Deciding the subject of my dissertation turned out to be relatively simple, although with so many interesting topics to study, it was hard to choose. I wanted to study something at an interesting location to produce findings that could have a practical conservation application. Reading ‘A Sting in the Tale’ by Dave Goulson proved to be influential on my decision to study bees: it’s full of fascinating information about the ecology and behaviour of bumblebees. There are over 270 species of bee across the UK and there is still much to learn about their abundance and distribution.
After reading so much about bees, I started to notice them much more, especially the really small ones that previously I would have thought were small flies. Solitary bees can be as tiny as 3.5mm, (e.g. some Hylaeus species). The range of sizes of bees of the same species can vary: the smallest workers of Buff-tailed bumblebees (Bombus terrestris) can be 11mm, whilst the largest queens can reach 22mm. Worker’s body masses can vary up to ten times between individuals: this is called size polymorphism.
One of my favourite places to visit is Charnwood Lodge in northwest Leicestershire: a ‘wild’ expanse of heath, woodland and grassland with a profusion of interesting species present, including green hairstreak butterflies and willow warblers. When visiting last spring, I noticed that much of the wildlife I encountered was centred on the patches of gorse scrub scattered across the site: ladybirds, spiders, green hairstreaks and bees. Having volunteered with the Wildlife Trust in this area a few times before, I knew that ‘scrub bashing’ was a key part of habitat management on the acid and heath grasslands. I felt compelled to find out more about the scrub on the reserve after I had been a participant in the contradictory actions of marvelling at and destroying the scrub.
I was surprised to learn that scrub wasn’t listed as a priority habitat in the Leicestershire and Rutland Biodiversity Action Plan. Although often lumped together with woodland, scrub is an important habitat in its own right, providing food for many invertebrates, shelter for reptiles and nesting opportunities for many species of birds. As part of my study, I wanted to discover which characteristics of scrub provided the most benefit for foraging bees. I surveyed bees on transects of bramble and gorse across nature reserves in the Charnwood forest throughout spring and summer. The scrub characteristics included: size of scrub patch, growth structure, amount of shade, aspect and level of connectivity.
Throughout the course of the study, my discoveries about bees and pollination grew and grew. I never knew that bees actually have five eyes; the additional three are called ocelli and are located on the top of the head. These simple eyes detect changes in light and movement, whilst the two more complex compound eyes perceive a range of colours, including ultraviolet.
I was aware of the threats bees face from a multitude of factors including habitat loss and pesticides, but their habitat requirements are complex, with suitable nesting sites and sufficient food resources essential for survival. One bee can visit up to 6,000 flowers in one day: the presence of an abundance of flowers throughout the growing season is extremely important. A bee’s full stomach will only last around forty minutes. Studies have found that bumblebee colonies will grow faster and support more individuals when their nest is near to extensive patches of flowers. Some species have declined drastically due to the absence of sufficient floral resources: the great yellow bumblebee (Bombus distinguendus) used to be widespread in the UK, but is now restricted to northwest Scotland where traditional crofting practices allow wildflowers such as clovers to persist in sufficient numbers.
Flowers in the Legume family (e.g. clovers) are preferred as the protein content of the pollen is around 35%, higher than other plants. Pollen is fed to developing bee larvae and is more nutritious when bees are situated in more natural landscapes.
The life-cycles of solitary and social bees differ, with different species occupying specific niches, be it tree or subterranean nesting habits or emerging early or late in the year. Both groups of bees have an annual life-cycle, occasionally producing two generations in a year. Bumblebee queens are the only bee of the colony to survive the winter, with the workers and males dying off after all the males and queens have been produced. This queen will found the nest, collecting pollen in which to lay the eggs and will then rear her first brood. Once these bees (all female) have emerged from pupation, they will take charge of rearing each batch of larvae: firstly their sisters and later, their brothers.
Solitary bees have no queen or colony, with individual female bees laying single eggs in chambers of cavities in stems or in underground burrows. Some species make use of leaves and mud to create nest cells and others are cuckoo species, laying their own eggs in other bee’s nest cells. Although they are laid last, the males hatch first. After growing by feeding on a ball of pollen provided in each chamber, the young bees overwinter as pupae before emerging in spring.
There is still much to learn about the foraging range of the majority of bee species. Buff tailed bumblebees are able to fly over 5km and honeybees up to 6km, with the ability to fly directly to flowers from the nest. Smaller solitary bees have been recorded flying between 150 and 600m: this knowledge is vitally important if we are to conserve bees at a landscape scale by ensuring nesting and foraging habitats are close to each other.
It is truly amazing how large bumblebee queens can fly in temperatures lower than 4°C, considering they require their flight muscles to exceed 30°C. Smaller bees cannot fly in such cold conditions, becoming active over 10°C. Thermoregulation is achieved by shivering the flight muscles and enabled by fructose bisphosphatase enzymes. Some bee species (such as red tailed bumblebees) have higher levels of this enzyme, meaning they can forage on large patches of flowers for longer.
My study found that scrub was an important floral resource for bees throughout spring and summer. The results showed that foraging bee species richness and abundance was significantly higher on scrub patches that were light, south-facing and with a compact growth structure. South-facing scrub patches in full sun were most important in spring, when their warmer microclimates were vital to allow bees to maintain a suitable temperature to fly and forage efficiently. When spring weather is poor, the difference of a slight increase in temperature can improve the chances of a foraging bee. Scrub with a compact growth structure appeared to have more inflorescences than older, leggy scrub. With an increase in flowers, there will be an increase in bee abundance, with longer foraging times on flowers. Although studies have found that pollinators will show preference for larger flower patches, the size of the scrub patches wasn’t an influential factor on bee abundance in the study.
The ideal conditions can be created for bees and other pollinators through sensitive scrub management. The current programme of grazing with English Longhorn cattle helps to keep the heath-grassland areas open by preventing the establishment of scrub seedlings, allowing the grassland flowers to thrive. Established blocks of scrub can be cleared to created sheltered, south-facing bays, with as much boundary:area ratio as possible. To encourage a wide age-range of scrub, rotational cutting can be carried out, similar to managing a coppice woodland.
I reached the aims I have set out to achieve: my study was successful in providing an insight into the scrub characteristics beneficial for foraging bees and my results will have a practical application by informing the scrub management programmes across the reserves. I was also pleased to generate new records for the Wildlife Trust across the study sites, recording 19 species of bee in total.
Thanks go to Senior Conservation Officer Neil Pilcher and my tutor James Littlemore for their advice and support throughout the study.
References – Bumblebees: Behaviour, Ecology, and Conservation by Dave Goulson and Field Guide to the Bees of Great Britain and Ireland by Steven Falk