READER Heather Harrison, of Westgate, Burnley, writes about some surprising night-time visitors to her garden

AT midnight, while emptying the rubbish bin two weeks ago, I thought I would check out the wildlife in the back garden next door where our dustbin is kept.

All was very dark and quiet but the garden snails were very busy.

I counted over 140, mostly on the leaves and branches of a pussy willow, some at a height of eight feet. Some of the leaves had many small green caterpillars on their undersides.

Not a single snail was on the bush next to the pussy willow, an evergreen with strong smelling white flowers in summer, which I have been unable to identify. The pussy willow is now very bare, the snails having decimated most of the branches, many of the remaining leaves having just the ribs left from the onslaught.

On the soil was an attractive red slug about seven inches long. The most unusual sighting was a worm, which was about 12 inches up a vertical wall. I was most surprised as I was unaware that worms could climb walls. As soon as I photographed it with a flash camera, it dropped to the soil below.

This peaceful scene was in stark contrast to an event last Saturday afternoon. My son Brian lives about a mile away. He was working on his newly-acquired car on the back street, when he heard a tremendous thud as something hit the car roof, causing a small dent.

Startled, his head emerged from under the bonnet, and a pigeon glanced off his head and landed on the ground. It attempted to run up the centre of the back street, head bobbing, and wings outstretched, but unable to fly.

He was even more startled when a peregrine falcon dived on to the pigeon, before hopping off to one side, then following the pigeon while dragging one wing along the ground. The peregrine then flew into the air about four feet before landing on the pigeon.

Was the dragging wing a ploy by the peregrine to disarm the pigeon, or do you think it was injured? Is this unusual behaviour by a peregrine or have others observed something similar?

A final note -- I saw a large flock of swifts on September 4 (a little later than the reader in Nature Watch, October 3) at about 8pm.

RON FREETHY replies: I think the evergreen bush is a privet. Anyone wanting to know about snails should buy a copy of Land Snails of the British Isles by AA Wardhaugh.

It has 28 pages with illustrations in colour. I am working to identify the slug and the answer will be in next week's column.

The peregrine's wing behaviour could have two explanations. Firstly, Heather could be right and the bird was pretending to be injured.

When a peregrine is about to kill on the ground it often shakes its wing (called mantling), so that the prey is in shadow and can't see the bird striking.