Why Irish badgers eat few worms

THERE ARE few certainties in life and even fewer when it comes to wildlife. Badgers in Britain live mainly on worms.

We were sure that Irish ones also ate worms but nobody thought of checking to see if this is actually the case. Now, some ground-breaking research by Gráinne Cleary, at Trinity College in Dublin, has turned our ideas about badger diet on their heads. Irish badgers don’t eat that many worms.

Badgers are opportunistic feeders, eating anything which happens to be available, from berries to bulbs and baby birds. Even hedgehogs, with their armour of sharp spines, are not safe from the badger’s powerful jaws; curling up in a ball is no defence when Broc is around.

In Britain, 75% of the stomach contents of badgers, examined at post mortem, consisted of earthworms. A British badger may consume over 200 worms during a night when feeding conditions are good. Worms come to the surface to feed on detritus and they like mild damp conditions. Badgers are experts at predicting where worms will appear and seem to forage using their acute sense of smell. Worms are easy to catch when the grass is short and so the climate and farmland of Britain are ideal for badgers. Ireland’s conditions should, on the face of it, be rather similar if not better, as far as worm-hunters are concerned, but Cleary’s research suggests that this is not the case.

Badgers are being killed in the vicinity of farms where bovine TB has been detected. Cleary has been collecting the carcasses of these unfortunate animals and examining their stomach contents. To her surprise, worms hardly featured in the diet of the animals which she has examined so far. Badgers here, she says, display “seasonal specialisation,” that is to say they eat different things at different times of the year. In the spring, the big attraction is leatherjackets. These are the larvae of craneflies, the familiar daddy-longlegs, an insect which is attracted by artificial light and enters houses in summer and autumn. Known to the cognoscenti as “tipulae”, there are at least six common daddy-longlegs species here. Their larvae live just under the soil, feeding on the roots of grass. They can, occasionally, be so numerous as to create bare patches in fields and leatherjackets are a major agricultural pest. By eating huge quantities of them, badgers are helping the farmer.

The tipulid larvae become adult insects during the summer, so badgers must look for another source of food. According to Cleary, larger creatures such as frogs, and the nests of bees and wasps, now become the main attraction. The nests are mostly those of solitary bees and wasps. Of Ireland’s 91 bee species, 71 are solitary. We have only six social wasps, the ones with which people are familiar, compared to 53 solitary ones. Bees and wasps become scarce in autumn and so the badgers must change their diet again. Now it’s the turn of moths, particularly the caterpillars of yellow-underwing moths. We have at least five species of these glamorous insects in Ireland. Some underwing caterpillars feed in trees and shrubs, others eat grass. The larvae of the large yellow-underwing will feed on almost any green plant.

The finding that badgers eat few worms here may seem unremarkable but it has some fairly profound implications; an animal’s choice of diet may impact on its lifestyle. It had been suggested, for example, that the complex social organisation of badgers in Britain is the result of their predilection for worms and the super-abundance of this prey. Badgers in southern Europe and in Sweden have social systems which are more typical of other mustelids, the family to which badgers, along with otters, stoats and pine martens, belong. Female mustelids, as a rule, hold individual territories. Males have larger territories, which overlap those of the females. Southern European badger populations have a similar distribution and many live in pairs. Significantly, worms do not feature much in badger diet in these warmer countries; the soils are often too hard for worms to be easily harvested.

In Britain, however, badger society is based on communal “sets” with several males, females and their offspring living together in an extensive network of underground chambers and passages. There may be up to 10 adults, as well as cubs, in a typical set and up to 25 adults have been recorded. More than one female may breed each year and a litter may have several fathers. The basis of the system is thought to be the super-abundance of worms in Britain. There is so much of this food available that the population density increased to levels which would not longer support a distributed population and so the animals opted for communal living. Cleary’s research now calls all that into question and casts doubt on some cherished ideas of Irish badger life.

So how many badgers live in your typical Irish set? Up to now, we thought that there would be several adults just as there are in England. There may be enough daddy-longlegs and moth larvae to support such extended groups here but it is also possible that there are fewer badgers in a typical Irish set. At this stage we just don’t know. This would be another interesting topic for Cleary and her colleagues to investigate. Send any badger observations you may have to Gráinne; [e-mail].