Bumblebee Heat Regulation

While flying,bumblebees have a body temperature that is generally well above that of the air around them,and tends to be constant at about 35 C.Keeping warm is harder the smaller you are. Small creatures,like bees,have a vast surface area relative to their volume,and lose heat incredibly quickly.Yet bumblebees can keep themselves warm even when the surrounding air is 30C cooler than their body temperature.Scientist Bernd Heinrich found that the answer to bees’ability to retain heat is in two parts:keeping heat in, and generating it in the first place.Keeping warm is helped if you have insulation,and of course bumblebees have furry coats.The vital thing for a bumblebee is to keep its thorax (the middle section)warm, because this is where the flight muscles are;unless the thorax is warm enough,the muscles cannot contract sufficiently fast,and the bee cannot take off.The temperature of the abdomen does not matter much in flight.The abdomen and thorax in a bumblebee are connected by a very narrow waist,and the front part of the abdomen contains a sac of air,so heat loss from the thorax to the abdomen is minimal (air is a poor conductor).A bumblebee’s heat is generated by the contractions of the flight muscles.In flight a bumblebee flaps its wings 200 times per second.This generates a lot of heat,but of course comes at a cost:bumblebee flight is enormously expensive in terms of the energy that it uses.Consequently,bumblebees have to eat almost continually to keep warm.

A bumblebee’s 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.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 world’s 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. 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 seeking food as noon approaches and recommence in the cool of the 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 5C. 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 begin flying 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.?

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?While flying,bumblebees have a body temperature that is generally well above that of the air around them,and tends to be constant at about 35 C.Keeping warm is harder the smaller you are. Small creatures,like bees,have a vast surface area relative to their volume,and lose heat incredibly quickly.Yet bumblebees can keep themselves warm even when the surrounding air is 30C cooler than their body temperature.Scientist Bernd Heinrich found that the answer to bees’ability to retain heat is in two parts:keeping heat in, and generating it in the first place.Keeping warm is helped if you have insulation,and of course bumblebees have furry coats.The vital thing for a bumblebee is to keep its thorax (the middle section)warm, because this is where the flight muscles are;unless the thorax is warm enough,the muscles cannot contract sufficiently fast,and the bee cannot take off.The temperature of the abdomen does not matter much in flight.The abdomen and thorax in a bumblebee are connected by a very narrow waist,and the front part of the abdomen contains a sac of air,so heat loss from the thorax to the abdomen is minimal (air is a poor conductor).A bumblebee’s heat is generated by the contractions of the flight muscles.In flight a bumblebee flaps its wings 200 times per second.This generates a lot of heat,but of course comes at a cost:bumblebee flight is enormously expensive in terms of the energy that it uses.Consequently,bumblebees have to eat almost continually to keep warm.

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