The blood or hemolymph, as in other arthropods, is carried in an open circulatory system.[3] The body organs, "heart" (dorsal aorta), muscles, etc. are surrounded in a reservoir of blood, and pulsing contractions of the tube-like dorsal aorta create a weak circulatory force.

In fertilised queens the ovaries are activated when the queen lays her egg. It passes along the oviduct to the vagina. In the vagina there is a chamber called the spermatheca. This is where the queen stores sperm from her mating. The queen, depending on need, may allow her egg to be fertilised. Non-fertilised eggs become males, and only fertilised eggs grow into females and queens.

As in all animals, hormones play a significant role in the growth and development of the bumblebee. The hormones that stimulate the development of the ovaries are suppressed in female worker bees, while the queen remains dominant. Salivary glands in the head secrete saliva, which mixes with the nectar and pollen. Saliva is also mixed into the nest materials to soften them. The body fat is a nutritional store; before hibernation, queens eat as much as they can to enlarge their fat body, and the fat in the cells is used up during hibernation.
A bumblebee Bombus pascuorum extending its tongue towards a Heuchera inflorescence

Like all bee tongues, the bumblebee tongue (the proboscis) is a long hairy structure that extends from a sheath-like modified maxilla. The primary action of the tongue is lapping, i.e. repeated dipping of the tongue into liquid.[4] During lapping, nectar is drawn up the proboscis by capillary action. When at rest or flying, the proboscis is kept folded under the head. The exoskeleton of the abdomen is divided into plates called dorsal tergites and ventral sternites. Wax is secreted from glands on the sternites.

The brightly coloured pile of the bumblebee is a form of aposematic signal. Depending on the species and morph, these colours 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 because it is better grounded than the other parts of the flower.

Bumblebees do not have ears; however, they can feel the vibrations of sounds through nearby materials.
Habitat

Bumblebees are typically found in higher latitudes and/or high altitudes, though exceptions exist (there are a few lowland tropical species).[5] A few species (Bombus polaris and B. alpinus) range into very cold climates where other bees might not be found; B. polaris can be found in northern Ellesmere Island—the northernmost occurrence of any eusocial insect—along with its parasite, B. hyperboreus.[6] One reason for this is that bumblebees can regulate their body temperature, via solar radiation, internal mechanisms of "shivering" and radiative cooling from the abdomen (called heterothermy). Other bees have similar physiology, but the mechanisms have been best studied in bumblebees.[7]
Nests
File:Bumblebee nest with bumblebee Queen.ogv
Bombus terrestris inside an artificial pollination nest, the queen rocks her wings.

Bumblebees form colonies, which 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, the responsibility of a single female 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. Bumblebee nests may be found within tunnels in the ground made by other animals, or in tussock grass as opposed to Carpenter Bees that burrow into wood. Bumblebees sometimes construct a wax canopy ("involucrum") over the top of their nest for protection 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. The queens can live up to one year, possibly longer in tropical species.
Colony cycle

Bumblebee nests are first constructed by over-wintered queens in the spring (in temperate areas). 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 bumblebee species, with some species preferring to nest in underground holes and others in tussock grass or directly on the ground. Once the queen finds a site, she prepares wax pots to store food, and wax cells to lay eggs in. These eggs then hatch into larvae, which cause the wax cells to expand isometrically into a clump of brood cells.
A bumblebee Bombus terrestris enlarging her nest hole

To develop, these larvae must be fed both nectar for carbohydrates and pollen for protein. Bumblebees feed nectar to the larvae by chewing a small hole in the brood cell into which they regurgitate nectar. Larvae are fed pollen in one of two ways, depending on the bumblebee species. So-called "pocket-maker" bumblebees create pockets of pollen at the base of the brood-cell clump that the larvae feed themselves from. Conversely, "pollen-storers" store pollen in separate wax pots and feed it to the larvae in the same fashion as nectar.[8] Bumblebees are incapable of trophallaxis (direct transfer of food from one bee to another).

