I find it very hard to love a Cabbage White butterfly but there are many others I enjoy seeing on my allotment. Among my favourites are the four blue butterfly species which are to be found on the ancient chalk grasslands of the Whitehawk Hill Local Nature Reserve along the boundary of our allotment site. These are the Common Blue, Adonis Blue, Chalkhill Blue and the Small Blue, which is Britain’s smallest butterfly and has the delightful scientific name of Cupidus minimus.
While the adult butterflies feed on nectar from many flowers, the caterpillars have very specific food plant requirements. Of these four butterflies, the Common Blue caterpillar has the broadest diet, eating Birdsfoot Trefoil, Common Restharrow and clovers. The Adonis Blue and the Chalkhill Blue caterpillars need to feed on Horseshoe Vetch and the Small Blue caterpillar feeds on Kidney Vetch. In turn, these plants have specific habitat needs, thriving on chalk grassland.
Adonis Blue – Chalkland Blue -Common Blue – Small Blue
This specialisation of food plant makes the butterflies very vulnerable to habitat loss. In Britain 97% of chalk grassland has been lost since the Second World War, mainly to development and to intensive agriculture. The remaining areas are often small and far apart. This means that nationally these species of butterflies have also declined dramatically as their food plants have disappeared. If an area of chalk grassland is lost to development it is often too far for the butterflies to fly to the next area of suitable habitat and so they die out.
So I decided to try and increase the area of habitat for them by growing the plants that these butterfly caterpillars need on my allotment. In the three years that I have been growing these plants I have had small numbers of these four blue butterflies visit my plot and seen the females egg laying on the plants.
As well as providing food for the caterpillars, the flowers make a colourful carpet which many species of native bee feed on. Most of these particular caterpillar food plants have pretty yellow flowers and Horseshoe Vetch has a lovely scent.
If lots of allotment tenants had a small patch of these flowers it would add up to a lot of blue butterflies! Fortunately, the plant species thrive on poor chalky soil so you can keep the rich improved soil of your plot for your vegetables. The plants do need to be in a sunny situation though to attract the butterflies.
Growing your own plants for attracting blue butterflies
1. Start by sowing seeds of the plant species mentioned above in 3 inch pots to give them a robust start. Then plant them out when they are about 4 inches high.
2. After they have flowered it is important not to dead-head or tidy up the plants as it gives the plants time to disperse their seed and the caterpillars will still be feeding until they hibernate or pupate in the soil in the autumn.
3. To keep these areas looking pretty you can also grow late flowering native plants such as Small Scabious and Wild Basil amongst them – the adult butterflies like to nectar on these later flowering plants.
Where to get suitable seed and plants
- Some of the seed I’ve already collected will be available from The Hub at the next open day (5 September)
- If you don’t feel confident enough to grow your own plants then the Wildflower Conservation nursery at Stanmer Park has a good selection in pots.
For more information
- The Pocket Guide to the Butterflies of Great Britain and Ireland by Richard Lewington is an excellent and inexpensive book with lots of information and beautiful illustrations of our butterflies and their lifecycles.
- Sussex Butterfly Conservation has a good website with information about where to see butterflies locally.
Thanks to Tessa for this interesting article.