Using citizen science to examine the nesting ecology of ground‐nesting bees

Suitable nest sites are a crucial habitat requirement of ground‐nesting bees, but empirical studies of fossorial solitary bee nesting ecology in the UK are few in number. This study used a citizen science approach to overcome the logistical and temporal barriers associated with this type of research and to gather data on the abiotic environment associated with the nesting aggregations of four fossorial solitary bee species in the UK. Three hundred and ninety‐four records were submitted by the public between March and November 2017. Sixty percent (236) of these records were verified as indicative of active nesting aggregations of the target species. Overall, the species in this study demonstrated the capacity to nest within a broad range of environmental variables. Although Colletes hederae (Schmidt and Westrich 1993) was often reported from sloped, unshaded sites, and Andrena fulva (Müller in Allioni 1766) was regularly associated with flat, shaded locations. This study demonstrated the efficacy of a citizen science approach in surmounting the intrinsic difficulties associated with studying solitary bee nest sites, which are both ephemeral and cryptic structures in the landscape. Solitary bees constitute roughly 250 species of wild bee in the UK, but there remain significant knowledge gaps with regard to their ecology (Wood et al. 2016). This group encompasses many important pollinators, including those of high‐value crops such as apples (Garratt et al. 2016), but is facing diversity loss (Biesmeijer et al. 2006), declines in relative abundance (Bartomeus et al. 2013), and extinctions (Ollerton et al. 2014). There are two principal resources that solitary bee populations require in order to survive and proliferate: suitable and robust nest sites for their offspring to successfully mature in, and sufficient forage material both for their own survival and to provision their young. The foraging requirements of bees have been well studied (Strickler 1979, MacIvor et al. 2014, Dicks et al. 2015, Wood et al. 2016) as they are believed to be the principal limiting resource. However, within a landscape, Gathmann and Tscharntke (2002) have speculated that nest sites may be a limiting factor for solitary bees more often than forage, although it is clear that these resources must work in tandem. There is a lack of empirical research regarding the nesting requirements of fossorial solitary bees in the UK (but see Potts and Willmer 1997). Although there are multiple reasons for this gap, the difficulties associated with finding sufficient nest sites in the field and