Beware! Is your ‘bee hotel’ a nursery for disease and pests?

Or put another way, why does n’t my bee hotel work and increase my wild bees? I wish, from my experience as a researcher, educator, designer, user and producer of bee boxes, to shed light on the controversy over the effectiveness or otherwise of bee hotels. The controversy is to do with the design, construction and maintenance of bee hotels and in particular, the nest cavities that, it can be argued, have a  significant influence on the survival outcomes for bees. Researchers have just published what I have found myself, that bee hotels are not what they appear!

From a customer AM, who bought a bee hotel from another supplier;

‘Did what you said had a look at the bees and sadly they were all dead having been eaten by tiny grubs, how can I be sure this doesn’t happen again. I am really upset., as I looked after them all winter keeping under a porch out of all weathers’.

In their paper ‘Bee Hotels’ as Tools For Native Pollinator Conservation: A Premature Verdict? they found ” at their worst, bee hotels may act as a population sink for bees through facilitating the increase of parasites, predators….and diseases”

A positive experience

You could call me biased as I build and sell award-winning bumblebee and solitary bee observational nest boxes because I wanted to encourage a wider scientific study, education and enhance public awareness with a positive experience from seeing the different bees and solitary wasps that use them. Many people are simply not aware of solitary bees or solitary wasps, hence I have spent a very long time writing and updating a comprehensive set of instructions for my customers. Nevertheless, from both my experiences over the years and that of other researchers, there is substantial evidence that different bee hotels are more effective than others. Some designs just don’t work, have harmful or minimal outputs for bees in terms of survival from predators, disease and environmental factors.

Successful or otherwise?

To me, success is not if the solitary bees use the nest box. Highly like some will. It is a success if a new generation of healthy solitary bees emerges from it the following year and better still in more numbers.

Red mason male feeding

Management and design is key

I believe the key considerations when considering the effectiveness of bee hotels is the ease of management along with how it is designed. Annual and informed management is essential to improve the positive outcomes for bees. Just as you manage the countryside and urban green spaces and in particular nature reserves to improve the outcomes for birds, mammals and plants there is a need to manage insects, including bees for a positive outcome. Some of us wish to do the same with our gardens. Unmanaged bee hotels of certain designs and materials may have their place but the evidence is increasing that the positive outcomes for bees can be minimal or even negative. I invite you to consider my discussion below to enlighten you about the controversy over bee hotels and make up your own mind.

This is my two penneth!!

I have made some videos and given a few explanations as to my experiences as to why many bee hotels can actually kill bees in my garden. I show several other methods for attracting wild bees/wasps and thoughts you may wish to consider before placing them out. I regard myself as a wild beekeeper, especially red mason and leafcutter bees and as such, like a honey beekeeper, I want to manage my garden bees and protect them from pests, predators and the like. A few species of solitary wasps have used my nest boxes. Different pests I have come across, require different control measures, which can also depend upon the nest material in use. My advice would be, if you can’t open it to clean it out, don’t buy it! With homemade/collected materials at the very least, they should be changed annually.

Bee hotels?

A slick marketing and snappy name for people to remember! There is a huge choice of designs, materials etc., out there nowadays, some look really good and pleasing to the eye! Firstly they are not bee hotels! Other insects may use them as an ‘insect hotel’ for temporary resting, shelter or feeding places. The solitary bees, e.g. red mason bees, live as cocoons inside the cavities from late spring to the next spring. Other bees do likewise from summer to summer as do some solitary wasps. Hardly a hotel, more a bee home!

What will use them?

It’s not like a bird’s nest box when you can say in the main, which birds will use it. Other than a few bees and solitary wasps that I do know, which other bees or solitary wasps will use them I have no idea. It is a question most people in the UK cannot answer. Other than a book about solitary wasps Prof. Sarah Corbet, there a very few solitary bee/wasps academics here and finding a book on the subject is frustrating! Though I can fully appreciate the time, effort and expertise needed to write one! There are a couple of interesting books on solitary bees that I would recommend by Steven Falk and Ted Benton. A useful website to visit for photographs and information is BWARS.  Then you see one that looks like it to discover there’s another that looks exactly the same!! At least its a start!

Is your ‘bee hotel’ a nursery for disease and pests?

There may well be many unwelcome guests, all after the rich pollen/nectar mix or even the bee egg, larvae or cocoons themselves.

Pollen Mites (Chaetodactylus spp.)

Pollen mite claws Nurturing Nature

Pollen mites attach themselves to bees using huge claws, (above) attach themselves to bees inside their natal cavity, hitch a lift and return to a nest site where they alight. Once inside the safe environment of a red mason bee’s cell, they breed and can soon become many thousands inside one cell, outcompeting the bee larvae for food, leading to its death or reduce the size of the bee. Smaller female bees have reduced fecundity. For the bee larvae, it is a race against time.  According to some researchers, they may also eat the egg before it hatches and even certain later stages of larval development.

a new film with new research

To cater to environmental factors within the cell, probably food scarcity or decreasing humidity, they have developed a survival strategy. Some become migratory mites and migrate as described, waiting till spring when the bee leaves its cell or as it passes through a mite infested cell, often found in huge numbers that it can affect the flight of the bee.

