wing beats, wing condition and age, when a bumblebee can and cannot fly, warming up the flight muscles, flight speed, weight, distances flown
Bumblebees have four wings, the two rear
wings are small and usually attached to the front wings by a row of hooks called
hamuli or hammulae (see the diagram on the right and photographs below) which catch on to ridge on the lower margin of
the front wing. This is why many people think bumblebees have only two wings.
The front and rear wings can be clearly seen in the photographs further down the page.
Bumblebee wings are formed of the same material as the rest of the exoskeleton - chitin.
am often asked about the number of times the wing beats per second. I have
never measured this, but have seen figures of 130-240 quoted. This is nothing
when compared to the 1046 beats per second of a
midge. The wings are powered by the flight muscles which take up almost the whole volume of the thorax.
When a bumblebee can and cannot fly
I'm often asked about the story that bumblebees shouldn't be able to
fly but can. Well there is a link on my FAQ page to an full explanation of the
story, and a wonderful
BBC short video, but the gist of it was that the engineers involved were using figures
and equations as applied to fixed-wing aircraft, but the bumblebee wing is not
fixed, it can flap and swivel. So it would have been more accurate to use the aerodynamics that are applied to helicopters. However a bumblebee cannot fly if its wing muscle temperature falls below 30oC. In flight
the muscle temperature is regulated to stay between 30 - 44oC. And all this is powered by the sugars found in the nectar the bees suck from flowers.
Bumblebee flight speed is 3.0 - 4.5 metres per second. This is 10.8 - 16.2 kilometres per hour, or 6.7 - 10.7 miles per hour. Compare this with other insects.
Bumblebees are what are called
"central place foragers" the central place being the nest. They fly out to the
source of nectar/pollen then fly back. Bombus
pratorum tends to forage fairly close to the nest, while others, Bombus terrestris, lucorum and lapidarius, will often ignore or desert apparently
"good" foraging sites to travel great distances to other sites. The distance a
bumblebee is willing to travel to gather food obviously has great implications
when considering sites for the planting of genetically modified plants with
non-sterile pollen. Studies on distances flown by bumblebees show that the
foraging range varies considerably according to species and food availability,
but most workers tend to stay within 5 km of the nest. However distances as
large as 20 km have been recorded.
In spring masses of bumblebee queens have been seen flying the 80 km over the Gulf of Finland between Finland and Estonia. Reasons for the exodus are not yet known, but could be due to competition for nest sites, or fleeing from one of their major predators in the area - the vole - whose population cycles build to huge numbers in some years, then crash before building again.
condition and age.
of the wings can be used to age a bumblebee to some extent. Look at the
bumblebees on the left and right, notice that in the photograph on the left the edge of her wing is damaged. This is
typical of an older bee. It doesn't seem to hinder their ability to work. Many
bumblebees I have examined that have had ragged wings have also had bald patch
on the thorax (though this is very rare in Bombus pascuorum), and in sunny
summers their hairs have faded in colour. I think this is a Bombus humilis worker, but as I didn't capture
her I cannot be sure. Both were photographed in the centre of Paris, just outside
my study window. In the left pollen basket is partially full, and she, and her nest
mates returned to the pot of flowers regularly. The wings above were taken from a dead queen I found in Scotland. She appeared in good condition, and there was little wing damage, so I am not sure what killed her.
Warming up the flight muscles
At rest a bumblebee's body temperature will fall to that of its surroundings. To raise the temperature of the flight muscles high enough to enable flight the bumblebee shivers, rather the same a we do when we are cold. This can easily be seen in a grounded bee as her abdomen will pump to ventilate the flight muscles. The rate of pumping can give an indication of the temperature of the bee. Ranging from around 1 pump per second when she is at 10oC, to 6 pumps per second when she reaches 35oC. The time taken to raise the thorax temperature has been studied and is laid out in the table on the right. There is an excellent BBC video showing this.
When food is plentiful and outside temperatures fall below 10oC bumblebees generally stay inside the nest and live off their stores. At times when food is scarce or stores are low they will forage when the outside temperature is as low as 6oC, and queens will forage at even lower temperatures. In severe conditions they have even been known to vary their flying height to and from the nest to take advantage of any temperature differences.
||(C) 1997 - 2013
||Sure, marriage can be fun some of the time. Trouble is you are married all of the time. - Maxine
|Bee/air temp. oC
||Time taken to reach 30oC
||a few seconds
|| 5 minutes
Bumblebee workers can weigh from 0.04 g to
0.60 g, and some large queens can reach 0.85g. Bombus lucorum workers range from 0.04 - 0.32 g and the queens from 0.46 - 0.70 g; B. terrestris workers range from 0.05 g - 0.40 g. Some of the early workers of
smaller species are really tiny, and no bigger than houseflies. In other
species, or nests where food has been plentiful the workers can be almost the
same weight as the queen. In addition to body weight, female and queen
bumblebees can carry as much as their whole weight again in pollen in their pollen baskets, and nectar/honey in