Western honey bee

Strong evidence derived from the direct study of free-living colonies or indirectly through investigations on managed ones suggests that unaided colonies face a barrage of threats that can significantly impact their survival in the wild. From these studies, it has been determined that wild, self-sustaining A. mellifera populations in Europe have been greatly impacted and are now considered rare or locally extinct. The primary threats to the survival of wild Honey Bee populations are listed below:

Habitat loss and malnutrition
Intensive land use for agriculture, commercial, and residential development has led to a decrease in the availability of suitable habitats for wild Honey Bee. In particular, one of the major limiting factors is represented by the decrease of forest habitats harbouring large trees capable of hosting cavities suitable for nesting free-living colonies (Requier et al. 2020). Hollow trees situated along tree-lined roads (i.e., avenues) are being removed as part of modernisation efforts and for safety reasons (Oleksa et al. 2013). Moreover, there is generally high competition among species for occupying such cavities, which usually leads to depredation of Honey Bee nests in winter (Kohl et al. 2023).

The lack of floral resources (pollen and nectar) in the environment may impact food reserves and decrease a colony’s survival, especially over winter. Rutschmann et al. (2022) found a positive correlation between the abundance and winter survival of Honey Bee colonies and the proportion of semi-natural habitats (woodland and shrubland) in the surrounding area. This suggests that semi-natural habitats are essential for the survival and conservation of free-living Honey Bees. Therefore, conversion of these habitats for agricultural or other human activities poses a continued threat to wild Honey Bee populations. Maintaining and increasing semi-natural habitats such as woodlands and shrublands could become a viable strategy for conserving free-living Honey Bee populations.

Pathogens, parasites, and predators
Invasive alien species are among the most devastating biotic threats affecting the survival of Honey Bees colonies, both managed and wild.

The ectoparasitic mite Varroa destructor (the Varroa Mite) has been identified as the most likely cause of the demise of wild populations across Europe (Moritz et al. 2007, Jaffé et al. 2010). Varroa was introduced in Europe in the 1960s and rapidly spread across the entire continent and most islands (Traynor et al. 2020). V. destructor affects the health of the western Honey Bee both directly and indirectly. It causes direct damage to developing larvae and pupae by feeding on their fat body, thereby interfering with two fitness components of the Honey Bee: (i) vitality: it lowers immune response and healing mechanisms, as well as alters flying, homing, and orientation abilities in foragers; (ii) reproduction: lowers adults’ weight, causing a reduction in spermatozoids production in males (Noël et al. 2020). Even more severely, it causes indirect damage, serving as a reservoir and vector of several harmful viruses, most notably Deformed Wing Virus (Noël et al. 2020). The few molecular viral surveys carried out on free-living colonies in Europe detected several viruses that are also common in managed colonies. The results are variable, with studies detecting similar, lower, and higher prevalence/loads of different viruses in free-living compared to managed colonies (Thompson et al. 2014, Kohl et al. 2022).

The fungal pathogen Nosema ceranae (Nosema disease) was first documented infecting the Honey Bee in Europe in 2004 (Higes et al. 2006), but it is possible that it arrived earlier. It has been detected in managed colonies all over Europe and has also spread to free-living colonies (Thompson et al. 2014, Łopieńska-Biernat et al. 2017). N. ceranae infects honey bees’ midgut cells and consumes their contents via phagocytosis. It can reduce Honey Bee’ fitness by (i) decreasing lifespan and nursing ability, (ii) inducing precocious foraging, and (iii) affecting olfactory learning, memory, and flight. All these effects can reduce colony size, honey reserves, and brood-rearing capacity, eventually leading to colony demise. N. ceranae seems to cause more harm to colonies in the warmer Mediterranean regions than in the colder climates of northern Europe (Martín-Hernández et al. 2018).

The Honey Bee predator, the Asian Hornet (Vespa velutina), was first sighted in Europe in southwestern France in 2004, and has since expanded across Western Europe, from southern Portugal to the Netherlands and across the English Channel into Great Britain. It is also spreading eastwards to Italy (see the dynamic map at frelonasiatique.mnhn.fr). In this vast non-native area, the Asian Hornet is causing substantial colony losses in managed apiaries, and it is also likely impacting free-living colonies, as it frequently nests in forest habitats. It feeds on many insects but intensifies its predation on Honey Bees from the end of summer to the winter (Requier et al. 2019). In addition to predation, another deleterious impact on colonies occurs in the autumn, when hundreds of hornets hover at the entrance of a colony, disrupting foraging and, thus, interfering with the colony’s winter preparations and sometimes causing starvation (Laurino et al. 2019, Requier et al. 2019).

The Small Hive Beetle (Aethina tumida) is an invasive species that infests Honey Bee colonies and causes the collapse of wax combs and destruction of honey stores, as a result of uncontrolled reproduction inside the nest (Neumann et al. 2016). It was first sighted in Europe in 2014, in managed colonies in the province of Reggio Calabria, Italy. There were also outbreaks in eastern Sicily in 2014 and 2019. Although eradication has not been achieved, restrictive measures have prevented its spread throughout Europe (Mutinelli et al. 2014). Currently, the species is confined to a limited area in Calabria (Federico et al. 2025).

Lastly, the invasive ectoparasitic mite (Tropilaelaps mercedesae), a novel and devastating pest for Western Honey Bee, has recently been reported in managed colonies in Europe (Brandorf et al. 2024, Janashia et al. 2024). Infestation by this mite can lead to drastic losses, as it feeds on brood and can transmit bee viruses (Chantawannakul et al. 2018). Given its successful spread among managed colonies, the mite is expected to be able to infest free-living colonies too, as in the case of Varroa. Its further spread will therefore represent a significant factor limiting the survival of wild Honey Bees in Europe.

