The Bumblebee

Oct 18, 2009 Features / Columnists, Interesting Creatures in Guyana

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There are over 250 species of bumblebees. They are regarded as social insects that are characterised by black and yellow body hairs, often in bands. However, some species have orange or red on their bodies, or may be entirely black. Another obvious but not unique characteristic is the soft nature of the hair (long, branched setae), called pile, that covers their entire body, making them appear and feel fuzzy. They are best distinguished from similarly large, fuzzy bees by the form of the female hind leg, which is modified to form a corbicula; 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. The blood or hemolymph, as in other arthropods, is carried in an open circulatory system. The body organs, “heart” (dorsal aorta), muscles, etc. are surrounded in a reservoir of blood. The dorsal aorta does pulse blood through its long tube, though, so there is a circulation of sorts.
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 container called the spermatheca. This is where the queen stores sperm from her mating. Before she lays the egg, she will decide whether to use sperm from the spermatheca to fertilise it or not. Non-fertilised eggs grow into males, and only fertilised eggs grow into females and queens.
As in all animals, hormones play a big role in the growth and development of the bumblebee. The hormones that stimulate the development of the ovaries are suppressed in the other female worker bees while the queen remains dominant. Salivary glands in the head secrete saliva which is mixed with the nectar and pollen. Saliva is also mixed into the nest materials to soften them. The fat body 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.
Like all bee tongues, the bumblebee tongue (the proboscis) is composed of many different mouthparts acting as a unit, specialised to suck up nectar via capillary action. When at rest or flying, the proboscis is kept folded under the head. The abdomen is divided into dorsal tergites and ventral sternites. Wax is secreted from glands on the sternites.
The brightly-coloured pile of the bumble bee 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.
A bumblebee does not have ears, and it is not known whether, or how, a bumblebee could hear sound waves passing through the air; however, they can feel the vibrations of sounds through wood and other materials.
Habitat
Bumblebees form colonies. These 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. Bumblebee nests may be found within tunnels in the ground made by other animals, or in tussock grass. Bumblebees sometimes construct a wax canopy over the top of their nest for protection and insulation.
In temperate zone species, in the autumn, young queens mate with males (drones). The bumblebee eggs that hatch develop into female workers, and in time the queen populates the colony, with workers feeding the young and performing other duties similar to honey bee workers. New reproductives are produced early in the year and the queen and workers die, as do the males.
Queen and worker bumblebees can sting, but unlike a honey bee’s, a bumblebee’s stinger lacks barbs — so they can sting more than once. Bumblebee species are normally non-aggressive, but will sting in defense of their nest, or if harmed. Female cuckoo bumblebees will aggressively attack host colony members, and sting the host queen, but will ignore other animals (including humans) unless disturbed.
(Source: Wikipedia – The free online encyclopedia.)

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