How to Help Native Bees

Honey Bees are Not the Only Bee Species

In the public eye, “Save the Bees” doesn’t capture the variety of bee species beyond the honey and bumble bees, and so this article examines what can be done to help these native, wild bees. In most species, these bees nest individually; only a small number of social species form (large) colonies. To define native bees is to define their geography: many are naturally found within a specific region and ecological niche, as opposed to our humble honey bee Apis mellifera, which has spread into the world from Asia.

There are over 20,000 named species of native bees, each with their own behaviours and features. Within their niche, they pollinate wild plants and maintain biodiversity. These native species are often more efficient than honey bees in crop pollination due to their flower specificity, however due to their solitary nature, they are harder to use in commercial pollination operations.

This examines what beekeepers and environmental enthusiasts can do to promote native bee habitats who face habitat loss, competition honey bees, pesticides, invasive plants & climate change et al.,. Native bees are often limited by the absence of their natural nesting sites (“non-flora resources”; reviewed in Requier & Leonhardt, 2019) rather than their host plants, and fortunately, it is easier (and quicker!) to construct these habitats while simultaneously maintaining a flowering garden.

There are two shirts that go with this article, designed & printed by yours truly:

Helping Native Bees: Ground Nesting Bees

Native bees that nest in the soil represent the majority of the species and are dominant in open habitats; carving burrows in areas where other solitary bees live. This proximity to other bees is an indicator that the general region is suitable for rearing brood, which prompts the females to commence nest building. The families Andrenidae (mining bees) and Melittidae (a small bee family mainly found in Africa) are ground-nesting, as are most species of Halictidae (sweat bees) and Colletidae (plasterer bees). For further reading, the excellent book “Bees of the World” by Charles Michner is recommended.

In Germany, a 2022 study by Neumuller & colleagues attempted to increase native bee biodiversity by artificially constructing hills from the local¹ soil across 20 regions with the country. After two years of monitoring, their artificial nesting sites housed 119 species of wild, solitary bees, with 37 of them belonging in the “threatened or rare” species list. The second year saw a greater population compared to the first, as the first bees began the colonization process, and subsequent generations expanded upon it. The success of the nesting hills in attracting bees from various habitats is attributed to their structure, which consisted of semi-natural grasslands, flower plantings, and residual (i.e. previous-year) habitats.

Native Bees in Commercial Pollination Settings

While not as reliable as honey bees in large scale pollinations, ground nesting bees from the Andrenid family have been studied in apple orchard pollination within the United Kingdom (Fountain et al., 2023). Many species are more effective than honey bees in the transfer of pollen between flowers, which increases the rate of successful fertilization as these larger-sized bees carry pollen more effectively (Garratt et al., 2016).

In the apple orchards, a total of 58 wild bee species were identified over a three-year period, with activity peaking alongside that of the blossoms, declining as the flowers dwindle. The results showed that bees preferred to nest in bare soil created by herbicide use (Glyphosate for those curious), with species more involved in the pollination selecting bare patches closer to trees. This nesting preference is likely due to the absence of roots and other plant matter, which can make burrowing and excavations more difficult.

From this study, the authors conclude that promoting vegetation-free, bare-ground habitats during peak nesting times increases the chances of successful apple pollination. In large orchards, these soil patches should be placed near or directly underneath the trees, as solitary bees do not forage far from their nests. Some smaller species from the family Apidae forage up to 300 meters away from their nest in the ground while others much less; diminutive distances compared to the 10 kilometer radius of honey bees (Wright et al., 2015).

Helping Native Bees: Hollow Plant Stems, Cavity & Crevice Nesters

Enter the Bee Hotel: A solitary bee nest purchasable from many stores and created for the above-ground nesting bees. Most native bees that nest in hollow stems and cavities are dominated by the families of Megachildae (leafcutter bees) and Apidae (containing the common bees we know and love: honey-, bumble-, carpenter bees, and more!). Disclaimer: these hotels one “tool” in the helping native bees box and are best for cavity nesting bees. The best “bang for your buck” focuses on ground-nesting habitat protection/restoration (i.e. undisturbed grounds that are bare or lightly vegetated) which benefits most native bees.

Over a two-year period in 2012 & 2013, Fortel and colleagues investigated the effectiveness of man-made nesting structures in sustaining and increasing the native bee population within the Grand Lyon region of France, using bee hotels and soil squares. A total of 58 species were identified within 16 study sites (37 in the soil patches & 21 in the bee hotels). Some of these were native bees to the area, whilst others, like the giant resin bee Megachile sculpturalis, are an invasive species from Central Asia. The authors conclude that these bee hotels are effective in promoting and monitoring solitary bee species. Through intensive management, they can encourage native bees to rehabilitate the area, whilst culling introduced species.

