Cities and urban spaces for pollinating insects

Many species of pollinator insects such as bees, flyflies and syrphids are in decline, largely due to habitat destruction caused by the conversion of natural land to agricultural fields and urbanisation. Although cities are generally considered less rich in biodiversity than rural areas, new research finds that urban areas may actually play a key role in preserving pollinator communities. Indeed, they are full of abandoned places where there is no management of greenery and which, over the years, have been reclaimed by nature. These places can become a refuge for many animals, creating a heterogeneous habitat with a variety of plant essences that provide them with the nourishment they need. These renaturalised areas, besides serving as a shelter for pollinators, can be used by people to relax, observe the nature and why not, play with children.

But then what are the most suitable places to host pollinators in cities? Let us start with private places, where each individual citizen can contribute to making their city and home a more attractive and hospitable place for pollinators. Examples could be green roofs or balconies with high nectariferous and polliniferous blooms. Many people like to have lots of beautiful, colourful and fragrant flowers on their balconies, so why not harness this passion to increase the biodiversity in the city? This recipe, for example, consists of planting suitable plants such as lavender, rosemary and marigold, while avoiding purely ornamental plant species such as the famous geraniums or tulips.

In the public sphere, however, municipalities can increase green corridors, such as tree-lined avenues and strips of wildflowers between gardens or along roadsides. These places are essential to create a network between green areas, connecting them and allowing pollinators to be able to move around, avoiding confinement in one place. Other urban areas that lend themselves well to the creation of habitats for many pollinators are the large, more or less extensive green spaces such as parks, public gardens or even yards.

The pollinators are many and belong to as many different species, each of which has certain habitat requirements. In addition, different habitats are required for many of them to complete their life cycle. For this reason, it is important to include even very different structures and zones in the design of an area for this purpose. The flower meadows are certainly one of the places most visited by insects. Their wealth of plant species constitutes a fundamental source of nourishment. However, flower meadows are of little use if there are no suitable nesting structures nearby. These may consist of piles of dry branches and stones, unplastered dry stone walls, dead logs and sandy or friable soil. In this context, pollinators have the opportunity to nest in summer, protect themselves from predators and overwinter.

The plants to be preferred are those nectariferous/polliniferous, i.e., able to produce a high quantity of nectar and pollen, essential food for adults and larvae. Here we can employ annual or perennial herbaceous plants, such as poppies, climbers, such as ivy, arbustives, such as rosemary, and large trees such as chestnut. The important thing is diversification: having flowers of different colours, sizes and shapes to allow all pollinators to feed. In fact, many wild bees are specialists, that is, they are only able to feed on one or limited species of plants. Ensuring that everyone has the opportunity to find nourishing resources is therefore crucial to avoid the extinction of certain species. Another aspect to evaluate is the flowering period. Some pollinators are active as early as March, while others are only active in late summer. It is therefore important to plant plants with scalar flowering that alternate during the various periods of the year.

Some positive examples of urban regeneration are the Biodiversity Oases of 3Bee where pollinators find both nourishment and nesting sites. In Milan ten different ones have been placed on private and municipal land with the aim of increasing biodiversity and greenery in the city. These are true ecological niches, hospitable environments for pollinators ranging in size from 0.5 to 5 hectares in which approximately ten thousand new trees and plants have been planted. In addition, the special feature of the Oasis of 3Bee are the technological facilities that are placed within them. Through satellite surveys and acoustic sensors it is indeed possible to monitor the health of the plant area and its guests: the pollinators.