While it is still too cool for many bees, the first bumblebees are already cavorting on the flowers. In general, insects have been underestimated for far too long
The first bumblebees are already on their way. And this despite the fact that honey bees are considered to be particularly hard-working. But while honey bees only really wake up at outside temperatures of around 10 degrees Celsius, bumblebees are quite active at 6 degrees Celsius, and the queens sometimes even around freezing point. The workers can be on the go for an amazing 18 hours a day if they start right after sunrise and only come to rest in the hive late in the evening – they have then visited up to 1000 flowers.
How do the animals do it? In fact, the bumblebee has many a trick up its sleeve to accomplish these feats. First, there is its bulk, which allows it to store much more heat than a small honey bee. The larger body offers more space for muscle groups and therefore also for excellent thermoregulation.
Bumblebees can detach their four wings from their muscles and then contract and relax them about 200 times a second without even moving their wings. Biologists speak of “heat tremors” because these muscle contractions generate heat that heats up the entire body and – to a certain extent when it is idling – brings it to flight temperature. This is important because bumblebees need a muscle temperature of 30 degrees Celsius to fly. On the other hand, they also overheat quickly and have to cool down first when the muscle temperature reaches 44 degrees Celsius at the latest. They can fly out in bad weather, but have to stay in the shade on hot days or find some other way to cool themselves. Even if it cannot shed its thick fur, which can be quite annoying in summer, the bumblebee can give off excess heat to the environment via its lower abdomen. The warm bottom has another advantage: she can use it to incubate her offspring, which is normal for birds but rather unusual for insects.
Sunbathing invigorates
Sunbathing also helps the animals to regulate their body temperature. In a laboratory experiment with artificially heated flowers, Lars Chittka and his team from Queen Mary University in London were able to prove that a higher temperature of just 4 degrees Celsius is enough to attract the majority of animals to sunbathe. If the temperature advantage increased even more, more bumblebees took a seat on the warmer flower. If the difference was a full 10 degrees Celsius, on average almost two-thirds of all individuals ended up on the higher-temperature alternative. Chittka sums up his study, which was published in the journal Biologist: “The results show that the flowers offer pollinators the heat as a reward, in addition to food.”
Some plants have specifically adapted to this need for warmth. Thanks to special surface structures and dark flowers, they heat up faster in the morning than others. A team from Canada’s University of Guelph has shown that some flowers focus the sun’s energy like satellite dishes, allowing temperatures at their center to be up to 10 degrees Celsius above ambient.
Other plants, such as the bumblebee, have adapted to the weight of the big bumblebee: the lower part of the flower, divided into two, offers a kind of stable runway for the approaching bumblebee. Due to their size, the animals can also transport significantly more nectar and pollen than honey bees. Their greater strength also allows them to penetrate deep into those flowers that remain closed to the weaker bees. No wonder, then, that bumblebees are becoming increasingly popular in commercial crop cultivation due to their excellent pollination performance.
Good-natured pollinator
In addition, the Brummer are extremely good-natured, which is ideal for pollination in greenhouses. However, it is a misconception that bumblebees cannot sting. Although they don’t feel like doing it very much and only do it reluctantly when they feel threatened, they can do it very well. First, however, there is usually a threat by stretching out a leg to defend the attacker. If he doesn’t understand this hint, they lie down on their backs and present their clearly visible sting on their abdomen, which is often accompanied by a loud growl. If you still don’t let go of Hummel, you can definitely catch a sting.
Incidentally, a bumblebee cannot sting simply by sitting on the hand because its stinging muscles are too weak. To do this, it must either support itself with its back or hit so hard on approach that the stinger can penetrate human skin. But who wants that? Certainly not the bumblebee.