Encysted pollen mite bidding their time inside a Red Mason bee nest

The above mites probably moved out of the natal cell as there is evidence of Cacoxenus indagator frass which means they may have eaten most of the pollen which forced the mites to leave and encyst becoming non-migratory

They can remain in situ inside your solitary bee nest until some environmental cue triggers their activity. It’s a survival strategy that works as they can remain dormant during unfavourable conditions for several years. Your bee nest may well now contain many 1000’s. These methods enable them to maintain their normal host relationship and disperse to gain new hosts.

Nest to nest dispersal

Other than those that hitch a lift (phoresy) on a bee, mites will also disperse within solitary bee nests by walking to nearby nest entrance holes, walking from nest to nest through splits, cracks, holes, gaps, and parasitic wasp emergence holes, all of which can be found in wood, straws, canes, reeds, paper/cardboard tubes.

Wasps and other pests

In my garden, parasitoid wasps, such as Monodontomerus wasps can devastate red mason cocoons, likewise Pteromalus wasps with leafcutter bees. Artificially large numbers of solitary bees will produce a huge amount of frass. Parasitoid wasps, in particular, seek out and can recognise their host’s frass, which gives off chemical cues. Manage these to stop them from eating your bees! For me, that’s essential. I do find these wasps fascinating and they are part of the whole web of life.

Other pests will seek out pollen stores/larvae/cocoons all concentrated in one easy to find location. Many of these pests may otherwise be scarce in wild populations.

Wasps such as ruby tailed, Sapyga quinquepunctata and the cuckoo bee Coelioxys spp. are minor cleptoparasitic pests in comparison to the parasitoid wasps, as is the Houdini fly, Cacoxenus indagator. in my garden currently. This may change as these things do in nature!

Chalkbrood

A fungal disease caused by Ascosphaera spp. (not the honey bee species) infects the bee larvae and kills them. It is scarce in wild populations. Under managed and high densities of bee populations, it has the ability to rapidly spread. Its spores have been found to live for many years. The spread of this disease has to be prevented. Your old solitary bee nest may be a source.

If a diseased infected bee larva dies in its brood cell, the bees further inside the cavity will have to chew through its body as they exit. If they don’t they will die inside. The spores can be picked up by all exit-ing adult bees in that cavity. This does not kill the adult bees themselves, but certainly, the spores will spread to flowers they visit and passed onto other bees visiting them. Their own offspring may themselves be infected as spores drop from the adult bee to infect the pollen that is consumed by the larvae. Once ingested the larva will die.

Transparent tubes

 

Solitary bee nest tubes with mould Nurturing Nature

Moisture cannot wick away causing fungal infection of the pollen and the bee larvae die. Raw states “Glass tubes have been found undesirable, because condensation on the inside of the tube killed the occupants”

The tubes are a real pain to clean for adults and children. They made the management of the bees very difficult. I want to observe bees and their parasites. I want to increase bee numbers, not kill them!

Cheap, cheerful but a false logic?

Well intentioned but woefully inadequate

Spits & cracks in bee hotels allow pests to enter-Nurturing Nature

Drilled wooden blocks, a simple to make the DIY attempt, is now old technology and again allows for the increase of pests and diseases inside each hole.  Management of them is impossible. 

How many pests are inside this bee hotel?

Upon first impressions, the above drilled log appears to be a great success with high occupancy. It probably is, for pests!! The splits make it very easy for pests to migrate from one cell to the next and easy for solitary wasps to parasitise the cocoons. Inserting paper rolls inside is fiddly and any gaps can allow wasps to enter, but can help with pollen mites. They have to be a tight fit and be able to be pulled out. They are liable to get wet in the rain without adequate shelter. It may be a good idea to replace wooden blocks, logs, annually to help prevent pest/disease build up.

 

Wide windy tunnels - Nurturing Nature

Wide windy opened ended tunnels are not liked by solitary bees!

Not a very bee friendly bamboo bee hotel! Nurturing Nature

Bamboo tubes are tough, waterproof, cheap and cheerful and should be changed annualy. They are easily replaced and with experience, time spent cutting, sorting re lengths, width etc., can be made to work very well and allows for management of bee cocoons. Inserting paper rolls inside is fiddly and any gaps can allow wasps to enter, bamboo diameters can be variable. Many shop bought ones have nodes halfway down making them smaller or even blocked by a node at the entrance!  Many of these are simply too wide and again act like wind tunnels. The brittle sharp edges have not been clean cut and are not very friendly to bee wings! Any cracks or splits would be exploited by parasitic wasps.

