Nature on our doorsteps: Solitary mining bees

Rosaleen Dwyer is the County Heritage Officer at South Dublin County Council – every week she gives us an insight into the natural heritage around us and the beautiful biodiversity of the plants and creatures.

There is just one native honeybee species in Ireland, and 21 bumblebee species.

There are, however, 77 different species of solitary bees.

Honeybees and bumblebees live in colonies in nests or hives governed by a queen.

Solitary bees live separately, making their own individual nests in which they lay less than 20 eggs.

They then stock this nest with big clumps of pollen mixed with nectar and they seal up the entrance.

The eggs are left to hatch and the larvae to fend for themselves, feeding on the pollen before eventually maturing into new adult insects.

There are four main groups of solitary bees, depending on how or where they make their nests.

These are mining bees, mason bees, carpenter bees, and leaf-cutter bees.

The nests of mining bees can be identified by the volcano-shaped pile of soil around the entrance

Mining bee females burrow holes into light sandy soil.  As she digs, the excavated soil piles up in heaps around the entrance hole, forming a little volcano-shaped pile of earth.

While mining bees are solitary in that they make their own individual nests, some species like to make their nest close to other bees of the same species.

This can result in what is called an aggregation of nests, or in other words, many nests located close to one another.

Because the female needs to leave a plentiful supply of pollen to feed the offspring developing in the nest, she works hard and visits many, many, flowers before she finally seals the nest and leaves.

Honeybees and bumblebees are very efficient collectors of pollen, packing it into moist pellets (pollen baskets) on their back legs.

Some female solitary bees also carry pollen pellets on their back legs.

Others pack pollen into the hairs underneath their abdomen.  These pollen pellets, however, are dry and loose, and they can often break up as the bee flies about.

This means that solitary bees have to work harder to gather enough pollen to stock their nests.

It also means, however, that solitary bees are great pollinating insects, because they drop lots of pollen as they go from flower to flower.