Changes in land use for urbanization and agricultural intensification do not affect the cavity & crevice nesting bees as much as the ground nesters. In the built enviornment, crevices and cavities occur in wood and other substrates (think bricks, plaster and similar materials) in houses, fences, and introduced woody vegetation, providing ample real estate for the native bees’ nest. However, the removal of dead trees and introduction of invasive plant species leads to a loss of native plants that bees rely on for habitat or forage. Life finds a way, and despite the hardships, many solitary bee species can thrive in urbanised areas, making bee hotels an effective rehabilitation tool (investigated by Banaszak-Cibicka and Żmihorski, 2012).

Helping Native Bees: Communal Nesters

The two methods discussed above are used by communal nesting bees, since multiple bees from the same species nest close to one another. Native bees nesting communally (called “gregarious” in scientific literature) are not considered social; multiple adult females of the same species share a common nesting area. Each female constructs her own cells, collects her own food, and lays her own eggs – there is no division of labour or cooperative brood rearing.

Many solitary bees choose to nest near members of the same species, and this nesting proximity can persistent for many generations in some bees (Neff, 2003). The advantages of communal nests are many, and one such aspect is the defence against predators and parasites: the large of number of bees within the habitation zone will deter the approach of these creatures. However, this generates a Catch-22: since there is a large number of bees in one place, then that area can suffer from a disproportionately large number of attacks².

This should not discourage one from helping native bees. Once a communal nest is established, the site proves itself suitable, and bees tend to return to that same location, generation after generation. For many people, hanging bee hotels is an easy starting point for a variety of mason bees, who will populate the existing holes with their nesting material. For those with more acreage, they can look into soil squares from the local area, as described above and in the work of Neumuller & colleagues.

Why Some Solitary Bees Become (Temporary) Social Nesters

Some solitary species may become gregarious as a result of necessity. For example, the slightly-social³ carpenter bees Xylocopa sonoria were found to nest in small groups during the winter (Ostwald et al., 2022).

Adult female carpenter bees remain inactive in tight huddles at the ends of their nesting holes inside tunneled logs (which can be recreated in a bee hotel). Come spring, they become aggressive as the females compete for dominance and ownership of the nest, or depart in search of other suitable nesting sites. This mutual tolerance buffered the bees against the extreme environmental conditions (the harsh winters of the Sonoran desert), and the study found that the bees nesting together had a larger body mass and improved survival the following spring compared to those that nested alone (in this case, nesting alone under laboratory conditions).

How Solitary Bees Survive the Winter

In general, insect survival during winter is linked to thermal conditions: can these bees maintain sufficient insulation to reduce heat loss to the environment? Some may question whether the warmer temperatures would mean an increased metabolic rate and therefore increase energy drain. However temperature variability increases energy drain more than a higher body temperature (Williams et al., 2012). In these solitary-turned-social bees, winter aggregations reduced the impacts of temperature fluctuations, and further reduced the need for shivering thermogenesis- an energetically costly method of generating heat.

Helping Native Bees: Social Nesters

There are other insects in the bee family that are social, and yet honey bees hold the throne. If A. mellifera is native to your area and you would like to help them, look into becoming a beekeeper. If you are from the South East Asian region, you are lucky to have access to many native honey bees within the Apis genera (reviewed in the On the Scientific Name of Bees & nesting habits in The Natural Beehive – go read those articles, find a wild colony and send me photographs, pretty please). The social nesting species examined here are the bumble bees and stingless bees.

Bumble Bees: the Fuzzy Bees

For these species, the easiest fix is to create a floral-rich environment in urban settings, using a variety of exotic and native flowers to provide bees with adequate nutrition for combating disease. The 2020 study by McNeil and colleagues surveyed pathogen levels in bumble bees over two years from various parts of habitats in Pennsylvania, and found that the bumble bees from “low-quality landscapes exhibited the highest pathogen loads”. Low-quality landscapes were defined as “low varieties of spring floral resources and nesting habitats, and a higher honey bee colony density” (despite pollinating plants in different ways, the generalist nature of both bee species puts them at competition with one another).

Laboratory studies have shown that bumble bees had a higher rate of mortality from viral diseases when starved, and this nutritional deprivation is a consequence of poor forage, resulting in reduced immune gene expression (Manley et al., 2017). Such findings are unsurprising, and they can be extrapolated to other bees like the stingless bees, who would also suffer from poor floral environments and nutritional deficiencies.