With proper care, the larvae progress through four instars, becoming successively larger with each moult. At the end of the fourth instar, the larvae spin silk cocoons under the wax covering the brood cells, changing them into pupal cells. The larvae then undergo an intense period of cellular growth and differentiation and become pupae. These pupae then develop into adult bees, and chew their way out of the silk cocoon. When adult bumblebees first emerge from their cocoons, the hairs on their body are not yet fully pigmented and are a greyish-white colour. The bees are referred to as "callow" during this time, and they will not leave the colony for at least 24 hours. The entire process from egg to adult bee can take as long as five weeks, depending on the species and the environmental conditions.

After the emergence of the first or second group of workers, workers take over the task of foraging and the queen spends most of her time laying eggs and caring for larvae. The colony grows progressively larger and at some point will begin to produce males and new queens. The point at which this occurs varies among species and is heavily dependent on resource availability and environmental factors. Unlike the workers of more advanced social insects, bumblebee workers are not physically reproductively sterile and can lay haploid eggs that develop into viable male bumblebees. Only fertilised queens can lay diploid eggs that mature into workers and new queens.

Early in the colony cycle, the queen bumblebee compensates for potential reproductive competition from workers by suppressing their egg-laying by way of physical aggression and pheromonal signals.[9] Thus, the queen will usually be the mother of all of the first males laid. Workers eventually begin to lay male eggs later in the season when the queen's ability to suppress their reproduction diminishes.[10] The reproductive competition between workers and the queen is one reason that bumblebees are considered "primitively eusocial".

New queens and males leave the colony after maturation. Males in particular are forcibly driven out by the workers. Away from the colony, the new queens and males live off nectar and pollen and spend the night on flowers or in holes. The queens are eventually mated (often more than once) and search for a suitable location for diapause (dormancy).
Foraging behaviour
Further information: Bumblebee communication
Biting open the stem of a flower...
...and using its tongue to drink the nectar.
A Bumblebee "nectar robbing" a flower
A bumblebee loaded with pollen in its pollen baskets

Bumblebees generally visit flowers that exhibit the bee pollination syndrome. They can visit patches of flowers up to 1–2 kilometres from their colony.[11] Bumblebees will also tend to visit the same patches of flowers every day, as long as they continue to find nectar and pollen,[12] a habit known as pollinator or flower constancy. While foraging, bumblebees can reach ground speeds of up to 15 metres per second (54 km/h).[13]

Experiments have shown that bumblebees use a combination of colour and spatial relationships to learn which flowers to forage from.[14] Bumblebees can also detect both the presence and the pattern of electric fields on flowers, which occur due to the positive static charges that are generated when bees fly through the air (see Atmospheric electricity), and take a while to leak away into the ground. They use this information to find out if a flower has been recently visited by another bee.[15] After arriving at a flower, they extract nectar using their long tongue ("glossa") and store it in their crop. Many species of bumblebee also exhibit what is known as "nectar robbing": instead of inserting the mouthparts into the flower normally, these bees bite directly through the base of the corolla to extract nectar, avoiding pollen transfer.[16] These bees obtain pollen from other species of flowers that they "legitimately" visit.

Pollen is removed from flowers deliberately or incidentally by bumblebees. Incidental removal occurs when bumblebees come in contact with the anthers of a flower while collecting nectar. The bumblebee's body hairs receive a dusting of pollen from the anthers, which is then groomed into the corbicula ("pollen basket"). Bumblebees are also capable of buzz pollination.

In at least a few species, once a bumblebee has visited a flower, it leaves a scent mark on the flower. This scent mark deters visitation of the flower by other bumblebees until the scent degrades.[17] It has been shown that this scent mark is a general chemical bouquet that bumblebees leave behind in different locations (e.g. nest, neutral, and food sites),[18] and they learn to use this bouquet to identify both rewarding and unrewarding flowers.[19] In addition, bumblebees rely on this chemical bouquet more when the flower has a high handling time (i.e. it takes a longer time for the bee to find the nectar).[20]

Once they have collected nectar and pollen, bumblebees return to the nest and deposit the harvested nectar and pollen into brood cells, or into wax cells for storage. Unlike honey bees, bumblebees only store a few days' worth of food and so are much more vulnerable to food shortages.