Leafcutter bees, rarely seen by many people but ever so useful!

Probably patchwork leafcutter bee damage to rose leaf

I designed my award-winning solitary bee nest box for numerous reasons. I found the other commercial ones turned out to be’ bee cemeteries ‘ not bee hotels, for the leaf cutters and red mason bees and my family and I had difficulty viewing what was going on.  Now everybody can view what is going on inside the cavities and even the cells with red mason bees! See six different species including Leafcutters in the video and one cuckoo bee, with interesting facts below. You may be interested in a newly updated article, “Beware! Is your ‘bee hotel’ a nursery for disease and pests?

See my new leafcutter bee attractant spray

Pollinators of our food under threat

We have all heard of honey bees, living in large numbers in their hives, bumblebees living in much smaller colonies but many people have not heard of or are aware of another group of important pollinators of our food, in particular fruits and flowers. That group is the harmless solitary bees, which themselves comprise of 3 main groups of which there are around 250 species: miners, leaf cutters and mason bees. Like bumblebees, these essential pollinators are under threat from the destruction of their habitats, pesticides and lack of forage. We were becoming increasingly dependent upon one species of pollinator, the honey bee, possibly because we also gained honey and other hive products from it as well as some crops from its pollination services. The difficulties that honey bees are currently going through should start to raise alarms. We just cannot rely upon one species alone to pollinate our food. We should begin to help the other, less well known wild species in our quest for pollination and hence food supply and food security.

Where will they nest?

Leaf cutter bee larva in cell Nurturing Nature

This photograph was taken from one of my solitary bee nest boxes and is a larva inside its leaf cell. Next door to it in the next cell was a leafcutter assassin with video

An enormous diversity of leafcutter bees (Megachile spp.)) are ground-nesters, as are a good number of Osmia bees.  For both, the nests are typically short, shallow, and sometimes branched. (pers. comm. JH).  Miner bees can construct their cavities in sandy/loamy soil. Usually, leaf cutters like mason bees, like to nest in a readily made cavity. They use hollow stems, holes in walls, fence post holes and other similar cavities, providing the width was to their liking. Leafcutter bees will also nest inside containers, such a hanging baskets and plant pots, esp. M. willughbiella. I suspect that the compost is something they can easily manage as they force their way through to make cavities. The leaf cells will contain a mixture of nectar and pollen and are very fluid as you can see above. They have to be waterproof, or the liquid food would simply ooze out of the cell.

We can help them by providing cavities to nest in, and there are many solitary bees nest boxes available to buy at garden centres. Personally, I like watching these fascinating bees and have bought nest boxes, one almost 20 years old, that allows you to observe them up close, without too much disturbance to the bees. However, at the time they were probably the best available for bee observation. They do have significant drawbacks.

 

Solitary bee nest tubes with mould Nurturing Nature

Moisture cannot wick away causing a fungal infection of the pollen, and the bee larva dies. Raw states ” Glass tubes are undesirable because condensation on the inside of the tube killed the occupants.”

Drawbacks

Being completely circular and acrylic any moisture that enters on the bee or pollen wicks into the surrounding material, which in this case is the pollen. It carries a risk of fungal infection of the larval food, and thus its death, especially with Red Mason bees. The acrylic tube restricts the airflow and retains moisture. I have lost many Red Mason bees because of this. Yes, they are excellent for observations and have been in use for years. But later in the year, I did find that most of the bees were dead, killed by the dampness and mould that grew in the tubes as you can see above. I want to observe bees and their parasites. I want to increase bees numbers, not kill them! I would not use them now. The smaller the tube, the greater the infection risk and I found the same thing happened to solitary, predatory wasps.  The tubes are a real pain to clean for adults and children. They made management of the bees difficult. Hence my design of nest box which I now sell! They have been a tremendous success and more importantly a success for solitary bees!

 

Nurturing Nature solitary bee nest box

Observe with ease what is going on inside the cavities

The two most common species of leafcutter bees in the UK probably are, Megachile centuncularis (Patchwork leafcutter) and M. willughbiella. Besides leafcutter bees, mason bees and some small predatory solitary wasps  (with the optional extra nesting blocks) have all used the nest boxes.  The predatory wasps store living but paralysed sawflies, aphids and caterpillars inside the cavities, then lay an egg with a hearty feast awaiting the young wasp grub! The different species of solitary bees and small predatory wasps, simply do not bother with each other, all intent on supplying for their offspring only and concentrate on completing their tasks within their cavity, each of which is in effect, the nest. So you can watch a wasp stockpile the caterpillars etc., in one cavity for its young with a mason bee or leafcutter bee in the next cavity! Each separate hole is, in fact, a nest site for the particular bee or wasp species, using it. Once full, generally the females will go off in search of another nesting site, which very often is the same nest box, space allowing.