Opening bamboo canes to check for bee cocoons

I was asked to advise about red mason bees and offered to examine their old bamboo bee nest, which had been put up for years to encourage  red mason bees to use in their showcase orchard, as part of a well known and beautiful garden in the North West. It had not been managed. It may have been put out for the bees but had it been used and what was the result?

Inspecting bamboo canes for bee cocoons Nurturing Nature

The canes were split open to allow us to see what was inside and more importantly, how many red mason bees cocoons there were to pollinate the apples.

Bee cocoons from an old bamboo bee nest box Nurturing Nature

Out of all those canes we were left with just a few cocoons, which MAY have been viable ones! Bamboo canes need replacing annually.

Mono exit holes in canes

Even phragmites canes can be attacked by Monodontomerus wasps…..and allow pollen mites to enter

Reed, plant stems, cardboard tubes and straws

High hole densities allows pest, diseases to spread _ Nurturing Nature

High holed densities may favour the spread of diseases, pests, mites. The different shapes, lengths, positions make it easier for solitary bees/wasps to find their own actual nest. Would need replacing annually. Can be very successful. In the distant past  I used hogweed stems, but got no takers. So I don’t bother now!

Canes destroyed by birds

Reed and plant stems can be very effective for solitary bees and wasps, but open to attack by Monodontomerus wasps and without protection, birds and mice. Wood makes an excellent container to house bamboo, reeds, etc. Metal is may not be a good idea, as it can heat up in the hot sun. The bee larvae may overheat,  the nectar may dry up and worst the bees are cooked! Unless of course you put a shelter roof over it or remove it before it gets too hot.

Cardboard tubes

They have to be thick enough to stop monodontomerus wasps ovispositing through them and having a sealed back end is required. They need to be protected from the rain and are best kept inside a waterproof container with an overhanging roof, or the protruding end gets wet. They work admirably but can start to become expensive. Some people put a paper liner inside to help make cleaning them easier. I don’t use these anymore.

Grooved boards as bee nests

old and new grooved boarded bee nest Nurturing Nature

These work but need cleaning and managed. You cannot see what is going on and have to unscrew them disturbing the fragile bee larvae if you want to watch them. They were put up next to one another in the same year. The old one I had not used for a few years. It had not therefore been cleaned and I left it like that to see how it performed. The other one on the left was brand new. You can see the bees preferred the new unused one to the old one.

Birds and mice

The British green wood pecker has a 10cm long tongue which is so long it has to be wrapped inside its skull and the greater spotted woodpeckers tongue can extend 4cm out of its mouth. A mesh in front of the nest box is hardly a deterrent with a long barbed tongue. Great tits also relish bee cocoons, as do mice when bee cocoons are left in situ inside reeds or bamboo canes or stored without adequate protection. Managing against such predators will increase your solitary bees. The nest blocks I use you simply turn the whole nesting unit around so they now face the inner wall!

Wrong positioning 

Several negative aspects affect the nest box position. If you position the nest box in the wrong place, I have found pests such as ants and earwigs soon find them, both of which can eat the pollen and eggs. Spiders can also take up residence! Weather, wind, rain, shelter, damp and vegetation can all have negative effects.

How positioned

The way and means the nest box is affixed to its permanent place can have negative effects on the bee boxes and consequently the bees.

Cavities

Solitary bees and solitary wasps build cells inside cavities. The length, width and materials used all have a bearing on the success or otherwise for the occupants.

Bigger is not always best.

I would recommend that you do not build large solitary bee nests, albeit some look fantastic! A high concentrations of bees is more likely to attract pests and predators and makes it more easy for disease to quickly spread. Instead have many smaller nest boxes to spread the risk.

Safe inside a Nurturing Nature nest block

This is what I designed to help eliminate many of the above problems with management.

Wild Bee Box with easy interchangeable nest blocks for other species

Wild Bee Box with easy adaptable nest blocks for other species

Why use Wooden Nesting Blocks by Nurturing Nature?

Many Solitary bees prefer to use wood to nest in

Easily cleaned and removed from nest box casing

Nest box casing design and dead end cavities allows for additional materials to be added to minimise parasitoid wasps

Easily viewed for inspection and pest/debris removal

Absorbs excess moisture by wicking it away from moist pollen reducing the likelihood of mould formation which destroys cells

Long term investment, natural resource, reuse many times over

Harvesting of cocoons simplified (kids love this aspect!)

With management has the potential to increase your red mason bee pollinators

The dead-end cavities are easily adapted to cater for different solitary bees and harmless solitary wasps

The cavities are designed to save the bees time and encourage more females

Allows ‘loose cell’ or closed ‘cell management’

Widely spaced holes avoids high hole density nest finding confusion

24 reusable cavities for bees, 6 holes per nest block x 4 per nest box

Full detailed instructions and personal after care service.