Finding honey bee eggs in brood combs is a necessary beekeeping skill. Understanding how they can indicate a queen problem is important to know in bee management. Knowing other aspects of bee-egg biology is fascinating and enriches our beekeeping experience.
In this article we will look at some historical observations along with the results of recent scientific studies. Hopefully the mix will be interesting since some of these information sources may not easily be accessed by beekeepers. But before we delve into the biology, let’s begin with a basic review on observing eggs.
A honey bee egg is about one-and-a-half millimeters long, cylindrically shaped, somewhat like a sausage, pearly white, and slightly bowed in the middle. A good method for seeing the eggs in comb is with bright sunlight coming over your shoulders. Hold the frame, containing young brood, in front of you. Position the frame at an angle so the light illuminates the floors of the cells without casting a shadow in them. In normal situations, the pattern should be one egg per cell, without too many missed or empty cells. The eggs should be near the centers of the cell floors (see Figure 1).
On cloudy days, the diffuse light is not good for observing eggs, but with practice it can still be done. Near sunset, at the end of a long workday inspecting colonies, the light becomes too dim to see eggs (although other apiary jobs can still be done for a while). To finish the day’s work checking for queen acceptance (by looking for her eggs), I have even used the headlights of the truck to find eggs, but sunlight works much better.
When looking for eggs, one can encounter the following optical illusion. After an adult bee emerges from her brood cell, other bees clean it. Especially in a dark brood comb illuminated by strong light, a bright white spot appears at the bottoms of these polished cells. Seeing an egg in this spot of white glare may be difficult. (Adjusting the angle of the frame a little may help.) This glare problem will return as we search for eggs.
With the arrival of swarm season, beekeepers will be out in their apiaries searching through their queen cups for eggs as a tentative sign toward the colony producing a swarm. (The bees may merely remove the eggs if variable spring conditions worsen, and the colony halts its swarming, at least temporarily.) A queen cup, sometimes called a queen cell cup, is a precursor of a queen cell, consisting of the cell base and about a third of the cell walls. Figure 2 shows a queen cup.
To speed up inspecting queen cups for signs of swarming, beekeepers just push back their cells walls (Figure 3). Distinguishing white eggs from the reflective glare coming from the bottoms of the cell floors can still slow one’s overall progression on a long workday, like when I am out checking top-bar hive combs in several apiaries (Figure 4).
Figure 5 shows a new queen cell where the bees have been depositing royal jelly, even before the egg hatches. The layer of royal jelly is just starting to turn a ghostly white. A very young larva in her royal jelly appears as a white shiny spot, appearing kind of wet. This “wet spot” of royal jelly is much easier to see than an egg. It indirectly tells the presence of a larva in most cells. Consequently, searching for newly hatched larvae is easier than eggs.
Finding a few empty queen cups does not indicate that the remaining cups are empty (allowing the beekeeper to examine only some queen cups and to prematurely conclude the colony is not preparing to swarm). The proper procedure for telling if a colony is preparing to swarm is to inspect all of the queen cups. Since queen cups occur throughout the brood nest, the entire brood nest should be inspected (like an inspection for older swarm cells since most of them come from queen cups). Even after smashing open all the queen cups, throughout the brood nest, expect the bees to rapidly rebuild them. The bees might not rebuild the same number of queen cups or put them at the same locations on the comb.
Returning to the problem of the glare in the cells, a long time ago it was encountered as an unknown optical illusion. The glare badly misled one investigator who was trying to understand how eggs were fertilized. In the 1700s, before it was well known that queens flew from the hive to mate, various ideas were proposed concerning the fertilization of eggs.
Mr. de Braw, an English naturalist, claimed to see a whitish liquid around eggs, different from the jelly surrounding newly hatched larvae. Furthermore, he claimed to see drones depositing fluid in these cells. He thought the drones sprinkled the eggs with sperm, and that was the (supposed) whitish liquid around eggs.1
While this assertion may sound absurd today, it is important to realize that many of even the basic facts of bee biology were not easy to understand correctly when investigators first grappled with them. Wrong interpretations, false starts, poor reasoning, or misleading prior information, just to name a few problems, could conspire to send a person’s thoughts down a path of permanent error (a possibility that still exists today). Nevertheless for de Braw’s assertion, a critical refutation came from an unlikely source.
From a careful series of experiments, François Huber, who was blind, and his servant Burnens, an intelligent, careful observer, discovered the truth. They found the cells containing the supposed fluid, and at first were convinced of its existence. Then came the critical observation:
… but we recognized the illusion afterwards, caused by the reflection of the rays of light; for we could see traces of the fluid only when the sun was sending its rays to the bottom of the cells. That bottom is usually lined with … cocoons of the worms which have successively hatched in it. Those cocoons are sufficiently bright and when strongly lighted there results an illumination, which is quite deceiving.
Huber investigated even further and had the cells dissected. No trace of the fluid could be found.1 Huber hypothesized that the reproductive fluid was nothing more than reflected light, and he was correct.
Another false theory concerned how the gender of the bee was determined. The queen lays most of the eggs in a colony. Her large abdomen is packed with a pair of ovaries, each consisting of about 180 threadlike ovarial tubules. A prospective egg, called an oocyte, moves though a tubule, becoming larger at the expense of about 48 other cells, called the nurse cells, that supply food to the developing egg.2 Just before the queen deposits an egg in a cell, she can fertilize it with sperm stored in a special organ called a spermatheca.
Under normal conditions, eggs laid in worker cells are fertilized and those laid in the slightly larger drone cells are not fertilized. Ever since Johannes Dzierzon discovered this selective fertilization in the 1840s, people have wondered how the queen performs this discriminating feat. One hypothesis was known as the “pressure theory,” whereby the smaller worker cell pressed on the queen’s abdomen causing the release of sperm, and thus egg fertilization. However, the “pressure theory” was refuted with several lines of evidence. First, the queen’s anatomy is not configured such that pressure from a cell would cause sperm release. Also, queens occasionally lay fertilized eggs in worker cells whose walls are not completely built and would apply little or no pressure on the queen’s abdomen. Moreover, queens lay fertilized eggs in queen cups, which are much wider than worker cells and should not press on her abdomen.
Later experiments revealed a much better explanation. Just before oviposition (the egg-laying position), the queen briefly inserts her head into the cell. At this time, her forelegs grasp the edges of the cell. This behavior is called “cell inspection” and is easily seen in ….