The Role of Wild Bees in a Healthy Ecosystem

Quinta Vale da Lama, in partnership with Mud Valley Institute, offers a 6-month residential farm internship to support and create the next generation of organic and regenerative farmers, giving participants the critical learning and work experience as they begin their journey in food grow and farm operations with a focus on project design and management.

Sarah wrote a detailed article which we have turned into three blog posts to be shared with you. This is the first blog in the series.

Buzz, buzz… There’s nothing more curious than the buzzing of an insect in the hollow of a flower. You bend down, curious, and suddenly a large bumblebee emerges, covered in pollen, already looking for the next flower. A few seconds later, the next insect lands on the same petals and starts the process all over again. This long dance of pollinating insects will only end at nightfall, when the flowers slowly close their petals. Dozens, even hundreds, of pollinating insects can land on this flower during the day, most of them being domestic and wild bees.

A wild… bee? Yes, you read that right. We all know the domestic honeybee, but their wild cousins are often unknown. And yet they certainly play a role! Some have metallic purple hues, some have subtle stripes, and some are surprisingly large… wild bees never stop to fascinate. Some are tiny – just a few millimetres long – while others, such as bumblebees, are recognisable by their fluffier appearance.

Whether solitary or living in small colonies, these fascinating species are intimately linked to their habitats through complex symbioses that are still far from being fully understood. Yet wild bees are disappearing in silence as agriculture and urban expansion continue as a result of reduced agricultural production and less resilient and genetically diverse ecosystems. The consequences of their disappearance are severe, especially here in the Algarve, where many cultivated species (tomatoes, courgettes, almond trees…) are partly dependent on pollination by honeybees and wild bees to produce their fruits.

There are around 20,000 species of bees in the world, of which around 680 are found in Portugal. That’s quite a lot, so I’ve written a summary of the general situation of wild bees, with a focus on the Algarve.

I hope you enjoy it!

Wild bees are not domesticated bees that have returned to the wild. They are particular species of bees with some specific characteristics. Let’s take a step back: among the 20,000 species of bees in the world (including the well-known honeybee), bees strongly differ in their degree of sociability, their feeding habits and their nesting behaviour. Socially, some species, such as the honeybee, live in colonies, stocking up on honey to survive the winter, and the queen of the colony is particularly fertile (hundreds or even thousands of eggs are laid during the year). Other species (wild bees) are solitary; and live alone in the nest they have built. They lay a limited number of eggs before dying and leaving their eggs to hibernate.

Not all bees are great architects though, and some species develop alternative skills in imitation and camouflage. They don’t build nests or colonies; they don’t collect pollen or nectar for food… So how do they survive? The answer lies in their name: the parasitic bee. Also known as the ‘cuckoo bee’, they are found in many species of wild bees that have their own ‘associated parasite’. This parasite lays its eggs in the nests of other bees, which, once emerged, feed on the foreign food supply and generally kill the eggs in the nest. This type of parasitic behaviour has a role to play in the ecosystem: it forces the parasitised species to be constantly on the alert and adapt to constant change.

Honey bees, wild bees, parasitic bees… How do you find your way around? By classifying the different ‘types’ of bee into families, then into genus, and finally into species. Although honey bees are the best known and most widely managed pollinators, they represent only one species within a family of bees.

There are 6 major bee families:
– Apidae (including domestic honeybees and bumblebees)
– Colletidae (most species are nesting in the ground)
– Megachilidae (the wild bees build their nests using pieces of leaves or petals)
– Melittidae (many species are endemic to Portugal)
– Andrenidae (these wild bees are nicknamed sand bees because of their tendency to nest in loose soil)
– Halictidae (particularly small bees, often with a metallic sheen)

A great-banded furrow bee (Halictus scabiosae).

To understand the importance of wild bees and their role as pollinators, we first need to understand the principle of pollination.

Pollination is a key stage in the reproduction of plants and trees and can take different forms depending on the type of vegetation. While some crops and trees, such as rice, wheat, oak and pine, rely on the wind to carry their pollen, other flowering plants rather rely on pollinating insects to ensure their reproduction. The principle is simple: when a bee lands on a flower, it collects pollen for its own needs, but it also involuntarily carries a few extra grains on its body, which fall on the next flower it visits, thus ensuring the reproduction of the plant or tree it is foraging on.

