Bumble Bees: Social Life & Thermoregulation.

Common carder (Bombus pasquorum) queen bumble bee taking advantage of warm weather and hawkweed on Wednesday.

Despite a fair bit of rain over the last week it’s been warm with lots of bee activity. It’s hard to believe that the Himalayan balsam is still flowering by the river Nairn. But it is and the bees are still coming home coloured silvery white! The ivy is in full bloom near Connie’s garden and she reports it full of honey bees and others. This is a good time to check ivy for Asian hornet incursions since the glucose-packed nectar is highly attractive to this potentially threatening insect.

Connie and I spent Tuesday after school counting varroa, scraping propolis off dummy boards and blow torching woodwork. The colony treated with Apilife Var responded well. The bees did a good job of chewing up and clearing away the fragile strips and spreading the ingredients around the hive with a good varroa kill. Fortunately it has been warm enough for it to work well.

My go to methods of alleviating the pain from stings.

Connie got her first sting on Tuesday when a bee got stuck on her leggings. She coped really well but it was was very sore initially. Things quickly improved after an application of Bai Hua You (bottle on the right). A friend who keeps bees in China gave me some a few years ago and it does help with the pain. You can see I’ve used it a bit! It’s what the Chinese beekeepers always keep in their tool kit. It certainly masks the alarm pheromone, as does Tiger Balm which has the same effect. Connie cheered up when I told her that she was a real beekeeper now as all beekeepers get stung from time to time.

Bumble Bees.

Gelda MacGregor’s zoom presentation for the local beekeeping association on bumble bees was very interesting and got me thinking again about thermoregulation and how it is that bumble bees can fly at incredibly low temperatures.

Did you know that there are 250 species of bee in the UK? These comprise 24 species of bumble bees, one honey bee and 225 solitary bees. Solitary bees have no worker caste to raise offspring and only drones and queen are produced. The queen gets mated, overwinters, finds a nesting place in spring and lays eggs. She leaves provisions for the larvae before heading out and leaving them to get on with it. The solitary queen works alone though her nest may be very close to others of the same species. They may even share an entrance.

Bumble bees are social insects because, like the honey bee, they have 2 castes of female; queen and worker and there are separate jobs to do once the spring nest is established. The mated queen overwinters in a sheltered place whilst the drones and workers die off. In spring the queen appears on early plants like willow. She needs to build her own reserves for egg laying so she collects pollen. She also needs a store of nectar for herself so she arranges little pots of honey in waxen cells around her nest. She works alone initially but soon the new worker bumble bees emerge and take on the foraging roles leaving the queen to lay and incubate eggs. The amazing thing about bumble bees is that the queen actually sits on the eggs like a broody hen and transfers heat from her abdomen by conduction to the eggs. I’ll tell you how she is able to keep her abdomen warm enough in a moment.

Bumble bee queens usually mate with only one drone, but some species mate with 2, unlike polygamous honey bee queens whose average number of mates is 7-17. Bumble bee sex takes place on the ground and not in the air like the honey bee. It can last a long time, up to several hours. The reason for this is that the drone produces a sticky substance which seals the queen’s vagina so she cannot mate with another, thus preserving and perpetuating his genes. Unlike the honey bee drone, he lives to see another day, and another mating.

Bumble Bee or Bumblebee?

I use two words because I’m following the entomology rule for insect common names. This rule states that if the insect is what the name implies you write two words. So, it’s ok to write blow fly or house fly because they are true flies from the diptera order. However, the same is not true for butterflies because they are are not flies therefore the names are run together.

Heat Regulation.

Bumble bees originated in the northern hemisphere and are able to fly in the arctic. We hear them working long into some very cool spring evenings here in Nairnshire which is almost on the same latitude as Moscow. How is this possible you may wonder? Well they are very hairy insects with a thick covering of feather-like plumose hairs that trap heat. Like honey bees they can isometrically contract wing muscles to generate heat for which they also require the energy from nectar. But that’s not the full story.

Although the internal organs are pretty similar in honey bees and bumble bees, heat transfer is different. Because bumble bees are larger and hairier, less heat is lost by convection when flying. However, the main difference is in the construction of the circulatory system.

Both have open circulatory systems with long hearts with valves preventing backflow. So, haemolymph (they do not have red blood) is pushed forward to the head. The returning haemolymph sloshes around the body and returns to the heart via the abdomen where it picks up nutrients and gets rid of waste via the equivalent of our kidneys called Malpighian tubules.

Both insects require a thoracic temperature of 35 degrees Celsius to warm the flight muscles but bumble bees can easily overheat because they generate much more heat in their flight muscles than do smaller insects. If you look at the honey bee aorta in my drawing, you will see that as the aorta enters the thorax through the petiole, or waist, it takes on a convoluted cork screw appearance. This is where the aorta becomes a heat exchanger and helps the cold haemolymph moving forwards to the thorax to extract some heat from the hot haemolymph moving rear-wards. This convoluted heat exchanger is situated where it is, as it enters the thorax, so that the rear-wards moving haemolymph gives up heat just before leaving the thorax thus keeping the honey bee thorax warm enough to support flight.

Renowned entomologist and author Bernd Heinrich studied insect thermoregulation in the 1970’s, and we owe our present knowledge to him. Heinrich likens the bumble bee to a Lincoln Continental car that is so big it needs a cooling system of circulating fluid to disperse heat from the motor via a radiator. The honey bee is like the Volkswagon Beetle; much smaller and can be air cooled without any special mechanisms.

