, and not a single insect came to a sticky end on my windscreen. My garden is eerily silent too. - Erica Devine, Sandycove, Co Dublin
Be thankful for the absence of midges.
* Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo, or email viney@anu.ie. Please include a postal address