Possible effects of beekeeping practices
Some modern beekeeping practices could impact wild A. mellifera populations (Panziera et al. 2022), including: the commercial trade in queens (leading to introgression and threatening the genetic integrity of native populations and subspecies) as well as migratory beekeeping and large-scale selective breeding (which can contribute to the loss of genetic diversity, rendering the species more vulnerable to diseases and environmental changes) (De la Rúa et al. 2009, Pinto et al. 2014, López-Uribe et al. 2017, Requier et al. 2019, Espregueira Themudo et al. 2020, Tanasković et al. 2021, Martínez-López et al. 2022).

The international trade of queens and long-distance migratory beekeeping, the extent of which has increased dramatically over the last century, have promoted the spread of non-local Honey Bee subspecies and those produced through the artificial crossing of multiple subspecies. These practices favour the use and persistence of less viable and locally unsuitable genotypes (Büchler et al. 2014, Meixner et al. 2015, Fontana et al. 2018). Given that Honey Bee mating cannot be fully controlled by beekeepers, and considering the high density of managed colonies in Europe, such maladapted genotypes are likely to have already been introduced into free-living populations, thereby impacting their gene pools and ultimately their survival.

Pesticides, herbicides, and fungicides
Pesticides, herbicides, and fungicides may detrimentally impact the forage availability of A. mellifera (Henry et al. 2012, Prado et al. 2019, Barascou et al. 2022) as well as Honey Bee health (Blacquière et al. 2012). So far, no specific study has been carried out on the effects of exposure of free-living colonies to pesticides. However, colonies nesting in intensive agricultural areas, where these compounds are intensively used, were found to have lower winter survival rates than colonies in semi-natural areas (Rutschmann et al. 2022).

Further research on free-living colonies is urgently needed in order to identify self-sustaining populations and to understand the status of populations across the whole Pan European level, focusing on data-poor parts, such as the far Eastern regions. This could be achieved through population ecology studies based on repeated genotyping of colonies and long-term monitoring of their nests to infer demographic parameters at the population level (e.g., Kohl et al. 2022, Moro et al. 2024). Furthermore, research should also focus on gaining a more profound comprehension of the threats impacting such populations. Given the present research gap, acquiring such data is essential and will play a pivotal role in facilitating conservation efforts, potentially driving reforms in both national and international policies (Panziera et al. 2022).

Notably, this research could begin (or continue) by monitoring, sampling, and testing the nest locations gathered for this present assessment (see map produced within this report). Additionally, researchers and citizen scientists can contribute data to Honey Bee Watch and/or to the various initiatives that collected these data points (see below).

In response to the urgent need for data on free-living colonies, an international coalition of researchers and stakeholders focused on free-living Honey Bees was established in 2019 to locate, monitor, study, and protect wild A. mellifera populations. Honey Bee Watch‘s mission is to create an extensive repository of data, protocols, and resources pertaining to free-living colonies, which will be used to empower further research and enable conservation endeavours.

For this reassessment, HBW acknowledges the contributions of numerous partners involved in the study of free-living Honey Bee colonies in Europe, who, along with other initiatives, shared data for building a map of confirmed sightings of free-living colonies in Europe (see Geographic Range section):

• BEEtree-Monitor, Germany
• Blenheim Palace and Estate, United Kingdom
• Boomtreebees, Ireland
• Boughton Estate Honeybee Conservation Project, United Kingdom
• Edmund Mach Foundation, Italy
• Galway Honey Bee Research Centre, University of Galway, Ireland
• Honey Bee Wild, Luxembourg
• Honungsbiföreningen, Sweden
• Instituto Politécnico de Bragança, Portugal
• Kazimierz Wielki University, Poland
• Nature Research Centre, Lithuania
• Office pour les insectes et leur environnement (OPIE), France
• Resilient Bee Project, Italy
• Slovak University of Agriculture in Nitra, Slovakia
• UMR CNRS-IRD-Université Paris-Saclay, France

• University of Belgrade, Serbia
• University of Sussex, United Kingdom
• University of Würzburg, Germany
• Wild Bees Project, France

In addition to the groups listed above, other initiatives are also surveying and/or monitoring free-living colonies in Europe (e.g., FreeTheBees, Swiss BeeMapping, Dortmund free-living colonies study, etc.), but were not able to or chose not to share data for this reassessment due to a variety of reasons.

Immediate measures considered beneficial for the preservation of wild A. mellifera populations include (i) ensuring the conservation of natural habitats rich in suitable nesting cavities (Oleksa et al. 2013, Kohl and Rutschmann 2018, Requier et al. 2020, Rutschmann et al. 2022), (ii) controlling the spread of invasive Honey Bee predators and parasites, and (iii) promoting the use of native and regional subspecies for beekeeping to avoid non-native genotypes introgression in local wild subpopulations. The latter recommendation is particularly promoted by the International Association for the Protection of the European Dark Bee (SICAMM), the Native Irish Honey Bee Society (NIHBS), and have been endorsed in Italy through the San Michele All’Adige and the Pantelleria declarations (Fontana et al. 2018, 2022), as well as by the Berlin Declaration on Wild Western Honey Bee Conservation in Europe. National-level strategies in line with these objectives also include the legal restriction on the importation of queens of non-native subspecies, which are already active in Serbia, Slovenia, and the Canary Islands, and under consideration in Ireland.