In spring and early summer, you may notice bees coming and going from holes in walls or the ground. These are probably masonry bees (also called mortar bees) or mining bees. They resemble honeybees, but they don’t produce honey or beeswax. They are solitary bees, but don’t be confused by that term. “Solitary” in this context means each female is fertile and will build her own nest, collect her own food, and lay her own eggs. Many of these types of bees may live near each other, but the difference is that these bees do not live in a hive, they don’t swarm, and they generally don’t sting. They are non-agressive. Males have no stinger, and females will usually only sting if handled roughly. These bees, being very good pollinators, are helpful to have around.
The general life cycle of these bees is that larvae from the previous year, which have overwintered in the nest, will pupate and emerge as adults, usually in the spring. The males generally emerge first and wait for the females so they can mate as soon as the females emerge. The males die after mating, and the females begin building their nest and preparing a food source for the eggs they will lay. Some of the eggs will be fertile, and will develop into female bees; the others will be infertile and will develop into male bees. In preparation for egg-laying, females will make several pollen-gathering trips, and this is when you are likely to see them. They’re generally only active for a few weeks every year while they’re gathering pollen and nectar. After laying their eggs, the females die. The eggs hatch into larvae and the cycle begins anew.
Masonry bees will nest in holes in the ground as well as in existing holes in soft stones or bricks and loose mortar, with a preference for south-facing locations. They may enlarge these holes slightly, which can sometimes cause structural damage to buildings, but normally the holes aren’t very deep.
Female masonry bees fill the holes with nectar and pollen before laying an egg in it and sealing it. These bees nest in spring and summer, laying anywhere from 2 up to as many as 12 eggs in sealed cells, depending on space available in the hole. When the eggs hatch, the larvae will feed on the stored pollen and nectar and remain in the cell over the winter. They pupate in spring and emerge as adult bees in the summer.
There are approximately 20 species of masonry bees in UK, with the Red Mason bee being the most common.
Mining bees nest in the ground in loose soil and are commonly seen in lawns. There are many different species in the UK. One of the most frequently-noticed is the Tawny mining bee, which stands out thanks to its furry, reddish-brown body.
Mining bee nests usually look like a volcano-shaped mound with a hole in the centre about the size of a pencil. Sometimes these are built in lawns, and sometimes under stones and pathways. Some mining bees prefer to nest in sandy, south-facing ground, while others like clay more than sand. The bees build tunnels under the mound, and depending on the bees, tunnels can be as deep as half a meter. Eggs are laid in compartments off the main tunnels.
There may be several mounds in an area, or sometimes mining bees will even share an entrance, but this is not indicative of a colony, as each female has her own tunnel. Like masonry bees, the females collect nectar and pollen to provide a food source for the eggs they will lay inside their nest.
Mining bee nests won’t harm gardens and the mounds soon disappear, as most species of mining bees are only active for a month or so in the Spring. Their larvae remain underground for the rest of the year and will emerge as adults the following spring,
Control of masonry and mining bees is usually not necessary. However, if masonry bees are causing structural problems, the best time to carry out control is in late autumn, when the females are no longer around. Then the holes can be filled so they won’t be reused the following spring.