Bumble bees need to have a warmer thorax at certain times such as during flight, and at other times a they need a warmer abdomen for incubating eggs. But how is this achievable? If you look at the bumble bee heart and aorta you will notice that it makes a large loop under an insulating air sac (honey bees have these sacs too but I didn’t want to spend too long drawing all the parts in yesterday). These air sacs can insulate the thorax from losing heat to the abdomen. The loop brings cool haemolymph entering the thorax close to the warm haemolymph leaving the thorax having been heated by respiratory muscles. Heat exchange, with heat transferring from a warmer area to a cooler one, is possible with this system because only a few layers of cells separates the two channels. This is called a counter current system. Some vertebrates like seals employ this mechanism enabling them to swim by directing heat to their flippers in icy conditions.

If bumble bees didn’t have this counter current system, heat loss from the thorax would be much greater and there wouldn’t be a continuous flow of haemolymph to carry nutrients for fuelling the muscles. The muscles would easily cool causing problems during foraging. The average length of foraging trips is 1/2- 1.5 hours and, like honey bees, they can cover a three-mile radius which works out as a staggering 28.26 square miles. (3 miles squared =9 x π (Pi 3.14) =28.6 miles).


That’s heat conservation covered, but what about the long foraging trip on a hot day? Bumble bees are prone to overheating but amazingly they can bypass the counter current system and have cool haemolymph going up to the thorax with the warm coming back to abdomen alternately rather than simultaneously. With this situation there is no heat exchange through the cell walls and heat from the thorax is dumped in the abdomen. It is thought that the front part of the ventral diaphragm acts like an alternating switch allowing flow of haemolymph through the same channel but not at the same time.

Wagging Tongues.

You’ve probably seen film of kangaroos licking the insides of their front legs and lying in the shade with those parts exposed trying to cool a bit by evaporative heat loss? Well, bumble bees have a similar strategy of evaporative heat loss. They can lose 2-3 degrees C in flight by regurgitating nectar and holding it on the ends of their tongues which they wag about in the breeze.

Bumble bee defecating in flight. Photo by Mark Parrot.

More Information

For more info on bumble bees contact https://www.bumblebeeconservation.org/


Heinrich, B,. 1979, Bumblebee Economics, Harvard University Press, Cambridge.

13 thoughts on “Bumble Bees: Social Life & Thermoregulation.”

  1. Well that was very interesting! Thank you, Ann. I had read about temperature control (and “Gobbetting” on page 155) in Chapter 7 ‘Flight’, of Lesley Goodman’s ‘Form and Function of the Honey Bee, but to have the diagrams and comparison with bumble bees was fascinating. You explained it beautifully and made it easy and a pleasure to read.

    1. Thank you Margaret Anne, I’m glad that you enjoyed reading it. Goodman’s book is pretty amazing really. Along with Stell, Dade, Snodgrass, and Winston I it use for exam revision.

      1. Yes, it was sad that Lesley Goodman died before finishing her amazing book. i like all the others too, except Winston.

        1. Can you suggest another biology book, Margaret Anne? Winston is 30 years old and covers mostly bee behaviour rather than anatomy and physiology. I found it useful though and it is the first book that I have written in–lots of things in pencil to help me in the future, like labelling diagrams.

          1. Ann, Celia Davis’s books ‘The Honey Bee Inside Out’ and The Honey Bee Around and About’ filled a huge gap, then I went on to read scientific papers, and found myself thinking quite often “Celia has read this.” As you know I like Clarence Colinson’s ‘A Closer Look at Bee Biology’ 🙂 and ofcourse everything written by Tom Seeley. Another important book is ‘Mating Biology of Honey Bees’ by the Koenigers, Jamie Ellis and Lawrence Connor; these authors (like Tom Seeley) were very quick in answering any further questiions I had. Susan Colby, is brilliant as she knows everything there is to know about the functioning of queens. She told me that queens do not go ‘stale’ they merely reach a stage in their development where the start laying and no longer attempt to mate; but they can still be successfully instrumentally inseminated after they have started laying, then go on to fertilise eggs eggs. As you say printed books eventually need to be updated but we are lucky to be around now, when we can read papers online even if we can somtimes only access an abstract. If I think of anything else, I will get back to you xx

          2. Thanks, Margaret Anne that is really interesting about queens. I’ll take a look at some of the ones you mention–I already have a couple of them.

          3. I should have also mentioned an important work ‘Insect Physiology’ Hardcover – 8 Aug. 2015
            by Vincent B. Wigglesworth (Author). I found the detail in the section on the exoskeleton to be really satisfying.

      2. I should have also mentioned ‘Insect Physiology’ by V M Wigglesworth. described as; “This work has been selected by scholars as being culturally important, and is part of the knowledge base of civilization as we know it”. The section on the structure of the exosleleton is fascinating.

  2. I was sorry to miss Gelda’s presentation. Better luck next time.

    A very interesting blog, Ann. We share an interest in spelling and the correct use of words, so I liked the piece about insect names, and bumble bees are interesting in being so similar, and yet so different from “our” little wonders.

    Connie was very brave and recovered quickly from her (first!) painful experience in beekeeping.

    We are actually about 90 nautical miles north of Moscow’s most northerly international airport (Sheremetyevo). The main reason for the more extreme temperatures in Moscow (both summer and winter) is due to it being fairly central in a large land mass. Land surfaces tend to heat and cool much more than large expanses of water, which we are much closer to. Plus, we, of course, have the famous Gulf Stream – lucky us!

  3. Regarding the temperature differences in Moscow and Inverness, I can say from personal experience that minus 25 degrees C in Moscow, but in the normal dry, nil wind conditions, feels very much more comfortable than minus 1 degree in horizontal slicing rain in 40 knots of wind in Stornoway! The vodka helps, of course…

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.