Wild Bee Ground Nesting Aids: Sand lenses for ground-nesting species

Key facts in brief

• About 70 percent of all wild bee species in Central Europe nest in the ground, not in hollow stems.
• A sand lens in the garden provides the necessary nesting structure that is usually missing in well-tended outdoor spaces.
• July is the ideal time to create one, as the soil moisture is low and the material is easy to work with.

Creating a habitat for ground-nesting wild bees

When we talk about nesting aids for wild bees, we usually think of holes in wood or hollow stems. However, the majority of species, such as the Common Yellow-faced Bee (Colletes daviesanus) or the Grey-banded Mining Bee (Andrena flavipes), rely on open, sandy patches of ground. These so-called ground-nesting wild bees require sun-drenched, vegetation-free areas with a specific soil composition to build their subterranean brood tunnels. With an artificial sand lens, you can provide a targeted substitute for disappearing natural habitats.

Requirements for the nesting substrate

the material must be stable enough to allow for the construction of tunnels, while at the same time being loose enough for the bees to dig. A nutrient-poor site is essential here.

Step-by-step to your own sand lens

1. Choose the location: Find a spot that receives direct sunlight throughout the day. Shade leads to cold soil, which inhibits the development of the larvae.
2. Excavation: Dig out a hollow about 50 to 80 centimetres in diameter and 30 centimetres deep. Remove all root remains and humus.
3. Layering: Fill the pit with the sand-clay mixture. The clay should be mixed into the sand as a dry powder before the mixture is slightly moistened.
4. Compaction: Tamp the material down lightly. Once finished, the surface must be firm enough not to blow away in a light breeze, but soft enough that a fingernail can easily leave a mark.
5. Vegetation control: Keep the area permanently free of plants. Once a month is enough to gently remove any emerging grasses by hand.

Important protection advice

Strictly avoid the use of chemical fertilisers or herbicides in the immediate vicinity of your sand lens. You do not need a fine-mesh net or a cover; the bees will actively locate their nesting sites while flying. Ensure that you do not use peat-based soils, as these make the ground unnecessarily acidic and jeopardise the stability of the tunnels.

FAQ

• Question: Do I need to cover the sand lens in winter? Answer: No, the wild bee larvae are adapted to our climatic conditions. A cover would trap moisture and encourage mould.
• Question: Why are there no bees coming? Answer: Patience is important. It often takes a season for the insects to discover the new site by chance during their exploration flights and colonise it.
• Question: Can I use normal garden soil instead of sand? Answer: No, humus-rich garden soil is too nutrient-rich and unstable. The bees require lean, sandy-loamy material for stable brood tunnels.

Common questions

Do I need to cover the sand lens in winter?

No, the larvae are adapted to our climate. A cover would trap moisture and promote mould growth.

Why are there no bees coming?

Patience is important. It often takes a season for the animals to discover the site through exploration flights and accept it as a nesting place.

Can I use normal garden soil instead of sand?

No, normal garden soil is usually too humus-rich and unstable. Ground-nesting species require lean, sandy-loamy material.

Main article: Ground-nesting wild bees in the garden: Protecting their habitat