The physiology of gas exchange between bees and their environment
Breathing in insects is very different from the typical lung system used in mammals, who are able to use a circulatory system to bring atmospheric oxygen to the cells using blood cells. Insects rely heavily on the use of diffusion in order to perform gas exchange, where they can route the flow of atmospheric air directly to their cells to be diffused across the cell membrane. The system insects employ to achieve this are called tracheae which are a vast network of branches that can reach all the tissues in the head, abdomen, and thorax of an insect from the outside surface of their bodies to the innermost cavities. The tracheae can be viewed as vein-like networks that deliver air to each of the cells, but they do not contain body fluids of any kind, only air from the outside. The air from outside can enter these tubes through pores on the external part of their bodies called spiracles [2]. The number of spiracles varies from insect to insect but bees have 10 spiracles arranged in bilateral pairs on each side of their bodies. [3]
As the air travels further from the spiracles, the walls of the tracheae become smaller in diameter and are considered to be tracheoles (in a similar way to bronchioles in lungs are formed). Tracheoles are small tubes that form the terminal ends of tracheae. The largest part of the tracheoles are 1 µm wide in diameter and the smallest parts are 0.02 µm - 0.2 µm wide in diameter [2]. These tracheoles are small enough to run in between the cells to deliver oxygen and the arrangement of them depends on the metabolic needs of the individual insect.
In slightly larger insects, including bees, additional ventilation methods are available to pull oxygen into the body and release carbon dioxide back outside called conspicuous ventilation. As seen in the video below, bees are able to compress and expand their abdomen to create a negative or positive pressure differential in the air, causing the air to be sucked in or forced out of the spiracles. Another way to create additional ventilation is flight driven,called autoventilation. This gives the flight muscles more air flow, which in turn allows for extended flight times [2].
Additional Resources
Domenis, L. (2017). Tracheoles (respiratory tubes) of Apis mellifera (bee). Small World Nikon. Retrieved October 25, 2020, from https://www.nikonsmallworld.com/galleries/2017-photomicrography-competition/tracheoles-respiratory-tubes-of-apis-mellifera-bee
Hill, R. W., Wyse, G. A., & Anderson, M. (2016). Animal Physiology (4th ed.). Sinauer Associates, Inc. Publishers.
https://images.app.goo.gl/tCC8qTiUeR68CR7P9