The UK butterfly emergency – could biosolar roofs provide some relief?

We think of butterflies as flying flowers. Decorative delights to make us smile on a summers day. But along with their cousins, moths, butterflies and moths fulfil several important roles in the natural world. Not only do they support plant reproduction through their actions as pollinators. Both adults and lava are important food sources for bats, birds and some mammals.

Crucially, butterflies and moths are key indicator species. They are sensitive to changes in weather patterns, habitat availability and  pollution levels  and so we know, when there are fewer butterflies, that something has changed for the worse.

Dr Richard Fox, Head of Science at Butterfly Conservation, has been quoted as saying: “The previous lowest average number of butterflies per Count was nine in 2022, this latest figure is 22% lower than that, which is very disturbing. Not just that, but a third of the species recorded in the Big Butterfly Count have had their worst year on record, and no species had their best. The results are in line with wider evidence that the summer of 2024 has been very poor for butterflies.”

“Butterflies are a key indicator species; when they are in trouble we know that the wider environment is in trouble too. Nature is sounding the alarm call. We must act now if we are to turn the tide on these rapid declines and protect species for future generations.”

Biosolar roofs are widely promoted for their capability generating sustainable energy from photovoltaic panels. The plants on these roofs are accredited with the vital role of cooling the immediate area in order that the panels work as efficiently as possible.

However, those plants also serve other functions:

• Filter pollutants from the air
• Cool the immediate environment
• Provide aesthetic interest and wellbeing benefits for communities
• Form part of a network of wildlife corridors that allow interbreeding between colonies. Thereby maintaining the genetic diversity that supports survival of the fittest.
• Enhance biodiversity net gain by creating habitat and supplying forage for a wide variety of flora and fauna

Biosolar roofs are an important tool in the fight against climate change and biodiversity loss. It follows therefore that with careful planning, these roofs have the potential to slow the population decline amongst butterflies and moths.

Several factors come into play when specifying plants for a biosolar roof. The GRO Recommendations for Biosolar Roofs  indicates that plant growth habit is important. Vegetation should not cast shade over the solar panels. And, as for all living roofs, the root system must not compromise the waterproofing layer.

From the perspective of butterflies and moths, it’s important to have forage and shelter available for all life stages at crucial times of the year. Shelter for overwintering creatures, forage for adults emerging from hibernation and for developing caterpillars. To add to the specifier’s challenge, most caterpillars are incredibly fussy eaters and will only thrive on one or two plant varieties that are specific to the type of butterfly or moth.

In an ideal world, the vegetative layer of a biosolar roof will comprise a varied plant palette with a long flowering period to provide nectar for adult butterflies and moths, and food for their caterpillars.

Click here for a list of caterpillar food plants. Please note that not all of them are well suited for biosolar green roofs.

It is also possible to add other wildlife friendly features to biosolar roofs in order to support populations. Log piles make great resting places for butterflies and will be used by some for overwintering.

Installing adjacent green walls, provided they do not cast shade on the PV panels, also creates shelter for creatures and allows a greater variety of plants to be grown in the immediate area.

If conditions on any living roof are tailored to support butterflies and moths, it follows that many other species will benefit. Ultimately this will not only enrich our ecosystems, it will have a knock-on effect on food production as many edible crops grown in towns and countryside depend upon insects for pollination.

The food chain is not in the least bit linear, it’s a complex web of microbes plants and animals. All are interdependent and all ultimately provide food for other species. (Even the badger, who has no natural predators in life, will be digested after death by a myriad of mini beasts.)

This rhyme, frequently attributed to Benjamin Franklin, alludes to how seemingly small oversights can lead to massive losses. Let us bear this in mind when designing, specifying and installing the architecture that will serve us for the future.

“For the want of a nail the shoe was lost,
For the want of a shoe the horse was lost,
For the want of a horse the rider was lost,
For the want of a rider the battle was lost,
For the want of a battle the kingdom was lost,
And all for the want of a horseshoe-nail.”