 

Mason and leafcutter bees can easily be observed in the transparent tubes but may die later in the year

The white polystyrene at the ends of the tubes is to stop spiders, earwigs and any other undesirable pests from entering. If a bee finds a spider inside an possible nest site, she obviously will not use it or worse she could fall victim to it if it has the web. Spiders will occupy cavities as a shelter, probably before deciding to make the web inside the cavity. Earwigs will shelter inside them and eat the pollen and stores of food intended for the bees.

 

A wooden nesting box for solitary bees- N.B., Mud sealed cell on the left. But how old is it?

Another commercially available solitary bee nesting box. This one has at least one cell fully occupied and sealed by mud, a trademark of a mason bee. Leafcutters in my garden, rarely use this type of box at all, only the red mason bees. Why is this? My research has found that without proper management, (details come with my instructions) these type of nest boxes, can also be a death trap for bees, over time when a disease can spread from the cavity or pollen mites take over each nest cavity leading to bee larvae demise or death. Drilled wooden blocks, a simple DIY attempt, is now old technology and again allows for the increase of pests and diseases inside each hole. Management of these is impossible. Bamboo tubes are cheap and cheerful, but make management difficult. Management of bees can significantly enhance the bee population.

Their life begins.

After emerging from her cocoon in which she overwintered, possibly late May or June in my garden, the female leafcutters bees feed themselves up with nectar for energy and pollen in readiness for egg laying, find a mate and then go in search of a suitably sized cavity. Depth, diameter and material will influence her choice. After selecting one, she will, like bumblebees, undertake a zig-zag orientation flight in which she is in effect, making a mental note of the entrance hole and its location memorising its exact location. Once found, if it was previously used by another bee, she will clean out the debris before the cell construction process begins.

Leaf cutter bee lines the cavity with leaves Nurturing Nature

 

Nest building

See my video of them nest building. using pieces of cut leaf, hence their name.

See a video of a leafcutter bee using pink rose petals to make her nest, which is a first for me. She wanted a little colour!

The whole process of nest making can take some time. They only live for a few weeks so time is of the essence. Inclement weather stops them. They have only one brood a year and never see their offspring.  Time is very important to them. After mating and feeding up, she has to find a suitable cavity. Leafcutter bees select a suitably soft rose leaf, lilac, beech or willow herb leaf, starting from the outer edge and using their jaws, (mandibles) cut a semi-circular shape around the outer edge. As the leaf is about to drop she resumes flying and carries the leaf underneath her body, using her all of her front legs, tucked under her abdomen and jaws, to make it as aerodynamic as possible to give the least resistance and drag against the airflow. Ospreys carry a fish it has just caught, with the narrowest edges facing the way it is flying. She uses these pieces to line the outer walls of the cavity, making a hollow cigar shape. She uses different disc-shaped pieces of leaf to cap an individual cell within the cigar-shaped tube.

Provisioning

Then she stocks the cell with pollen and nectar using much more nectar than the red mason bee, tamps down the food with her abdomen, lays an egg on top of the food mound, then closes that cell using the disc-shaped pieces of leaf sealing it with a leaf/saliva mixture and starts again with the next cell. As each particular cell can take nearly 10 hours to build and provision, with an average 21 trips to construct the cell and 18 trips to provision the cell with pollen/nectar, the process can take a few weeks, particularly if the weather is bad. In essence, her life is based around a complex sequence of stereotyped behaviour: nest searching ➞ nest inspection ➞ leaf gathering ➞ pollen/nectar gathering ➞ egg laying ➞ leaf gathering ➞ leaf sealing and so on until that particular cavity is filled. She may lay 30-50 eggs if she is lucky, depending upon her finding enough cavities to fill.

