ANOTHER LIFE:Such animals offer an insight into the link between biodiversity and our own health

The tracks at the tideline were those of tiny feet: a sinuous line of marks in the sand, now being licked away by foamy wavelets pushing up the strand.

I am used to seeing tracks of fox scavenging at first light well ahead of me, but this was finer stitching altogether: two little paws together at the front, the others spaced aslant in the length of one wellington-boot print – about 30cm.

The skipping gait of a stoat suddenly sprang to mind, an idea that would have taken longer to arrive some years ago. Among the earliest observations to Eye on Nature was that of a Co Clare naturalist who had watched a stoat circling a little pocket of rock-pool in the limestone shore of the Burren. The tide had left a small fish – perhaps a blenny – locked up in the pool, and the stoat, by this account, had mesmerised it by its circling before pouncing to hook it out.

I was, perhaps, a tad sceptical at the time, but others offered similar stories of stoats haunting the shore for prey or fresh carrion. The beachcombing fox, too, helped my education. And the tracks of the stoat now reminded me of Paddy Sleeman’s island badgers.

Dr Sleeman, a zoologist with UCC, has spent years studying badgers as part of research towards a vaccine to protect them from bovine TB. Among them are animals that have colonised offshore islands – two off Donegal, others off Sligo, Cork and Waterford. The badgers seem simply to have walked to them, on short causeways at low spring tides, and decided to stay, sometimes making their setts in sand dunes. And their food, analysed from droppings, is rich in sandhoppers, crab and other marine life – the reason, perhaps, they wandered out on the shore in the first place.

This is interesting in itself. Badgers are supposed to eat earthworms, beetles and frogs. This is certainly their staple menu on pastures of intensive farming, where cattle and ryegrass dominate the local ecosystem. But Ireland’s mustelid mammal family – of which the badger is the largest, the stoat the smallest, the otter somewhere in the middle – also includes the pine marten, notoriously omnivorous in its food, eating everything from squirrels and birds to berries and bees.

The island badgers are fine and healthy – not one of them with TB. That you might expect from their glorious isolation, remote from dairy cattle. But Sleeman is one of the legion of scientists alert to every nuance of the link between biodiversity and the general health of the world, not least of its human population.

A recent manifesto is the weighty (but attractive and engaging) book Sustaining Life: How Human Health Depends on Biodiversity (Oxford, 2008), in which Harvard Medical School enlisted 100 scientists to spell out the consequences of the current cascade of extinction.

The value of “ecosystem services” to human life, such as clean water, breathable air and nourishing crops, may now be broadly appreciated, but nature’s complexity and fragility are not.

The interplay of biodiversity and the spread of infectious diseases has captured Sleeman’s special interest. Many such diseases are spread by biting insects, such as malaria by mosquitoes, and where biodiversity is rich these have a wider choice of animals to bite. Gabon, in west Africa, still has plenty of trees and monkeys, and the level of malaria is low; Ivory Coast is denuded of forests, and the only biteable primates are people, so malaria is widespread. Haiti and the Dominican Republic offer similar contrasts, even as they share one island.

Ireland’s biodiversity is not half bad, if you count in our migrant birds, our species-rich shore and sea, the newly plumbed genetic inheritance of our native wildlife. Even our diversity of snails, creatures so derided by a certain strain of politicians, can have important agricultural value. In a public lecture now offered on YouTube by UCC, Sleeman explains how the liver fluke, damaging parasite of sheep and cattle, needs one particular snail to host part of its life cycle. With so many snail species available, it meets a lot of failure and so its harmful impact is diluted.

A classic ecological lesson is the story of Lyme disease, a tick-borne illness potentially debilitating in people and now making some headway in Ireland. It is named for a town in Connecticut, in the US, where suburbs expanded rapidly into woodland. The woods originally had 15 kinds of mammal the tick could latch on to but few of which would give them the disease in their blood.

After the woods were invaded by houses and people, the mammals were reduced to one, a mouse that could pass on Lyme disease. Now free of predators, the mice were concentrated in the remaining undergrowth, so were more and more infected ticks. This pattern and its consequences helped to spread the pathogen to people across the north-east of the US – and now, it seems, beyond.

You can watch Sleeman's lecture on YouTube at iti.ms/PTE8F0

Eye on NatureYour observations and questions

I found two dead shrews in my garden, one in the water butt and the other, smaller one on the ground. The larger one had a very large tooth, like a fang; the smaller one had no visible tooth. How did one climb so high as to fall in the water?

David O’Connor Castletroy, Co Limerick

The larger shrew sounds like the greater white-toothed shrew, new to Ireland but found in recent years in Limerick and Tipperary. Shrews can climb and starve if without food for more than a few hours.

The worm-like lad in the photograph I’m sending you has appeared in our house, climbing up walls and curtains. Black and about an inch long, it curls into a ball when touched.

Brendan Foley Enniskerry, Co Wicklow

It is a millipede, Tachypodoiulus niger.

Recently I have seen two grey crows working together to chase a terrified squirrel. At one point a crow had the tail in its beak. Were the crows having fun or hoping the squirrel would stay away in the spring, egg-laying season?

Patrick Davey Shankill, Dublin 18

Probably both.

There is a fox family and wildcat mayhem nightly on the lane, with the odd badger thrown in.

Robin Reilly Washington Lane, Dublin 14

Michael Viney welcomes observations at Thallabawn, Carrowniskey PO, Westport, Co Mayo, or email viney@anu.ie. Please include a postal address