The Butterfly Bank: First Year Account

By Sue Ashton

Common Blue male

North Curry Community Woodland at White Street Sports Ground is a great place for summer grassland butterflies. As the trees are still relatively young (planted in 2009), and the ground was originally sown with a mix of grasses and wild flower species, this site (of about an acre) is now home to good numbers of Large and Small Skippers, Meadow Browns, Ringlets, Gatekeepers and even some Marbled Whites in the summer months. Occasionally, Common Blue, Brown Argus and Small Copper butterflies have been seen, but 2016 and 2017 were poor years for them despite the presence of the nectar plants bird’s-foot trefoil, common knapweed, field scabious and betony at the site.

Small Skipper in the grasses of the Community Woodland site

So when, in October 2017, an extension to the car park at White Street Sports Ground meant that spare soil was going to be dumped on the area of grassland between the woodland and the football pitch, it seemed a good idea to use the spoil to make a south-facing and therefore sunny ‘butterfly bank’ and provide a new habitat for butterflies, bees and other pollinators at the Community Woodland.

Butterfly banks have been done successfully elsewhere: for example, by the Shakespeare Birthplace Trust at Mary Arden’s Farm (https://www.shakespeare.org.uk/explore-shakespeare/blogs/butterfly-bank/) and by the RSPB on a large scale at Winterbourne Downs in Wiltshire (https://ww2.rspb.org.uk/Images/winterbourne-downs_tcm9-405356.pdf). Butterfly Conservation has a factsheet on how to create a butterfly bank (https://www.warwickshire-butterflies.org.uk/downloads/Factsheets/Butterfly%20Bank%20Factsheet.pdf) so there was plenty of useful advice for us online.

Our finished bank is about 18m long by about 7.5m wide, narrowing at each end, and is about 1.3m high, with a south-facing slope of about 30 degrees. The soil from the car park extension was mainly topsoil so we covered this with subsoil from a pond excavation and added limestone chippings to a section of the front of the bank (an area of about 22 square metres) as the plants we hoped to grow prefer poor or chalky soil. We would like to have done more to reduce the fertility of all of the bank, but our resources were limited and so we focused most attention on the front of the bank. 

Bank showing area of chippings ready for seeding in October 2017

Bird’s-foot trefoil was the main plant sown on the front of the bank in October 2017 as it is both a nectar plant for adult butterflies and the larval food plant of Common Blue. We also bought common rockrose, the main larval foodplant of Brown Argus, but it was decided to grow this on as plug plants and these have not yet been added to the bank. Other seeds sown were meadow cranesbill, lesser trefoil, black medick, wild marjoram and self-heal. A small quantity of sheep’s sorrel, the larval food plant of Small Copper, was sown along the bottom of the bank, although this plant is already on the site in reasonable quantity. 

The plants that did best were bird’s-foot trefoil and self-heal and the bank was a riot of yellow and purple the following summer. Lesser trefoil and meadow cranesbill were also in evidence, though the black medick and wild marjoram were less obvious. Other flowering plants, however, such as field poppies, mayweed and thistles, arrived by themselves.

Butterfly bank in June 2018

The first butterfly recorded on the bank was a Large Skipper on 14 June. By 25 June, brighter orange Small Skippers had joined the Large Skippers nectaring on bird’s-foot trefoil. The first Common Blues recorded on the bank were two sparring males on 7 July. Meadow Browns were also seen using the bank, generally nectaring on the purple flowers of self-heal. 

Small Skipper nectaring on bird's-foot trefoil

Meadow Browns using the bank nectared on self-heal

During July, there were usually up to three male Common Blues at any one time on the bank, with generally fewer less-obvious females, though two females were observed egg-laying. 

Common Blue male on self-heal seedhead

The first Brown Argus on the bank was recorded on 15 July, and thereafter one or two Brown Argus butterflies were routinely seen. The peak day for the bank was probably 3 August when no fewer than six male Common Blues were recorded with at least one female, along with three or four Brown Argus. On this day, around the rest of the site (an area of about an acre), three or four male Common Blues, a female Common Blue and a Brown Argus were also seen. 

Brown Argus male on bird's-foot trefoil

Numbers began to tail off towards the end of August, and it was perhaps disappointing that Common Blues disappeared from the site while they could still be seen at nearby North Curry Meadow. Overall, the butterfly species seen on the bank were Large and Small Skipper, Meadow Brown, Common Blue, Brown Argus, Marbled White and Large White (the latter two mainly nectaring on self-sown thistle).

Marbled White on self-sown spear thistle

The butterfly bank did not succeed in attracting Small Copper. This species was not recorded anywhere on the site in 2018, although it was seen at nearby North Curry Meadow. The hot, dry summer meant that many plants set seed early and there was little in flower later in the season when Small Copper might have been expected. It is likely that there were not enough nectar plants of the right sort at the right time to attract Small Copper.

 

Small Coppers at nearby North Curry Meadow in September 2018

The flowery meadow mix sown on the back and sides of the bank was not a success. The seed was a grass-free mix that comprised lady’s bedstraw, meadow buttercup, oxeye daisy, red campion, ribwort plantain, selfheal, rough hawkbit, yarrow and yellow rattle. It germinated rapidly, but the species that predominated was ribwort plantain, which proceeded to take over the bank, despite attempts to weed it out. We are unsure whether this was a fault of our chosen mix or the fertility of the soil, but we are removing patches of plantain in order to re-sow these areas and will be adding further chippings to the eastern end of the bank in order to impoverish the soil for the planting of common rockrose.

Flower mix growing on the back and sides of the bank in April 2018 with plantain predominating

The weather will undoubtedly have played its part in the success both of the flowering plants and butterfly numbers in the first year of the bank where a cold spring was followed by a hot, dry summer. It was noticeable that many flowering plants at the woodland had a short season. This probably also affected the numbers of grassland butterflies at the site which were generally down. Large and Small Skippers appeared to fly for a shorter time, and Gatekeepers were noticeably fewer in number. Very few Peacock and Small Tortoiseshell butterflies were seen, although Red Admirals and Commas were present on hedgerow ivy in the late summer and autumn, as well as a migrant Painted Lady. Numbers of Common Blue and Brown Argus butterflies, however, were definitely up on the site, and it is possible that the butterfly bank played a part in this success, although these butterflies appear to have had a good year elsewhere too. 

The front of the butterfly bank in July 2018

Butterflies, of course, were not the only insects to benefit from the butterfly bank. A variety of bumblebees and beetles were observed, and Meadow Grasshoppers and several species of spider colonised the bank. The webs of Four-spotted Orb Weaver spiders could be seen strung between plants, with the resident weaver positioned at the edge of the web, ready to wrap up and carry off any hapless grasshopper that unwittingly jumped into it.

Four-spotted Orb Weaver Spider in web on the bank

 

One of many Meadow Grasshoppers on the bank

  

The front of the butterfly bank therefore performed well in providing a resource for many insects and in particular for increased numbers of Common Blue and Brown Argus butterflies. It seems, though, that we will need to rethink our strategy for helping the Small Copper, perhaps by providing more nectar sources later in the season. We will need to keep improving the flowering plants of the woodland in general, and the butterfly bank in particular, in order to provide more nectar sources for butterflies, bees and other pollinators throughout the year. 

Thanks

We are very grateful to North Curry Garden Club for the kind donation that enabled us to purchase seed for the butterfly bank and other areas. The welcome addition of a National Lottery Community Fund award will allow us to purchase more limestone chippings to improve the soil balance of the bank.