On the sugar beat

"I CONFESS to a liking for wasps, wrote Robert Lloyd Praeger, the great Irish naturalist, "they are so active and daring, dainty and cleanly." But, sitting down on a mossy bank by the Wood ford River, Co Galway, to admire a meadow full of flowering sisyrinchium, he found himself perched on a big wasps' nest, its humming rising angrily beneath him. What to do? Two swift skips took him head-over-heels into the river and he swam off underwater, drowning five wasps inside his shirt.

Nothing like this seems to happen any more: perhaps there are fewer people of any sort sitting down on ditches. But the in-your-face colouring of wasps and their distinctive engine-note sustains the human interest in their sinister potential. Each summer I am asked for ways of destroying wasps' nests sometimes, it seems, on an unduly precautionary principle.

This month, however, has brought two observations from readers that open graphic little windows on to the social lives of wasps as they forage and feed their young.

Seamus Kennedy, of Donaghmede, was standing under an ivy-covered tree when he noticed "wasps and bluebottles falling down on the ground and spinning around, as if the wasp was attacking the bluebottle. After a while, they would both stop and the wasp would dissect the bluebottle and fly away with half. Another wasp would come down and take the other half. This happened a number of times."

These were adult social wasps, collecting food for the grubs in their nest; the larvae are carnivorous and are fed with chewed-up insects or other protein. The adults themselves usually prefer sugary liquids, high in energy, and visit shallow flowers to lick up the nectar. The congregation of wasps and bluebottles suggests the presence of something dead, perhaps a bird or a mouse. Wasps sometimes feed on carrion juices or bring some back to their young.

The wasps don't sting their prey but pounce on them and bite them. Flies and caterpillars are bitten into pieces for easier transport and there were enough wasps in the raiding party to leave nothing behind.

The grubs in the nest reciprocate by letting the adults lick off their saliva, which contains sugar, surplus to their needs. This curious economy could possibly bear on a wonderfully mysterious observation by a reader at Kilcloon, Co Meath:

"During the long, hot summer of 1995," writes Dervilla McKeith, "some wasps built a nest in a sally tree in our garden. I never saw the nest but the tree was alive with wasps and boomed with their buzzing. A dark, burnt-looking patch appeared on the grass under the tree which seemed to `belong' to the wasps and which gradually increased in size until it was about 10 inches in diameter. This patch seemed to provide an irresistible attraction for red admiral butterflies, which visited it in large numbers.

"The butterflies packed themselves on to every available space on the blackened patch of grass with their wings out-spread, tips touching, so that the whole patch was covered with shimmering colour, like a tiny piece of oriental carpet. At one stage I counted 22 butterflies, with several others hovering nearby, waiting their turn, or so it seemed. On the rare occasion when the sun disappeared behind a cloud, the butterflies all vanished as if by magic and, equally magically, reappeared from no-where when the sun came out again."

Red admirals have quite as sweet a tooth as wasps watch them feeding right beside them at the holes in fallen apples in autumn. The black patch was almost certainly sugar of some sort and a drip from somewhere above seems most likely. Could it have been from the wasps nest? The excessive dribbling of baby wasps does, now I look at it, seem a bit far-fetched, if ingenious of me (indeed, the nest was never actually seen).

Try it the other way round what would attract lots of wasps and provide a drip for the admirals? Honeydew from aphids? Too dispersed, though wasps do sip it. A run of sugary sap from the tree? Some European wasps visit such exudations on oaks but willow's sap carries aspirin-like salicylic acid, not likely to be sweet at all. If the wasps were bees - hive bees gone wild, with a leaking honeycomb? But Ms McKeith said wasps, not bees.

So in the end, I don't know. But what a charming mystery to stretch the mind! It also recalls a momentous discovery in the collecting of specimens from nature which became such an all-consuming hobby for many Victorians and which left us with so many drawers of butterflies, moths, beetles and birds' eggs.

In the early 1800s, when entomology was beginning to be a gentlemanly passion, several collectors noticed that night-flying moths were drawn to sweet things, such as the bottles of sugary water or beer hung against walls in gardens to try to tempt wasps away from fruit. Even better was an empty beehive smeared on the outside with honey.

The squire who made this experiment found the whole exterior of the hive completely covered with moths, sometimes of a score of different species.

"The moths are generally so engaged in sucking the honey as to allow themselves to be easily taken if quietly approached.

"Sugaring" for moths became the standard technique, as collectors perfected their own treacle mixes, brushed on to tree trunks at dusk before the moths emerged. Strong-smelling brown sugar (the real stuff, made from cane, not beet sugar dyed with molasses) was mixed with hot water or beer, sometimes with a dash of rum or even methylated spirits for scenting the night air seductively.

Even today, some moth-hunters keep a special treacle pan and swear by particular recipes. The snag is having to stay up to make regular tours of the patches - the "sugar beat". The mercury vapour light-trap, invented in the 1950s, draws moths to its extremely intense illumination, through a series of vanes that entrap them in a bag for leisurely morning inspection.