rom similarly large, fuzzy bees by the form of the female hind leg, which is modified to form a shiny concave surface that is bare, but surrounded by a fringe of hairs used to transport pollen (in similar bees, the hind leg is completely hairy, and pollen grains are wedged into the hairs for transport). Like their relatives the honey bees, bumblebees feed on nectar and gather pollen to feed their young. One characteristic of bees in general is that the body hairs are profusely branched making them more efficient in trapping pollen. Their mouthparts consist of a tube-like proboscis for siphoning the nectar from pants. It is coiled up when not in use.
A Bumbles Bee with Uncoiled Proboscis in Preparation for Removal of Nectar. Image Courtesy FFubs. Right. Bumblebee with Pollen Trapped on Hairs. Image Courtesy of Jesse Hickman
The brightly-colored pile of the bumble bee is a form of aposematic signal, meaning the bright coloration is a sign that I am bad-don’t mess with me (Figure 42). Depending on the species these colors can range from entirely black, to bright yellow, red, orange, white, and pink. Thick pile can also act as insulation to keep the bee warm in cold weather. Further, when flying a bee builds up an electrostatic charge, and as flowers are usually well grounded, pollen is attracted to the bee's pile when it lands. When a pollen covered bee enters a flower, the charged pollen is preferentially attracted to the stigma (female part of plant-thus fertilization occurs) because it is better grounded than the other parts of the flower.
Brightly Colored Bumble Bee. Image Courtesy Christian Sand.
Bumblebees are typically found in higher latitudes and or high altitudes; though exceptions exist (there are a few lowland tropical species). A few species range into very cold climates where other bees might not be found; Bombus. polaris can be found in northern Ellesmere Island (west of Greenland)—the northern most occurrence of any true social insect. One reason for this is that bumblebees can regulate their body temperature, via solar radiation, internal mechanisms of "shivering" and cooling from the abdomen (called heterothermy).
Bumblebee colonies are usually much less extensive than those of honey bees. This is due to a number of factors including: the small physical size of the nest cavity, a single female is responsible for the initial construction and reproduction that happens within the nest, and the restriction of the colony to a single season (in most species). Often, mature bumblebee nests will hold fewer than 50 individuals and are typically found below ground (Figure 43). They sometimes construct a wax canopy over the top of their nest for protection from moisture and insulation. Bumblebees do not often preserve their nests through the winter, though some tropical species live in their nests for several years (and their colonies can grow quite large, depending on the size of the nest cavity). In temperate species, the last generation of summer includes a number of queens who overwinter separately in protected spots.
Bumblebees Nest in a Shed. Image Courtesy Pete Griggs.
Bumblebee nests are first constructed by over-wintered queens in the spring. Upon emerging from hibernation, the queen collects pollen and nectar from flowers and searches for a suitable nest site. The characteristics of the nest site vary among species, with some preferring to nest in underground holes and others in tussock grass or directly on the ground. Once the queen has found a site, she prepares wax pots to store food and wax cells into which eggs are laid. These eggs then hatch into larvae, which cause the wax cells to expand into a clump of brood cells.
These larvae need to be fed both nectar for carbohydrates and protein in order to develop. Bumblebees feed nectar to the larvae by chewing a small hole in the brood cell into which nectar is regurgitated. Larvae are fed pollen in one of two ways, depending on the species. So called "pocket-maker" bumblebees create pockets of pollen at the base of the brood cell clump from which the larva