Margaret Thomas NDB
Scientific Beekeeping
Scientific Beekeeping
We humans and all mammals have our skeletons inside our body holding us up and protecting our vital organs. That is excepting the brain which is encased in a bony container. Growth occurs at the ends of the bones allowing us to grow from tiny baby size to plus 6 foot.

Bees, on the other hand, being insects have their skeletons on the outside, termed an exoskeleton. This harder layer, called a cuticle, cannot expand to allow for growth so the insect has to shed its cuticle and re-grow another larger one. With insects including bees this growth only happens in the larval stage. The adult bee cannot change its size, though expansion and contraction of the abdomen does occur during 'breathing'.

The cuticle is made up of various layers. The innermost basement membrane anchors the epidermal cells. These are living cells and one of their function is to grow the layers above. The next outer layer is the endocuticle which is tough but flexible. The exocuticle is the next layer and this is made up of chitin and, in the adult insect the chitin is tanned to form sclerotin making this layer hard. The outermost epicuticle layer is a thin layer of sclerotin topped by a waxy coating. It is this layer of wax that makes the insect waterproof, and conversely means we can kill insects with dilute washing up liquid. This would dissolve the wax and allow water into the body and body fluid to leak out. The structure of the cuticle is involved in the colour variation of insects.

To allow growth the old cuticle needs to be shed. In fact in the bee most of the nutrients are reabsorbed and not junked. Various hormones play a part in shedding the cuticle. Juvenile hormone falls and ecdysone rises. Inactive moulting fluid is secreted into a gap between the epidermal cells and the endocuticle. An ecdysal membrane now forms above the epidermal cells to prevent damage to these cells. Moulting fluid is activated to 'digest' and reabsorb nutrients from the old cuticle. The epidermal cells multiply and a new larger cuticle is formed under the safety membrane. The new cuticle expands and the layers become differentiated.

Why is this relevant to us beekeepers? Well the Sacbrood virus prevents reabsorption of the old layers and the larva dies, drowning in its own fluids.

The cuticle is a continuous layer of varying thickness and in the adult forming solid plates separated by thinner flexible membranes to allow for movement, ie allowing expansion and contraction in the abdomen to aid air intake and expulsion.

To use technical terms the top or dorsum of the insect is called the tergum, the bottom or ventral the sternum. The plates on the side are the pleuron.

Bees breathe through a complex structure of network of tracheae and air sacs. Oxygen is sucked into the body through the spiracles by the expansion of the air sacs, then the spiracles are closed and air sacs are compressed to force the air into smaller tracheas, which become smaller and smaller until individual tubules reach individual cells. Carbon dioxide is expelled through these same tracheae. Other organs such as the many sense organs frequently arise from the cuticle.

Margaret Thomas NDB

This information is based on an article that appeared in the Scottish Beekeeper Magazine in February 2017