Over-arching beauty of stalactites

A READER contacted me.

There’s a stone bridge dating from the 1840s which spans a stream near his home. He was astonished when he looked under the bridge and found small stalactites hanging from the arch.

This isn’t that uncommon. If the bridge is made of limestone, or at least held together with lime mortar, and there is a constant drip of water through the masonry stalactites will form, provided there is a reasonable amount of carbon dioxide dissolved in the water.

The aqueducts on our canal system are mostly between 200 and 250 years old and made of limestone. They tend to leak a little and there are stalactites under most.

They tend to be quite small and fragile. In limestone caves stalactites have been recorded as growing at 3mm a year, which would give you a substantial object in a few decades, but this is under optimal conditions and the average growth rate is only about one tenth of this.

The fragility is caused by the fact that most stalactites form as hollow tubes, like drinking straws, with the water dripping out of the centre. It’s only when the tube gets blocked for some reason and the water starts flowing over the outside of it that the stalactite can develop as a more robust conical structure. Geologists call them drip-stones, which is a good name.

You, or your kids, can also make DIY stalactites in the kitchen using household items. A saturated solution of baking soda (sodium bicarbonate) is normally used. There are detailed recipes on the internet.

Another reader has contacted me about starlings. She wants to know what’s happened to the huge flocks that used to give magical aerobatic displays near her house.

It’s the same around here. There’s a small lake nearby and starling flocks used to roost in its reed beds and put on spectacular displays late on winter afternoons before settling down. Not any more, though starlings still breed on my land, including a pair behind a loose fascia board over the patio, which annoys my wife as they’re noisy and paint the paving with droppings.

The population of Irish breeding starlings seems to be fairly stable, though the species is amber-listed here. But in Britain and over most of northern Europe there is a sharp decline and they are red-listed. The British RSPB has been monitoring trends since 1979 and by 2012 is reporting a 79% decline. The huge flocks of up to 500,000 birds that used to entertain us were composed of winter migrants from Britain and the continent.

Nature table

The stoat is the smallest carnivore in Ireland and a member of the mustelid family. Large members of this family include the otter and badger and medium-sized ones the pine marten and mink.

They are sometimes called weasels but this name should really be reserved for an even smaller mustelid found in Britain but not in Ireland. They are white below and red-brown above with a black tail tuft. In stoats in Ireland the boundary between the white and brown fur is normally an irregular, wavy line while in stoats in other countries it’s a straight line.

Because of this, stoats here and the Isle of Man are regarded as a sub-species. The largest stoats in Ireland are in the south and size decreases as you go northwards.

They are efficient predators and males will kill adult rabbits which are five times their weight. They are common animals, though numbers fluctuate yearly, and rather secretive and seldom seen except when they’re killed on the road.