Bee Hotels and Seed Bombs – are they worth it?

Occupied shop-bought bee hotel. You can see the tubes which have been filled with leaves by a leaf-cutter bee.

A few years ago you would have found me at various events at work, helping visitors make bee hotels from wooden boxes and bamboo canes and praising their benefits to solitary bees, or mixing seeds with clay and compost to encourage people to ‘bomb’ their gardens with wildflowers for pollinators. And whilst I did so, I wondered if they really were the answer to saving our invertebrates. There was no doubt that the bee hotels did work, as we had seen many occupied with the holes of the bamboo canes sealed up with mud or leaves. However, there wasn’t any research on whether they were a good idea, at least not that I could find, and the trend grew – there’s now a whole array of insect hotels and seed bombs in most garden centers as well as being found online.

Home-made bee hotel from a mixture of reeds, bamboo canes and a wooden box.

This month, Karin Alton and Francis Ratnieks published a review of these products in the journal Bee World, and considered whether they were beneficial or just another trend. Below I look at some of their findings but you can find the full paper here if you’d like to read further.

BEE HOTELS

Solitary bees, unlike the familiar honeybees, don’t live in social groups. They often nest in either holes in the ground, crevices in the mortar of brick walls or hollow plant stems. The concept of bee hotels is to replicate these niches and provide a habitat to raise their young. However, often these bee hotels aren’t made to their required specifications; many are produced abroad and so the hole sizes aren’t suitable for our native bees, some don’t have a back and act as a wind tunnel, and the length of the tubes aren’t always appropriate. Research has shown that for the species Osmia bicornis when the tube lengths are less than 130mm there is a sex ratio shift towards male bees, and that 150mm tubes are the optimal length.

Mining bee, Andrena sp.

Another issue is that bees wouldn’t naturally congregate in the same densities that can be found in bee hotels – especially the larger ones. Solitary bees can be predated on by parasitic wasps which you may sometimes see scanning the side of your house searching for a masonry bee nest. Bee hotels offer easy pickings for these wasps as once they have found one nest they can go on to predate on the ones near by too – potentially having quite a detrimental impact on the local population of the bees using the bee hotels.

Ruby-tailed wasp, Chrysis sp. is a cuckoo wasp which lays it’s eggs in the nests of mason bees. The young emerge and consume the hosts eggs and young.

Bee bricks which are marketed as being a permanent solution to be added to buildings and developments were also considered in the report and the general consensus was that whilst they aren’t great for bees, they make great (expensive) spider habitats!

An elaborate bee hotel at the Hampton Court Flower Show 2015.

SEED BALLS

So what about seed balls? These can be bought online and aren’t particularly cheap – you can get many more seeds for your money buy buying seed packets. However, the fancy tin and novel idea of throwing the seed balls around definitely has an appeal. But do they work? My daughter was bought some one year, and we found they didn’t’ germinate at all, and the reviews online used in the report suggest the same.

Rusty Berlew, described as a ‘master beekeper’ explains how the sites where the balls are thrown often aren’t suitable for the seeds. When I looked at the ‘Bee Mix’ it lists some of the species which include ‘Birdsfoot Trefoil, Foxglove, Red Clover, Viper’s Bugloss and Wild Marjoram’ – but I know from experience germinating these species from seed in a greenhouse, that viper’s bugloss requires very different conditions to foxgloves, marjoram and clover and birdsfoot trefoil. Foxgloves are woodland plants whereas the others are more suited to meadows and open grassland. So whilst yes, they are all good plants for bees, they all require quite different conditions to thrive.

Bees love foxgloves
Viper’s bugloss on Hove beach. Quite a different habitat to that of a foxglove.

In all, the report really highlights that there is much more research needed to show if any of these products are beneficial to wildlife, or certainly to measure the negative impact they may potentially have on populations.

In the meantime, if you want to help wildlife, you’d be better off buying a bag of seeds suited to your garden, leaving dead plants and leaves over winter and providing log piles – and they’re all much better for your pocket too!