Creating a limestone bank for butterflies

25 August 2013

It’s always nice when something you plan works out well, and I’m pleased with the limestone bank we built in the garden last year.

The inspiration for it came from Jan Miller-Klein’s book “Gardening for butterflies, bees and other beneficial insects” (http://www.7wells.co.uk/index.asp). In it, she recounts how she created what she termed a “moraine garden” in order to introduce the sort of poor quality, alkaline conditions that some wild flowers need.

We have difficulty doing much with one side of our garden, as it was a rubble roadway for lorries for some 30 years, and when the land was sold back to our property, it seems all the did was shove down a bit of topsoil over it, meaning that strip is topped by a mixture of soil and (lots of) rubble, under which is compacted subsoil. Most things planted there tend to go a very funny colour, I guess because some nutrients are locked up by the compactions, and refuse to grow for a couple of years, after which they either get going or expire.

The bank under construction

We started making the bank by putting down a membrane, to discourage the bindweed, though I had some concerns that it might stop some of the plants putting their roots down deeply enough: a problem which doesn’t seem to be occurring. On top of that we put whatever rubble we could lay our hands on, including some dug out of the garden and a contribution of broken tiles from next door. We then bought some limestone chips and some limestone “dust” to make the top layer. One thing we rapidly learnt was that fine limestone, once wetted, sets very hard! Planting the wild flowers I grew from seed in the greenhouse was an interesting experience: I’ve never had to use a hammer and chisel to plant something before!

I’ve so far planted kidney vetch, harebells, bladder campion, bird’s-foot trefoil, rock rose, black medick and (recently) field scabious. None of them had any more nutrients on planting than the soil they were grown in, but they are all flourishing. They are getting a bit too rampant in places, actually, which is amazing.

Limestone bank in flower. Yellow in foreground is kidney vetch, while the yellow behind it is bird’s-foot trefoil. The white is bladder campion, and in the foreground you can just see the blue of a harebell.

My reason for creating the bank was to make use of a difficult area, allowing me to grow some of the limestone-loving wild flowers I think are very attractive. There was always the vague hope that a butterfly or two would be attracted: most of the Blues like plants like this. Most Blues would not be found in a garden, but the Common Blue was always a possibility, and one male actually turned up yesterday and found the bank. Whether a female will find it and lay eggs is considerably more dubious, not least because these butterflies don’t just need certain plants, they need ants as well, with which they have a symbiotic relationship: the caterpillars produce a sweet liquid which attracts the ants, and the ants provide some protection to the caterpillar in return (with some species the ants even take the caterpillar into their nest, where it eats the ant grubs!). I have seen black ants on my limestone bank, but goodness knows if they are the right ants.

Common Blue – background shows the limestone bank

So, the bank has done its job and allowed me to grow some attractive flowers and they have attracted a Common Blue. Whether I’ll ever get them breeding remains to be seen, but it’s fun to hope. It is very possible I’ll get some moths using the plants for their caterpillars – my challenge will be in spotting them.

How to identify your butterfly – size

6 April 2013

When people tell me they’ve just seen a Common Blue, or a Small Copper, the one thing they always say in a surprised tone of voice is “it was really small” – which is true for these species and others. I think this is one of the things that is not immediately obvious in many of the butterfly identification guides: they usually state the size of the butterfly by giving its wingspan, but that doesn’t have the instant impact of seeing, say, a Common Blue next to a Red Admiral.

This shows a Red Admiral with a Common Blue superimposed on it to show their relative sizes.

Swallowtail with Small Blue superimposed

Our smallest butterfly in the UK is the Small Blue, whose wingspan may be as little as 20mm, which is about the size a 1p piece is across – think about it! The largest is the Swallowtail at 85mm – which is nearly 5 x 1p pieces side by side. You are, however, unlikely to see either of these butterflies unless you know where to go looking for them. Species you are more likely to see vary from the Common Blue, Holly Blue and Small Copper (all around 35mm) to the Red Admiral at 70mm. If you see a blue butterfly in your garden it is almost certainly the Common or Holly Blue – the others need rather specialist habitats.

You do not generally get very different sizes of the same butterfly: a Silver-studded Blue is always small and a Red Admiral is always large – though there will always be exceptions, as this is the natural world, not something machine-produced. An adult butterfly – the one with wings – stays the same size from when it emerges from its chrysalis to when it dies. All the growing is done in the caterpillar stage, when the insect needs the sort of nutritious food that helps you grow, which is to be found in leaves, stems etc. The adult drinks nectar for energy to fly and mate, but does not need food for growing – imagine that, a lifetime of eating nothing but the equivalent of chocolate! Unfortunately, it’s also a very short life in this stage.

One of the books which does help you understand the relative sizes of adult butterflies is “Philip’s guide to the butterflies of Britain and Northern Ireland”, published in 2007. The photos on the main pages are sized to fit the space, but at the beginning there are drawings of all the members of the various butterfly families shown at their relative sizes. The other publication which does this is the FSC fold-out laminated guide. Both of these publications are sold by the Dorset Branch of Butterfly Conservation on its sales stall – go to the website to find out where the stall is to be: it appears at many events throughout the County.