Just as the bee needs the plant to feed itself, the plant needs the bee to reproduce. A 2007 study shows that around 80% of flowering plant species in temperate climates depend on pollinating insects for their reproduction (Klein et al. 2007). In semi-arid climates such as the Algarve, both domesticated and wild pollinators play an important role in pollinating local plants, particularly horticultural crops (Haldhar et al 2018). As a result, insect pollinators play an important role in today’s agricultural production by ensuring the reproduction of plants – and thus the production of fruits and vegetables. For example, a 2006 study estimated the global monetary value of ecosystem services provided by wild pollinators at around $57 billion (Losey et al, 2006). In addition, by transporting pollen between different plants and trees, bees also ensure genetic mixing within the ecosystem, making it more resilient to disease or climate change.

But… both honeybees and wild bees are pollinating insects. So why is the wild bee so important for pollination and ecosystem health? The difference lies mainly in the efficiency of pollination. There are three types of pollen gatherers: polylectic bees, which collect pollen from several plant species, oligolectic bees (collecting nectar and pollen from plant species belonging to one genus or family), and monolectic bees (collecting from one single plant species).

Honeybees, which are very numerous due to the beekeeping industry, are polylectic and therefore play an important role in pollinating several crops. However, they tend to remain on one plant species or family for a certain period of time in order to collect as much pollen and nectar as possible while resources are abundant.

Among wild bees, some species are polylectic and others oligolectic, and the combination of the two increases pollination efficiency within the ecosystem. Furthermore, several polylectic wild bee species pollinate a wider range of crops and fruit trees, often over longer periods and in more difficult weather conditions. They can be found on cloudy, relatively cold days when honeybees are unlikely to leave the hive. For example, bumblebees (Bombus spp.) visit flowers at times when honeybees are not active (Gamonal et al 2024). The wild bee Osmia cornuta, on the other hand, has been shown to be much more effective than honeybees at pollinating fruit trees, especially almond trees (Fibl 2016).

A violet carpenter bee (Xylocopa violacea).

As we can see, wild bees play a crucial role in pollinating crops and fruit trees. In Portugal, this pollination role is just as important, since the country produces fruit and vegetables whose yields are largely dependent on external pollination by insects – or at least to produce fruit and vegetables of good size and quality (Wentling et al, 2021). Examples include tomatoes, pumpkins, courgettes and fruits (apples, pears, citrus fruits, almonds, ….).

The Iberian Peninsula and Portugal in particular offer a rich variety of habitats, combined with the advantages of microclimates and relatively mild winters. The Algarve, with its diverse landscapes, has the potential to provide an ecological niche for many of Portugal’s wild bee species. From coastal cliffs and mountains to scrubland, grasslands, beaches, wetlands and forests, with ecosystems different from one another, providing a variety of habitats and thus allowing a variety of wild bee species to find refuge. Within this mosaic of landscapes, each ecosystem offers specific resources adapted to the various species.This great diversity of habitats means that many species of wild bees can be found here. In 2020, around 680 species of wild bees were recorded in Portugal (Wood et al 2020) – and yet they are not so easy to see and identify.

So where do they nest? There are almost as many habitats as there are species, each with its own preferences for nesting sites. Generally speaking, wild bees will choose a sunny, not too humid and often relatively sparse vegetation site. The shape and type of nest will then vary from species to species: some will dig tunnels in the ground, while others will stick their nests to rocks, take refuge in the hollow of a tree trunk or dig rotten wood from a dead branch to make a home.

Some bees, such as the genus Megachile, even cover the bottom of a natural cavity (stem, snail shell…) with petals or leaves to lay the eggs. Nevertheless, sandy, well-drained soils remain the preferred habitat for a large proportion of wild bees, particularly in the Andrena and Halictidae families. In this case, the females themselves dig tunnels in the ground to leave their eggs and a few supplies of nectar and pollen.[SM1] . So next time you go for a walk, be careful: a simple dead wood can often hide a whole world the size of a bee.
Speaking of dead wood, have you ever heard of the carpenter bee?

In semi-arid climates such as the Algarve, wild bees along with other pollinators are key to the reproduction of native plants as well as agricultural crops.

In the second part of this blog series, you will learn about the threats to wild bees and the consequences of their disappearance.

To learn more about Sarah and her work, check out her LinkedIn profile.