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MANY bee species are in decline across the world, but there are things we can do to help boost their numbers on our home turf.

I have previously covered ways to make sure your garden has lots of flowers for pollinators in order to provide their food sources, pollen and nectar. The key thing is to avoid flowers with “double” blooms, like most roses, where the reproductive parts of the flowers have been converted into extra petals, so they lack nectar.

Another way to help is to provide homes for solitary bees – the majority of bee species in the UK – which make their nests in soil, hollow plant stalks or cavities in brickwork.

If you are in a country where spring is getting going, now is a good time to make some tempting real estate for species such as the red mason bee (Osmia bicornis), as young individuals tend to emerge in April and May in such places. They then start looking for a place to build a nest and lay eggs.

You can buy ready-made bee hotels, although some are badly designed and large ones may encourage too many bees to live close to each other, which . It is also possible to buy “bee bricks” for use in construction, but .

Fortunately, it is easy to make your own bee hotel. One method is to to about . The deeper the holes, the more eggs will be put in each one, so make the cavities as long as possible without breaking through the other face of the log.

Starting at the bottom, the bee will lay an egg, deposit some pollen and nectar, seal it in with mud and repeat. She can lay up to 40 eggs in multiple cavities over several weeks. Another reason to make the holes deep is that woodpeckers may eat the grubs that are closest to the outside.

Another option is a bundle of bamboo canes or hollow, woody plant stalks. These can be wedged horizontally into an old pipe or a large plastic soft-drink bottle with the bottom cut off. The edge of the pipe or bottle should stick out a little further than the canes, to help keep out rain.

With either method, make sure the ends of the canes or the holes drilled into wood have smooth edges, as any sharp splinters could tear a bee’s wings, says , a bee ecologist at the University of Sussex, UK.

Once constructed, fix your bee hotel in a south-facing spot, so that it gets plenty of sun, at least 60 centimetres off the ground. A site on a fence or shed is ideal, as putting it on tree trunks can leave it too shaded.

If you don’t have anywhere for a bee hotel, consider helping out ground-dwelling bees by leaving a patch of dryish, crumbly soil in a sunny spot undisturbed. They will make their own holes in it.

For other projects visit newscientist.com/maker