By grubbing up hedgerows and the thick tangle of wild flowers and grasses round the edge of fields, farmers have removed the source of nectar and pollen that insects need. As countryside is swallowed up by expanding towns and motorways, insect habitats are destroyed. Tidy road verges and public spaces that are often treated with insect-killing herbicides are just as damaging. The list goes on.
Some of these causes can be reversed, and gardeners can make a massive difference by growing insect-friendly plants. Individual plots are often tiny, but the total amount of green garden space is huge. In 2003, researchers at the University of Sheffield found gardens comprised 23% of the city space. They also reported that small gardens made the biggest contribution to wildlife biodiversity. Butterflies and bees travel widely and pay no attention to boundary fences.
Plants attract pollinating insects by offering food: nectar and pollen. The former contains sugars for energy, and the latter provides proteins and oils. In exchange, the pollinators fertilise flowers by transferring pollen from flower to flower. We enjoy apples, cherries, tomatoes and courgettes thanks to the tireless activities of hoverflies, wasps, beetles and many others.
Pollinators add an extra dimension to the garden. Bumble bees are first on the scene in Scotland: you might see six species. And don't knock wasps at this time of year: the queens are as busy in my greenhouse as the bumble bees, preparing the ground for next month's sweet loganberries. Even if you can't resist swatting these industrious queens, small, wasp-like hoverflies should be cherished, since their larvae are among the most efficient consumers of aphids. Like solitary bees, there are as many as 260 species in the UK.
These pollinators don't care if their food comes from a native or imported species but they need certain types of flowers. Shape, scent and colour are what matter. Unfortunately, especially bred "showy" plants are no use to them. The extra whorls of double and multi-petalled flowers replace the male and female parts of the flower and the vital nectaries are minute or non-existent. What appeals to gardeners doesn't always suit the diners. They need single blooms. These can be single flowers, such as daffodils arranged in clusters, like pulmonarias, or bunched together in tightly packed heads, like the daisy family.
Different species need different types of flowers. Butterflies, moths and a few bumble bees, like Bombus hortorum, have long tongues, or probosces, with which to scoop the prize in the likes of lonicera or nepeta. Other bumble bees, such as Bombus pratorum, have short tongues and enjoy open-topped species like verbenas, sedums or hardy geraniums. Honey bees, hoverflies and beetles will also pollinate these flowers. Gardeners should have as wide a selection of flowering plants as possible: that way there will be something for every insect.
It is important to arrange a succession of flowering plants, but spring is a critical time as emerging insects need to quickly build up energy. When visiting the garden centre, look out for flowering plants that suit bees and butterflies as well as yourself. The Royal Horticultural Society (RHS) is compiling a list of suitable plants and asking garden centres to label them. The label features a bumble bee and the words "RHS Perfect for Pollinators". Look out for the labels; if you don't see any, ask the garden centre to join the RHS scheme.
You are spoilt for choice now. Flowering currants and grape hyacinths give emerging queen bumble bees a great start. Popular garden plants, such as Iberis sempervirens and I saxatilis, are good for pollinators and consider single-flowered wallflowers, Erysimum cheiri. Wild cherry blossom near my burn is also alive with bees.
Edible herbs are a good food source for pollinators. Leave chive flowers long enough to let the bees in first; they'll be interested in sage and thyme flowers too. I need every square inch of greenhouse space now, so am pleased to put my flowering rosemary bushes out for the bees.
It helps insects when you arrange plants in groups. They won't see solitary blooms, but will quickly home in on a good blaze of colour. And speaking of colour, insects see flowers differently to us. As a general rule, they see further into the ultraviolet end of the spectrum. Butterflies are supposedly attracted to pinks and purples, while hoverflies are turned on by yellows. n