Gardens: Expect the unexpected...again!

I thought last week’s Brown Hairstreak butterflies were the end of the rarity excitement in my garden for the year.

Not that rarities are everything, you understand – there is much pleasure to be had from the common stuff. But the ‘unusual’ does add a bit of frisson – and by 'unusual' I mean something that you hadn't expected to see rather than it being a hyper rarity nationally.

In some gardens, a visit by some Long-tailed Tits or a Brimstone butterfly might be out of the ordinary. Such events are always a useful prompt to think, ‘They’ve made it here once, so now what could I do to make it enticing for one to stay and set up home here should they come again?”

Well, this week’s surprise in my garden turned out to be this:

I’ve had lots of species of dragonfly and damselfly visit, but never this one.

You know the rule that dragonflies hold their wings open like an aeroplane whereas damselflies hold their wings closed behind their back like a closed book? Well, there is one group of damselflies that ignores this rule. On the continent they’re aptly called the ‘spreadwings’ but in the UK they are typically known as the emeralds.

And this is a Willow Emerald. The tell-tale marks are the pale dots towards the end of the wings – these markings are called pterostigmas, which sounds very grand, but all that means is ‘wing marks’.

This was not a damselfly in my field guides when I was a kid. The only individuals that had ever been recorded in the UK were in 1979, 1992 and 2007. But then in 2009 over 400 were seen in a big (and natural) invasion from the Continent. They have since spread and can now be found across most of eastern England up to Yorkshire and are still spreading west.

And they have a fascinating behaviour of laying their eggs in tree bark overhanging water. The eggs don’t hatch until spring, and the tiny larvae are programmed to high-dive into the water below. How bizarre is that?

So, finding adult Willow Emeralds is a case of looking for them, usually between July and October, warming themselves up on the sunny side of trees if you have them overhanging your pond.

The two curved 'pincers' at the very tip of the abdomen show that this is a male - you can see them clearly in the second photo. So unless a female wanders by, too, my garden won't be producing any of its own Willow Emeralds next year. But what a subtle stunner.

And as this is a damselfly that is spreading so quickly, there is every chance that your garden could host one this autumn, too, in your own tale of the unexpected.