British populations of butterflies, including some of the most familiar countryside species, will begin disappearing within decades unless we take action. This is the alarming conclusion of new research published in Nature Climate Change by a group of British scientists.
Butterflies are naturally sun-loving creatures, and with the UK sat on the northern edge of many species’ ranges, previous studies have forecast possible benefits to UK populations from a warming climate. However, as the climate changes, extreme weather events including droughts are expected to become more common. Droughts can be a problem for butterflies, especially if they harm the plants upon which caterpillars rely for food. With less food around, populations can crash, and may take several years to recover to pre-drought levels.
The new study used models to predict the frequency of droughts like that of 1995 under different scenarios of greenhouse gas emissions, and examined factors affecting the likelihood and speed of recovery for populations of six species of butterflies that experienced population collapses after the 1995 drought.
While droughts as severe as 1995 have previously only occurred as little as once in 200 years, allowing plenty of time for butterfly populations to recover, the study found that they may become far more frequent. If greenhouse gas emissions continue to increase at current rates, they might even occur on average once every 1.29 years (effectively every summer).
Under “business as usual” scenarios, the research forecasts the widespread extinction of local colonies of butterflies as soon as 2050. So, what can be done to conserve our butterflies? Here is my simple, three-step guide:
Step 1: stop global warming in its tracks
Clearly, reducing the impacts of climate change will be important. Delegates from around the globe will meet in Paris later this year for the 2015 UN Climate Change Conference, hoping to reach the first deal on reducing emissions since Kyoto 1992. Under the study’s best case scenario for emissions, 1995-like droughts might occur only every six to seven years, giving butterfly populations much more opportunity to recover in between.
Step 2: protect butterfly habitats
Ensuring the availability of suitable habitats for butterflies can also make a big contribution. The researchers found butterfly populations were more likely to persist through droughts and recovered more rapidly if situated in areas with larger, less fragmented patches of semi-natural habitat, such as grassland. Larger areas are likely to contain more abundant and diverse food-plants, helping more species of butterfly, and can also better resist edge effects associated with drought, such as moisture loss from woodland.
Highly fragmented habitats have more edge relative to their area, and therefore experience more severe edge effects. Well connected habitats, through which butterflies can easily mingle and locate breeding sites, could add decades on to the survival of certain populations as the climate warms.
Step 3: create more butterfly-friendly gardens
While large-scale habitat management programmes, such as the establishment of nature reserves, are an important means to preserve semi-natural habitat, the restoration of connectivity is where butterfly enthusiasts can help at home.
According to Richard Fox from the charity Butterfly Conservation, many drought-prone species can be encouraged to breed in gardens by leaving grass to grow long. “You don’t have to let your prize lawn go to rack and ruin, you can just leave a strip along the fence”, Fox told me. Depending on how much is left, this could provide breeding habitat for species including the speckled wood, ringlet, meadow brown and large skipper.
Meanwhile, other species can be helped by choosing garden flowers with care, or letting them choose themselves. “Large and small white will breed on Nasturtiums and love to nectar on flowers like buddleia and perennial wallflower,” advises Fox, while “green-veined white caterpillars can feed on lots of weeds, so not being too tidy can help”. If you have a garden, why not plant some butterfly-friendly plants of your own?
So while butterfly lovers will be among those waiting with bated breath for the outcome of the Paris summit, they may also be able to help closer to home. Habitat availability will be vital to the survival of butterflies when drought strikes, and by providing such refuges in back gardens anybody can help them survive and flourish.