Stingless Bees: the Small Native Bees

In Australia, tropical rainforest fragmentation altered the nesting habits of the social stingless bees Tetragonula carbonaria. These cavity-nesting bees are smaller than the honey and bumble bees, living in colonies (10,000 workers to a queen), pollinating numerous native plants as well as a variety of tropical and subtropical crops (Smith & Mayfield, 2018). This reduction in rainforest density reduced the number of suitable trees for colonies to build nests, which had downstream effects of reducing floral availability.

In 2016, Carrié & colleagues suggested that bee body size negatively correlated with proximity to semi-natural [human settlements] areas. In such circumstances, smaller-bodied bees must live closer to their food source, as these bees have a lower dispersal when it comes to foraging distances (and by extension, finding suitable wood, soil, water and other non-floral aspects).

Native Beekeeping in Australia

Keeping social native bees is a business in Australia. Residents are able to purchase specially-designed beehives for keeping native pollinators like Austroplebeia Australis or Tetragonula Hockingsi & Tetragonula carbonaria. Much like getting started in A. mellifera beekeeping, a Google search will show you the variety of materials, techniques and benefits for keeping native bees, as well as their benefits to the environment. While they produce small amounts of honey (seriously small – less than a kilogram per year), they are said to have a unique taste that makes for excellent recipes.

For those interested in helping social native bees within their region, get started by searching if similar hive and artificial nests designs exist. Unlike regular beekeeping, keeping native bees is bound to have little, if any regulations as they are not considered livestock or agricultural assets.

Not Helping Native Bees: Cuckoo Bees

Special mention to the cuckoo bees: a parasitic species of solitary bees that do not construct nests of their own, and use established nests of other solitary bees to lay eggs and raise brood. If you are interested in helping cuckoo bees, then continue creating the suitable nesting soil and bee hotels described above. As more solitary bees are attracted to build nests in these artificial sites, the cuckoo bees will appear to infiltrate the nests for their hard-earned pollen and nectar. When you do spot them, be sure to send photographs for your humble author!

Cuckoo larvae tend to hatch before the host larvae, where they proceed to consume the pollen and nectar gathered by the unsuspecting females. The larvae then pupate and emerge as adult cuckoo bees, leaving the original host larvae an empty nest and death by starvation (some eggs do not hatch at all, as several cuckoo species are known destroy the host eggs prior to laying their own [Rozen 2003]).

Despite being parasitic and gruesome, cuckoo bees remain a type of native bee species, and the fact that it has survived to the present day shows that their reproductive strategies are effective at producing successive generations.

Native Bees are Specialists, Rarely Generalists

There’s more to native bees than flower visitations. Solitary species also depend on non-floral factors like soil temperature, substrate, composition and compaction. Changes in land use, systemic insecticides use, as well as the introduction of exotic flowering plants and fruit trees over a relatively short period of time have created rapid selection pressures on native bees. As a result, the native bee species referred to as “oligolectic” (i.e. depending exclusively on one or a few plant types for pollen and nectar) are becoming rarer in urban and agricultural environments compared to their generalist counterparts, the “polylectic” bees, who gather pollen and nectar from a diverse group of plant species.

This article provided several low-maintenance and easy-to-perform “methods “Do’s” to help bees. There are also the ” don’ts””: Avoid using pesticides and fungicides where possible, avoid garden & soil disruption (planting/digging etc…) during nesting seasons, and likewise with mowing & landscape maintenance. It’s a big ask, I know, with neighbours and aesthetics and all – maybe you can opt for leaving leaf litter or bare spots undisturbed for ground nesters?

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Footnotes

1. Local soil is used to match the needs of the local native bee community, so don’t run off to the hardware store in hopes of constructing hills out of potting soil! (Actually, this could work within the barren landscape that is the metropolis…). ↩︎
2. The 2005 study by Polidori and colleagues showed the satellite flies Leucophora personata and scuttle flies Megaselia andrenae concentrating their parasitic activities on zones that had the highest nesting density of the mining bees Andrena agilissima. ↩︎
3. The formal term is “Facultatively Social Species”, which defines “a species’ capacity for plasticity in its social organization” (Reviewed in Shell & Rehan, 2018). This is not the same as the sociability of honey bees, and is generally driven by circumstances rather than genetics. You’ll find several examples in Section 2 of the aforementioned review article. ↩︎