We investigate whether the eye parameter of bumblebees—a visual trait measuring the tradeoff between light sensitivity and visual resolution—is associated with: (i) local habitats, (ii) forest cover at the landscape scale (1 km radius), and (iii) the shade tolerance of the plants they forage on. The association of bumblebee species with local habitat and forest cover at the landscape scale was analyzed using generalized linear mixed models. We combined data from the Norwegian national bumblebee monitoring program with Corine CLC+ land cover and bumblebee functional traits: eye parameter and intertegular distance. These analyses were done at the species and community level. To determine whether bumblebee light sensitivity correlated with the shade tolerance of the plant they forage on, we combined bumblebee–plant interactions from a British database with a Swedish plant trait database. Our findings showed that bumblebee species with high light sensitivity were more common and abundant in forest habitats and areas with greater forest cover, while species with high visual resolution showed the opposite trend. This pattern was reflected at the community level, as indicated by the community-weighted mean of the eye parameter, which increased with forest cover and was higher in forest habitats. Furthermore, bumblebees with higher light sensitivity tended to forage on plants with greater shade tolerance. These results suggest that visual adaptations for light sensitivity contribute to shaping bumblebee species distributions across different scales. Our study underscores the importance of pollinator vision in understanding species niches and its value for species distribution modeling. Moreover, by relating pollinator visual abilities to plant niches for the first time, this study provides an important basis for future modeling of plant–pollinator interactions and targeted conservation measures for plants and pollinators in forested landscapes.

Environmental heterogeneity in forest understories creates microhabitat niches that differ both spatially and temporally in light intensity and temperature. Do animal communities segregate in relation to these niche dimensions, and can this be explained by functional traits? Answering these questions is particularly important for insect pollinators, as they play a critical role in maintaining flowering plant biodiversity. Bumblebees are essential pollinators of high altitude/latitude ecosystems and are particularly sensitive to climate change. In early spring, they forage on bilberry, a keystone species in heterogeneous habitats – hemi-boreal forests. We capitalised on these conditions to study a species-specific selection of foraging niches in relation to abiotic conditions. We combined full-day monitoring of bumblebee communities foraging in bilberry-dominated forests with joint species distribution modelling, which showed that temperature conditioned species occurrence, while light intensity explained species abundance. The inclusion of functional traits did not improve the overall explanatory and predictive power of the models. Our results suggest that temperature acts as a first filter of the local species pool and that species, once present, partition along a light intensity gradient. This study confirms and extends upon previous findings that microhabitat partitioning may act as a mechanism underpinning bumblebee coexistence. It highlights the importance of focusing on micro-scales when studying how species interact with their environment, as this could, for example, help improve our ability to predict the consequences of global changes.

Over the past decades, increasing environmental temperatures have been identified as one of the causes of major insect population declines and biodiversity loss. However, it is unclear how these rising temperatures affect endoheterothermic insects, like bumblebees, that have evolved thermoregulatory capacities to exploit cold and temperate habitats. To investigate this, we measured head, thoracic, and abdominal temperature of bumblebee (Bombus terrestris) workers across a range of temperatures (24 °C–32 °C) during three distinct behaviors. In resting bumblebees, the head, abdomen, and thorax conformed to the environmental temperature. In pre-flight bumblebees, the head and abdominal temperatures were elevated with respect to the environmental temperature, while the thoracic temperature was maintained, indicating a pre-flight muscle warming stage. In post-flight bumblebees, abdominal temperature increased at the same rate as environmental temperature, but the head and the thoracic temperature did not. By calculating the excess temperature ratio, we show that thermoregulation in bumblebees during flight is partially achieved by the active transfer of heat produced in the thorax to the abdomen, where it can more easily be dissipated. These results provide the first indication that the thermoregulatory abilities of bumblebees are plastic and behavior dependent. We also show that the flight speed and number of workers foraging increase with increasing temperature, suggesting that bees do not avoid flying at these temperatures despite its impact on behavioral performance.

Like many insects, bumblebees use polarized light (PL) to orient and navigate. The celestial PL pattern is strongest when the sun is close to the horizon, during the dim light of dawn and dusk. In the dim light, the sensitivity of the compound eyes may not be sufficient for detecting PL or landmarks, and it has previously been hypothesized that bumblebees rely on PL from their more sensitive ocelli to navigate at dawn and dusk. Here, we tested this hypothesis using a combination of electrophysiological and behavioural tests. Specifically, we investigate whether bumblebee ocelli can detect PL and explore how the PL contribution from the ocelli and compound eyes is affected by light intensity. We find that bumblebee ocelli do indeed have PL sensitivity and that PL information can be used to guide behaviour in dim light. In bright light, however, both the compound eyes and ocelli are important for the detection of PL. Our results support the hypothesis that bumblebees use PL information from the ocelli at the low light levels that occur around dawn and dusk, and this may support their ability to forage during these periods.

A rare sighting of two male carrion specialist dung beetles, Scarabaeolus carniphilus Deschodt & Davis, 2015, burying a freshly dead Herald snake (Crotaphopeltis hotamboeia (Laurenti, 1768)) is documented from its discovery in the field and subsequent reburial under laboratory conditions. The species studied is a member of the telecoprid (dung roller) Scarabaeini, but behaved here like a paracoprid; it deliberately cut into and removed flesh from the dead snake; these pieces were then taken into a feeding burrow; later a pheromone release stance was taken up near an established burrow; and under laboratory conditions the snake was completely buried. These observations, mostly novel for this species and its genus are clearly documented via photographs and an online time lapse video taken every hour for 24-hours during the snake's-(re)burial. This note introduces relevant aspects of dung beetle natural history and new biological information for Scarabaeolus and particularly for Sc. carniphilus. It records and interprets a carrion specialist Scarabaeini dung beetle burying and feeding on fresh carrion; highlights natural history findings (pheromone release) previously not considered for the evolution of the Scarabaeini; and aims to stimulate behavioural research into this interesting and under studied genus Scarabaeolus.

