The Bee Space
Honey bees are efficient builders. They don't like wasted space in their hive, and have come up with ideal ways to make the most of the space they have. Honey bees, of course, build beeswax honey combs inside of a hollow cavity that we call their hive -- whether it's an artificially crafted box provided by humans or a hollow tree or other appropriate space.
When bees first move into a new home, they must start construction right away. Without beeswax combs, they cannot store any honey, and the queen bee will have no place to lay eggs and produce the next generation of hard working busy bees. Beekeepers provide wooden frames and foundation (sheets of beeswax or wax-covered plastic) imprinted with a honeycomb pattern, which the bees recognize and use as a pattern to begin comb construction. This foundation encourages honey bees to build flat, even, parallel honey combs in the centers of the wooden frames, making it easy to remove them from a hive for inspection, or to harvest honey. Without these guides, honey bees will still build vertical combs, but they will often be of varying lengths, and will curve around each other according to the bees' whim.
A hollow tree may have a narrow, round cavity, but it may extend vertically for quite a distance. Over time a colony of bees will eventually fill their hive with combs. Comb building begins at the top of the cavity, with the comb hanging straight down, even though it may follow a curbed path horizontally. This is because, over time, the comb can grow quite long and can become quite heavy when full of honey. If it were to be built at any angle, it would eventually break off under it's own weight.
How big is a bee space?
When bees are ready to begin constructing a second comb, it will run parallel to the surface of the first. Combs are always just about an inch thick, sometimes slightly thicker at the top, where honey is stored, but usually very uniform lower down in the brood area. Neighboring combs are always separated by a small gap. This gap is a fairly uniform, but can range from 1/4" to 3/8" (6 mm to 9 mm). Essentially this bee space is just the right amount of room for two bees to work or pass each other, back to back, on opposite combs, without getting in each other's ways.
Any space in a bee hive that is larger than a bee space -- larger than 3/8" -- will eventually filled with comb for incubating bee brood or storing food (pollen or honey). But any space smaller than 1/4" is unusable for honey bees. It's too small to build a usable cell, and potentially gives pesky hive invaders, such as ants or small beetles, places to hide. The bees respond by sealing up these smaller gaps.
Sticky situation
Honey bees gather saps and resins from trees, which are produced at their tips where new growth is budding out. These resins contain numerous compounds that make them naturally resistant to bacteria, viruses and fungal infections. They are a source of natural antibiotics! Honey bees gather these resins and bring them back to the hive, mix them with beeswax and salivary secretions, to become a material known as propolis.
Honey bees coat the entire inner surface of a hive cavity in this germ-killing wonder-product, effectively sealing up and strengthening rotting wood, and "caulking" small cracks and crevices in the hive wall to seal out drafts. The process also provides a waterproof layer to the inner surface of their home, and makes it smoother to walk across. And as the bees enter their hive and walk across the inner walls, the antimicrobial propolis surface helps to sterilize their feet after being outside the hive. Propolis is an important part of the bee colony's social immune system that helps keep the whole colony healthy. Propolis is also added to beeswax combs over time to strengthen them and help keep them clean and ready for the queen to lay eggs in sterilized cells.
Beekeepers have long known about propolis and its medicinal properties. It has been used as an antiseptic and anti-inflammatory cure since ancient times. Egyptians used it in the embalming process and Roman soldiers supposedly carried a blob of propolis into battle for treating wounds after battle. Of course, the bees were using it long before that. And beekeepers have long called it "bee glue" because of the way it tends to stick together everything inside a bee hive. But a hive with excessive propolis use is probably violating the bee space.
The concept of the bee space is what makes modern beekeeping possible. In ancient times bees were kept in terracotta pots, hollow logs, or straw baskets called skeps. The bees were allowed to build their combs as they pleased, until one day they were smoked out, and all of their honey combs were scooped out and taken away. These were crushed and strained to remove the honey, after which the wax was melted down to make candles or used for other industrious crafts. If the bees survived, they had to begin building their homes all over again.
The basis of modern beekeeping
Modern bee hives, called Langstroth hives, are modular and full of wooden frames to make it easier to take them apart and put them back together with the least disturbance to the bees. These hives are designed with the bee space in mind. If a hive is built with 3/8" in between all the wooden parts, then the bees generally agree there is just the right amount of space between frames and boxes, and won't' fill in these gaps with propolis. Also, when they build their combs onto the provided foundation in the frames, each comb runs parallel to each other, with exactly one bee space between finished combs. Thus the frames are easy to remove and easy to replace without harm to the combs or bees. If a careless beekeeper leaves out a frame or otherwise misaligns some of the wooden parts, then the bees will build extra comb in the larger spaces, and fill the smaller ones with resinous propolis. Construction and renovation will continue until the appropriate bee space is again achieved.
Lorenzo Langstroth is credited as the Father of Modern Beekeeping because built the first functional hive that utilized the concept of bee space. He didn't discover the importance of this measurement, but he was the first to really utilize it in a functional way in a modern bee hive design. Earlier European innovators, including the Ukrainian Petro Prokopovych and the Polish Johan Dzierzon have been credited with its discovery. Swiss beekeeper François Huber also used the concept to create his "folio hive" that allowed observations inside the bees' nest. But Langstroth is credited with bringing the discovery of the bee space together with a practical and modular design that still bears his name 170 years later, and remains the most popular style of hive in the world. Many other types of bee hives have been developed and are in use in many places. But all of the most successful designs work because they are based on using the concept of the bee space -- the design that the honey bees themselves have been using for millions of generations!