Why Do Some Bees Choose to Nest Underground?
Many of the bees you encounter in your garden don't live in large, visible hives. Instead, a significant proportion, estimated to be around 70% of species in the UK, are solitary or semi-social and construct their homes beneath the soil's surface. This subterranean nesting strategy offers several advantages, acting as a natural defence against predators and the elements. The earth provides insulation, maintaining a more stable temperature than exposed nests, and offers protection from heavy rain, wind, and sun. For solitary bees, which do not have a colony structure with a queen and workers, the underground nest is a safe haven for raising their young and storing food provisions, typically a mixture of pollen and nectar.
The choice of location for an underground bee nest is often dictated by soil type and drainage. Bees generally prefer well-drained, sandy or loamy soils that are not waterlogged. Areas with exposed soil, such as bare patches in lawns, sunny borders, or the edges of paths, are ideal. These locations provide easy access for the female bee to excavate her tunnels and cells, and the sunlight helps warm the nest entrance, aiding flight activity. It is vital to remember that these bees are generally docile; their primary focus is foraging and reproduction, and they will only sting if directly threatened or handled.
It's a common misconception that only wasps or ants make underground nests. However, numerous bee species, including mining bees (Andrena species), solitary bees (like Colletes species), and even some bumblebee queens in their first year, opt for this hidden form of habitation. These nests are typically a series of tunnels, with individual cells created off the main burrow. Each cell is provisioned with pollen and nectar, and a single egg is laid before the cell is sealed. This meticulous process ensures that the developing larva has a food source when it hatches, allowing it to complete its life cycle independently.
Understanding this natural behaviour is key to appreciating the role these insects play in our ecosystems. Rather than viewing their presence as a problem, it's an indicator of a healthy garden environment capable of supporting diverse wildlife.
Identifying Common Underground Bee Species
What do you usually see emerging from small holes in the ground during warmer months? It's likely one of the many types of solitary or bumblebees that favour subterranean dwellings. While identifying specific species can be challenging without close examination, understanding the general groups helps appreciate their diversity. Mining bees, genus *Andrena*, are a large group, varying in size and colour, often appearing in spring and early summer. They are typically hairy and robust, with distinctive facial features.
Colletes bees, often called plasterer bees, are another common sight. They are known for lining their nest cells with a cellophane-like secretion, hence the name. These bees are usually medium-sized and have a more uniform, less fuzzy appearance than many bumblebees. Bumblebees, particularly queens in their first nesting attempt or smaller colonies, will also excavate burrows, often in old rodent holes or under sheds, creating nests just below the surface. Their recognisable fuzzy bodies and distinct yellow and black (or orange/white) banding make them easy to spot, though their nests remain hidden.
It is important not to confuse bee nests with those of wasps. While some wasps also nest underground, their behaviour differs. Social wasps like yellowjackets and hornets build large, papery nests, often in voids or underground, and can be more aggressive if their nest is disturbed. Bees, especially solitary types, are generally not territorial around their nest entrance and are more interested in foraging. If you see numerous small holes appearing in a patch of bare soil, especially on a sunny bank, it's a strong indicator of solitary bees, a genuinely beneficial presence in the garden.
The most crucial aspect of identification from a gardener's perspective is recognising that these are bees, vital pollinators, and not a pest to be eradicated. Their presence signifies a healthy soil environment and a thriving ecosystem right beneath your feet.
Managing Underground Bee Nests: Coexistence and Prevention
The presence of an underground bee nest is a positive sign for your garden's biodiversity, but you might still wish to manage their location for safety or aesthetic reasons. The most effective approach is coexistence. These bees are typically active only during daylight hours and are most prevalent in spring and summer. During autumn and winter, the adult bees die off, and only the larvae remain in their cells, overwintering until the following spring. This means any nest activity is temporary, lasting for a single season.
If you have concerns about nests in high-traffic areas like children's play zones or pathways, the best strategy is to deter bees from nesting there in the first place. Promoting a diverse range of ground cover, such as established lawns, ground cover plants, or mulched beds, reduces the amount of bare, exposed soil that attracts nesting bees. If a nest does appear unexpectedly, avoid using pesticides or insecticides. These chemicals are harmful to bees and other beneficial insects, and can disrupt the delicate balance of your garden's ecosystem. Instead, consider cordoning off the area temporarily or simply being mindful of the nest's location.
The goal is to foster a garden where pollinators thrive, understanding their natural cycles and behaviours to ensure mutual benefit.
If you must discourage nesting in a specific, unavoidable spot, consider covering the area with thick vegetation or ground cover plants from early spring, before nesting activity begins. For established nests, especially those involving bumblebees, relocation is rarely feasible or recommended due to the complexity of their underground colonies and the stress it would cause the insects. Accepting their presence and observing their activity from a safe distance is often the most harmonious solution. Educating family members and visitors about the importance of these bees can foster a greater appreciation and reduce unnecessary fear.
If you find numerous small holes in bare soil in spring, avoid digging or tilling the area until late summer or autumn, once the bees have completed their life cycle, to protect overwintering larvae.
Alternatives to Traditional Beehives
While many people associate bees with large, managed hives kept by beekeepers, the reality of bee populations is far more diverse. For individuals interested in supporting pollinators without the commitment of beekeeping, several alternatives focus on providing habitats for solitary and bumblebees, many of which nest underground. Creating dedicated 'bee hotels' or 'bug hotels' can offer shelter, though these are primarily for cavity-nesting species like mason bees or leafcutters, which use pre-drilled holes or tubes rather than excavating soil themselves. However, the principle of providing safe havens extends to encouraging natural underground nesting sites.
A more direct way to support underground nesters is through habitat enhancement. This involves cultivating a garden that offers suitable conditions. Planting a variety of native wildflowers provides a consistent and diverse food source throughout the season, which is crucial for the health of bee populations. Allowing patches of your lawn to grow longer, or leaving some areas of bare, well-drained soil exposed, particularly in sunny spots, can create ideal nesting grounds. This is particularly beneficial for species like mining bees. Ensuring good drainage is paramount, as waterlogged soil can drown developing larvae.
Consider the broader garden ecosystem. Features like compost heaps can provide warmth and shelter, and leaving dead stems on certain plants can offer overwintering sites for some insects. While not directly for underground nesters, a healthy garden supporting a range of insects benefits the overall environment. If you're interested in specific bumblebee species, you might consider creating small, undisturbed mounds of soil or even providing an old, empty rodent burrow, perhaps under a hedge or shed, where a queen might establish a nest. These methods focus on providing naturalistic environments rather than artificial structures, aligning with the bees' innate preferences.
Ultimately, the most significant contribution you can make is to create a bee-friendly garden. This means reducing or eliminating pesticide use, providing a continuous supply of nectar and pollen through diverse planting, and allowing natural habitats to flourish. By understanding and accommodating the needs of bees that nest underground, you can play a vital role in supporting these essential pollinators.