 

Leafcutter bee cutting a leaf used as nest lining material

 

I would imagine that carrying the leaf must be rather tiring for the female leafcutter as the leaf can weigh a 1/4 of her weight! Recently at Speke Hall in Speke, Liverpool, I saw this female having a breather, rather appropriately on a wooden table with two benches, one of those that we use to have a rest ourselves! There was another leaf cutter actually inspecting old nail holes in the very same bench!

 

Female cutter bee with her nest lining material, having a rest at Speke Hall, Liverpool!

 

I have often seen them inside their cells on cold, wet or windy days, sitting there, with their heads just near the cell entrance, awaiting better weather. As it is the actual provision of food for the cells takes most of the time, it would help if we could provide suitable flowers nearby, (as unlike honey or bumblebees, solitary bees do not forage over great distances), for them to forage on. (List with my instructions!)  Whilst awaiting better weather, I have seen them, particularly during the inclement daytime weather and early evenings, prepared to defend their eggs, waiting near the entrance with their jaws open ready to repel predators. Unfortunately, when they are out foraging for food and provisions the cells are left undefended. This leaves ample time for a host of predators and parasites to enter the cells and lay their own eggs…..  a topic in its own right!

 

Leafcutter bee cells with an opportunistic mason bee in the last cell

 

Above you can see 3-4 leafcutter “cigars”! each containing provisions, lined with cut leaves and sealed with a leaf pulp. However, this female may have died as she never constructed the very last feel. This was made by an opportunistic mason bee, which you can see is totally different. She has sealed the right od her cell with mud, provisioned it with pollen upon which she has laid her egg and sealed the entrance to the whole tube with mud. Would the leafcutter bees be able to cut their way out through the mud wall with their leaf cutting mandibles?

Yes, you can view what is going on, BUT there is no oxygen exchange and no escape for moisture. I have found scores of dead bees over the years inside the tubes over the autumn and winter months. They are a devil to clean and remove viable cocoons. I needed a much easier option and one which did not kill the bees.

 

Leafcutter bee cell ( cigar!) with a young bee inside shortly to emerge

leafcutter bee cell to the right and mason bee cocoon on left

Both of the above cells were lucky. They were overwintered, away from predators. Unfortunately, the one below was taken by a bird, possibly a woodpecker that visits the garden looking at the damage to the front wooden cover. This certainly is a case of last in, first out!

 

Great tit damage to nest cavity entrance

A few little soil mounds in your lawn may well be a female mining bee or even a solitary wasp excavating a tunnel for her young. A few little chunks out of your prized roses will likely be the leafcutter bee, the bee hovering around a few holes in your wall could well be the mason bees. So next time you are enjoying your chilled glass of cider, or crunching into a juicy apple, highly likely that the apples used were pollinated by one species of bee or another. Cheers!

Have a look at the 11 species of bee, including several different species of leafcutter bee, that have used my award-winning solitary bee observation nest box.

“All my articles and videos, available free, are funded by my teaching, presentations, sales of award-winning bumblebee nest boxessolitary bee boxes, and wormeries. Please help by spreading the word and forwarding this link to your friends and colleagues. https://nurturing-nature.co.uk  Thank you” George Pilkington MSc Cert. Ed

For more information about solitary bees and wasps visit BWARS

For more bumblebee information and to help save bumblebees join the Bumblebee Conservation Trust at Stirling University

For a MS word doc info sheet about the three most commonly seen in gardens leafcutters bees from the Natural History Museum, download here (although the link states Garden Spider!)

Refs: Besides my own experiences and observations…..

Anon, (2009), ” Solitary Bees”, International Bee Research Association”, Cardiff

Mader, E et al (2010)” Managing alternative pollinators”, Natural Resource, Agriculture and Engineering Service, New York

O’Toole, C, (2000), “The red mason bee, taking the sting out of bee keeping”, Osmia publication, Banbury

Pers. comm JH James H. Cane , USDA-ARS Pollinating Insect Research Unit Utah State University, Logan.

Raw, A (1998) “Nesting biology of the leaf-cutter bee Megachile centuncularis (L.) (Hymenoptera: Megachilidae) in Britain”.
ENTOMOLOGIST. Vol. 107, no. 1, pp. 52-56. 1988.

Raw, A (1972) “The biology of the solitary bee Osmia rufa”, Trans. R. ent. Soc. Lond. 124 (3), pp. 213-229, I fig.  1972

 

Thanks for photo of damaged rose from Neil Bromhall an interesting web site….  www.rightplants4me.co.uk