page_title: Bombus ternarius
section_title: Foraging
hierarchical_section_title: Bombus ternarius / Behavior / Foraging
caption_attribution_description: English: Bombus ternarius, a.k.a. Orange-belted Bumblebee, by the Bow River in Calgary, Alberta, Canada.
context_page_description: Bombus ternarius, commonly known as the orange-belted bumblebee or tricolored bumblebee, is a yellow, orange and black bumblebee. It is a ground-nesting social insect whose colony cycle lasts only one season, common throughout the northeastern United States and much of Canada. The orange-belted bumblebee forages on Rubus, goldenrods, Vaccinium, and milkweeds found throughout the colony's range. Like many other members of the genus, Bombus ternarius exhibits complex social structure with a reproductive queen caste and a multitude of sister workers with labor such as foraging, nursing, and nest maintenance divided among the subordinates.
context_section_description: Flight for bumblebees is energy costly.  Estimates put bumblebee metabolic rate at extremes surpassing even hummingbird metabolic rates, so efficient foraging and good decision-making is paramount or the workers risk a net loss of energy. Pollen is rich in protein necessary to sustain flight, but is more difficult to collect than nectar. Bumblebees exhibit individual learning. New pollen foragers tend to return lighter from about the first 10 foraging trips, allowing foraging efficiency to increase, until it plateaus at about 30 trips. Furthermore, bumblebees tend to collect pollen when conditions are dry and humidity is lower, presumably because pollen clumps are drier then, making foraging easier.  For this reason, more experienced and older workers tend to collect pollen. This approach means inexperienced foragers waste less energy and more pollen is returned to the nest, maximizing the colonies' evolutionary success.
  Little is known about its precise foraging range, but bumblebees' range is, on average, up to 6 km (3.7 mi) which can be extended to far away as 20 km (12 mi) when resources are scarce. One would predict that food patches nearest to the nest would be most visited, so would offer the least uncollected nectar and pollen. A trade-off occurs between energy expenditure in flight and the competition between workers. This effect pushes workers to explore further away from the nest to forage. Some propose that bumblebees venture out farther past their nest because foraging near the nest could bring unwanted attention from predators and consequently risk the success of the colony. This predator hypothesis, however, is often dismissed as showing little effect on bumblebee foraging range.
  A bumblebees often does not fill its nectar crop to full capacity when foraging. This phenomenon is best explained by the marginal value theorem. The weight of nectar in the nectar crop adds an additional energetic cost to flight, so a heavily loaded bumblebee expends significantly more energy to the point of diminishing returns. Depending on the flight distance, a fully filled crop may cause a bumblebee to burn more energy than a partially filled crop would bring back.
caption: B. ternarius foraging on common toadflax (Linaria vulgaris)
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