The most effective way to avoid intense inter- and intra-specific competition at the dung source, and to increase the distance to the other competitors, is to follow a single straight bearing. While ball-rolling dung beetles manage to roll their dung balls along nearly perfect straight paths when traversing flat terrain, the paths that they take when traversing more complex (natural) terrain are not well understood. In this study, we investigate the effect of complex surface topographies on the ball-rolling ability of Kheper lamarcki. Our results reveal that ball-rolling trajectories are strongly influenced by the characteristic scale of the surface structure. Surfaces with an increasing similarity between the average distance of elevations and the ball radius cause progressively more difficulties during ball transportation. The most important factor causing difficulties in ball transportation appears to be the slope of the substrate. Our results show that, on surfaces with a slope of 7.5 deg, more than 60% of the dung beetles lose control of their ball. Although dung beetles still successfully roll their dung ball against the slope on such inclinations, their ability to roll the dung ball sideways diminishes. However, dung beetles do not seem to adapt their path on inclines such that they roll their ball in the direction against the slope. We conclude that dung beetles strive for a straight trajectory away from the dung pile, and that their actual path is the result of adaptations to particular surface topographies.

Understanding how ecological communities assemble in relation to natural and human-induced environmental changes is critical, particularly for communities of pollinators that deliver essential ecosystem services. Despite widespread attention to interactions between functional traits and community responses to environmental changes, the importance of sensory traits has received little attention. To address this, we asked whether visual traits of bumblebee communities varied at large geographical scales along a habitat gradient of increased tree cover. Because trees generate challenging light conditions for flying insects, in particular a reduced light intensity, we hypothesised that differences in tree cover would correlate with shifts in the visual and taxonomical composition of bumblebee communities. We quantified 11 visual traits across 36 specimens from 20 species of bumblebees using micro-CT and optical modelling of compound eyes and ocelli, and investigated how these traits scale with body size. Using an inventory of bumblebee communities across Sweden and our visual trait dataset, we then explored how visual traits (both absolute and relative to body size) differed in relation to tree cover. We found positive shifts of the community weighted means of visual traits along the increasingly forested habitat gradient (facet diameter, inter-ommatidial angle, eye parameter of the compound eye and alignment of the three ocelli) that were consistent regardless of body size, while other traits decreased when more forest was present in the landscape (facet number). These functional patterns were associated with differences in the abundance of six common species that likely explains the community-wide shift of visual traits along the habitat gradient. Our study demonstrates the interaction between vision, habitat and community assembly in bumblebees, while highlighting a promising research topic at the interface between sensory biology and landscape ecology.

Eusocial insect colonies act as a superorganism, which can improve their ability to buffer the negative impact of some anthropogenic stressors. However, this buffering effect can be affected by anthropogenic factors that reduce their colony size. A reduction in colony size is known to negatively affect several parameters like brood maintenance or thermoregulation, but the effects on behaviour and cognition have been largely overlooked. It remains unclear how a sudden change in group size, such as that which might be caused by anthropogenic stressors, affects individual behaviour within a colony. In this study, the bumblebee Bombus terrestris was used to study the effect of social group size on behaviour by comparing the associative learning capabilities of individuals from colonies that were unmanipulated, reduced to a normal size (a colony of 100 workers) or reduced to a critically low but functional size (a colony of 20 workers). The results demonstrated that workers from the different treatments performed equally well in associative learning tasks, which also included no significant differences in the learning capacity of workers that had fully developed after the colony size manipulation. Furthermore, we found that the size of workers had no impact on associative learning ability. The learning abilities of bumblebee workers were thus resilient to the colony reduction they encountered. Our study is a first step towards understanding how eusocial insect cognition can be impacted by drastic reductions in colony size. Significance statement While anthropogenic stressors can reduce the colony size of eusocial insects, the impact of this reduction is poorly studied, particularly among bumblebees. We hypothesised that colony size reduction would affect the cognitive capacity of worker bumblebees as a result of fewer social interactions or potential undernourishment. Using differential conditioning, we showed that drastic reductions in colony size have no effect on the associative learning capabilities of the bumblebee Bombus terrestris and that this was the same for individuals that were tested just after the colony reduction and individuals that fully developed under the colony size reduction. We also showed that body size did not affect learning capabilities. This resilience could be an efficient buffer against the ongoing impacts of global change.

Bumblebees are important pollinators, that are declining rapidly in number and need urgent protection. Visual cues are extremely important for bumblebee activities and survival so a full understanding of the micro-and nano-structure of their eyes will help us to better understand their vision and how it is affected by rapid habitat changes. Here, we present the first report on imaging of 3D structures with sub-100 nm resolution of an unstained bumblebee compound eye using X-ray holographic tomography. This study demonstrates the potential of using X-ray nano-tomography for bulk samples for zoological studies on insects. Compared to the other commonly used methods, such as TEM and FIB-SEM, X-ray nanoCT is non-destructive and relatively fast, and has the potential for providing a better understanding of a broad range of biological materials.