Solitary bees are a very diverse group of bees, both in appearance and lifestyle. The smallest bees are 3 mm and the largest are 25 mm. They are named after the way they look after their brood. Most species are solitary, which means that the female bee takes care of the nest and the brood by herself. Unlike honeybees and bumblebees, solitary bees do not have a social structure, so we cannot speak of queens and workers. There are more than 500 species of solitary bees in Slovenia, compared to more than 1000 species in Italy.
Different species look for different nesting sites. The best-known species are those that nest in holes in wood or hollow plant stems. But many also nest in the ground, in rock crevices, on stones where they build their nests out of mud and sand, and even in snail houses. Females carry a food supply of pollen and honey into their nests and lay an egg. This is the end of the female's care for her offspring. The egg develops into a larva, which eats the food supply and pupates. The bees overwinter as a cocoon and fly out the following year.
Solitary bees are very efficient pollinators. They collect pollen mainly for the brood's needs. Mostly they collect it on their heavily bruised legs and/or on the underside of the rump. Unlike honeybees, which carry pollen in a clumped form, solitary bees carry pollen in a powdery form, so more of it falls on the flower. A single solitary bee therefore pollinates many more flowers than a honeybee. Because many species are small and not as conspicuous as, for example, bumblebees and honeybees, they are easily overlooked. But it is these bees that are key to maintaining plant biodiversity. That's why protecting them is so important. We can help by keeping meadows, borders and gardens colourful and flowering, so that they have enough food and nesting opportunities in the environment. The construction of nest boxes for solitary bees is also becoming increasingly popular.
You can make your own nest boxes. They can be made from natural materials such as hollow plant stems (bamboo, reeds) or wood in which holes are drilled. It is important that the holes are 3-9 mm in diameter and up to 15 cm deep. The holes must not be drilled all the way through, as one side must be closed. The nest boxes are installed in spring, as this is when most species are active. It is important that it is placed in a sunny position protected from rain. The nest box should be placed at least one metre above the ground. It should also be left outside over the winter.
Prepared by the National Institute of Biology
Photo from Blaž Koderman
