For his research, the ecologist spent hundreds of hours on various dykes around Nijmegen. ‘It started with monitoring a large number of dyke grasslands. We recorded which flowers were growing there and which wild bees and bumblebees were visiting which flowers.’ He also analysed the pollen grains on the insects’ legs to study how bees distribute themselves amongst the flowers and to see which flowers were popular. There, he discovered something strange. ‘A greater variety of flowers attracts more insects, and in areas where there are six or seven different types of flowers, you can already see more than 50 per cent of the total increase. But beyond that, there’s a sharp drop-off for wild bees. The number of bumblebees continues to rise with more different flower species, but wild bees are much more selective and their numbers stop growing at that point.’ Nevertheless, the ecologist observed that it is precisely the truly vulnerable, red-list species that only return when there are many more flower species present; they need more.
Red clover and dandelions
The most important thing, says Swinkels, is that those first steps don’t take much effort. As soon as plants such as knapweed and red clover – as well as dandelions and buttercups – start to appear, that alone makes a big difference. ‘Plant diversity is particularly important, for example when it comes to the shape of the flower. Red clover opens up. So an insect needs to know exactly how that flower opens. A buttercup, on the other hand, has a very open flower shape, which is suitable for other species of bees.’ Once those flowers are in place, the number of insects can quickly reach two or three times that found in more barren areas.
But we’re not there yet, warns the ecologist. ‘We won’t get there with just this basic number of flowers. Some endangered wild bees, for example, are very fussy, both in their food preferences and when it comes to nesting.’ Swinkels discovered that, although the absolute numbers stop increasing as rapidly at a certain point, the stability of the community does continue to increase, and it is precisely then that the truly rare Red List species begin to appear. ‘If there are even more species and quantities of flowers, we see that pollinators are better able to share the available food. Instead of visiting many different flowers at once, bees seem better able to choose their preferred species, and there is less overlap in their foraging behaviour. This creates space for the Red List species and could even ensure that flower pollination takes place more efficiently.’
Insect motorways
The ecologist’s research demonstrated that dykes could play a crucial role in the return of certain bee species. ‘Not only are these places where there is space for flowers and nature, but they are also attractive to bees: for example, the slope gets nice and warm in the sun, which is ideal for the development of their larvae. Dykes also act as a kind of insect motorway. If all dykes were covered in flowers, they would form connecting routes between nature reserves, and insects would suddenly have a vast habitat. Let’s see how we can design our dykes to be as useful as possible so that as many insects as possible can benefit from them.’