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Authors: Dave Goulson
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metabolic rates, but a bumblebeeâs is roughly 75 per cent higher.
This simple fact explains an awful lot about the biology and conservation of bumblebees. They have to eat almost continually to keep warm; a bumblebee with a full stomach is only ever about forty minutes from starvation. If a bumblebee runs out of energy, she cannot fly, and if she cannot fly, she cannot get to flowers to get more food, so she is doomed â unless a small boy comes along and gives her a teaspoon of honey. With a stomach full of sugar she can start to fire up her flight muscles, shivering them to produce heat, and once she gets up to about 30°C, off she goes â¦
A bumblebeeâs dense furry coat has obvious advantages, but it can create problems when the weather is warm. Bumblebees cannot help but produce lots of heat when they fly, which can be difficult to get rid of if the air temperature is also high. This is probably why bumblebees are not common in Mediterranean countries, and why there are almost none in the tropics. If their body temperature exceeds 44°C they will die; as they approach this lethal limit their metabolism collapses and they become unable to fly. It is noticeable that those species of bumblebee that occur in warmer climates tend to have shorter fur, while those from high latitudes and altitudes tend to be very large and very furry. Hence the huge size and long shaggy coat of the worldâs largest bumblebee, Bombus dahlbomii , which inhabits the high Andes of South America.
Bumblebees do have a trick to help them lose heat in hot weather. As already mentioned, they normally keep their abdomen at a much lower temperature than their thorax, with the narrow waist connecting the two acting as a barrier. If the thorax starts to get too hot, the abdomen starts rhythmically to contract, sending surges of cool blood into the thorax and sucking back waves of hot blood. This heats the abdomen and so raises the surface area from which heat can be lost. Nonetheless, on very hot days in summer bumblebees will tend to stop foraging as noon approaches and recommence in the cool of evening.
Pumping heat from the thorax to the abdomen can also serve a very different purpose. The northernmost social insect in the world is a bumblebee known as Bombus polaris , which lives well within the Arctic Circle: large and unusually hairy, it can exist in regions where, even in the height of summer, air temperatures rarely exceed 5°C. Unlike other bumblebees, the Bombus polaris queens maintain a stable, high abdominal temperature (greater than 30°C) by pumping hot blood from their thorax to the abdomen. This enables them to develop eggs within their ovaries quickly, which is important in the very short Arctic summer. As the workers and males have no eggs to develop, their abdomens are substantially cooler.
The larger the bee, the easier it is for it to keep warm but the more prone it is to overheating in hot weather. This may explain why queen bees are so much larger than workers, for they are on the wing earlier, in the spring when the weather is cold. It may also explain why the worker bees that leave the nest to gather food tend to be larger, on average, than those that stay in the nest to look after the brood.
Moreover, bumblebees manage not only their own body temperatures, but also those of their brood and the nest. Dependent upon species, bumblebees have anywhere between two and seven months to complete their annual cycle. This would not be possible unless they speeded up the development of their offspring by keeping them warm, and as the grubs are flabby near-immobile creatures with very small muscles, they cannot warm themselves. Instead they are incubated by the queen (if they are the first batch of offspring), or by the workers. Once there are enough of them, the combined heat emanating from the workforce keeps the whole nest at a cosy 30°C or so without much difficulty. As with individual bees,
This simple fact explains an awful lot about the biology and conservation of bumblebees. They have to eat almost continually to keep warm; a bumblebee with a full stomach is only ever about forty minutes from starvation. If a bumblebee runs out of energy, she cannot fly, and if she cannot fly, she cannot get to flowers to get more food, so she is doomed â unless a small boy comes along and gives her a teaspoon of honey. With a stomach full of sugar she can start to fire up her flight muscles, shivering them to produce heat, and once she gets up to about 30°C, off she goes â¦
A bumblebeeâs dense furry coat has obvious advantages, but it can create problems when the weather is warm. Bumblebees cannot help but produce lots of heat when they fly, which can be difficult to get rid of if the air temperature is also high. This is probably why bumblebees are not common in Mediterranean countries, and why there are almost none in the tropics. If their body temperature exceeds 44°C they will die; as they approach this lethal limit their metabolism collapses and they become unable to fly. It is noticeable that those species of bumblebee that occur in warmer climates tend to have shorter fur, while those from high latitudes and altitudes tend to be very large and very furry. Hence the huge size and long shaggy coat of the worldâs largest bumblebee, Bombus dahlbomii , which inhabits the high Andes of South America.
Bumblebees do have a trick to help them lose heat in hot weather. As already mentioned, they normally keep their abdomen at a much lower temperature than their thorax, with the narrow waist connecting the two acting as a barrier. If the thorax starts to get too hot, the abdomen starts rhythmically to contract, sending surges of cool blood into the thorax and sucking back waves of hot blood. This heats the abdomen and so raises the surface area from which heat can be lost. Nonetheless, on very hot days in summer bumblebees will tend to stop foraging as noon approaches and recommence in the cool of evening.
Pumping heat from the thorax to the abdomen can also serve a very different purpose. The northernmost social insect in the world is a bumblebee known as Bombus polaris , which lives well within the Arctic Circle: large and unusually hairy, it can exist in regions where, even in the height of summer, air temperatures rarely exceed 5°C. Unlike other bumblebees, the Bombus polaris queens maintain a stable, high abdominal temperature (greater than 30°C) by pumping hot blood from their thorax to the abdomen. This enables them to develop eggs within their ovaries quickly, which is important in the very short Arctic summer. As the workers and males have no eggs to develop, their abdomens are substantially cooler.
The larger the bee, the easier it is for it to keep warm but the more prone it is to overheating in hot weather. This may explain why queen bees are so much larger than workers, for they are on the wing earlier, in the spring when the weather is cold. It may also explain why the worker bees that leave the nest to gather food tend to be larger, on average, than those that stay in the nest to look after the brood.
Moreover, bumblebees manage not only their own body temperatures, but also those of their brood and the nest. Dependent upon species, bumblebees have anywhere between two and seven months to complete their annual cycle. This would not be possible unless they speeded up the development of their offspring by keeping them warm, and as the grubs are flabby near-immobile creatures with very small muscles, they cannot warm themselves. Instead they are incubated by the queen (if they are the first batch of offspring), or by the workers. Once there are enough of them, the combined heat emanating from the workforce keeps the whole nest at a cosy 30°C or so without much difficulty. As with individual bees,
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