Honey Bees’ Life Cycle: From Egg to Eclosion

The Honey Bee Life Cycle in Four Stages

Bees are holometabolous insects (undergo a change of form via complete metamorphosis) with four distinct developmental stages: egg, larva, pupa and adult bee. There are caste-specific variations in honey bees, based on diet, wax cell size or the duration from egg to adult, as summarised in the table below.

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Egg Stage

Honey bee eggs are white to clear in colour and are difficult to see with the naked eye. Sausage-shaped in appearance, the female eggs are fertilized, whereas the male are unfertilized. Both egg types look the same, and you can get an idea of what the egg will develop into by observing the wax comb: relatively larger cells for drones, smaller hexagonal cells for female worker bees and a larger, oblong cup/cell for the queen.

To lay eggs, the queen first “feels” for the cell with her forelegs to determine the cell size and then deposits an egg from her abdomen. The eggs are released with a glue¹ that sticks them upright in the cell, slowly falling to the bottom until they hatch.

Fertilized eggs can be raised as workers in hexagonal comb. Elongated cup-like cells on the bottom of frame means the colony is raising queens for swarming. The same elongated cells scattered throughout the frame are for supersedure or emergency queen rearing. Unfertilized eggs develop into male drones. The proof is simple – if a queen does not embark on a mating flight she will only lay unfertilized, “male” eggs.

Embryogenesis

The technical reader is referred to the citations.

Inside an egg, the undifferentiated clump of cells will grow into a structured larval shape through the actions of genes like wnt, hox, notch & dpp families (Pires-daSilva & Sommer, 2003; Fan et al., 2020; Chen et al., 2023). The embryonic development in bees is similar to many insects (such as the fruit fly model Drosophila melanogaster), with some variations. For example, a vital fruit fly spatial orientation gene, Bicoid, is missing in bees (Weinstock et al., 2006), whereas genes like Giant, Kruppel & Caudal (largely associated with the head, thorax & abdomen respectively) play a larger role in bees than fruit flies (Wilson et al., 2010).

This process occurs over three days until the egg hatches, with gene cascades (think one gene activating another gene with activates another gene…) guiding larval development, eventually generating that elongated, larval form.

At the completion of the egg stage, the shell dissolves leaving behind the larva on the bottom of the cell. This is unlike other insects (and reptiles), where the young emerge by cracking the shell open.

Larval stage

The larval stage lasts around 7 days for worker bees and is summarised as moulting and rapid growth. Within this stage, a brood pheromone is produced (E-β-Ocimene – Maisonnasse et al., 2010), which “signals hunger” to the nurse bees. Moulting is important as the insect exoskeleton is rigid and does not expand as our bones do. The larva sheds its exoskeleton (moulting) and reforms a larger one², which also provides it with an opportunity to change its structure.

Regardless of caste, honey bees have five instars (& six moults, depending on the literature cited). It is in the last two moults that caste-based differentiation is visible. The larva grows rapidly, and then the cell is stocked with food and capped by the nurse bees. Immediately after capping, the larva moves into an upright position and begins to line its cell with a thin cocoon from silk produced by its salivary glands (Sutherland et al., 2006).

The fifth instar stage takes around 36 hours, and features the final shedding of the larval cuticle as the grub forms its first pupal structure (also termed the “prepupal stage” in literature). In this stage, the gut development is completed, which enables defecation.

The continuous defecation & shedding of cuticles of the larvae inside cells is one reason why bees and beekeepers replace old comb, since it leads to a reduction in cell volume, which results in smaller adult bees, and also a buildup of nutrients that are favoured by hive pests like wax moth larvae.

Pupal stage

For a worker bee, the pupal stage occurs over the next twelve days as the adult form emerges. This process occurs in regions containing previously undifferentiated cells (imaginal discs). In other words, there are clumps of cells on the pupa that get activated and begin forming structures like the legs and wings. The science behind this process is poorly understood, as there is a massive rearrangement of internal anatomy (Leichtenstien et al., 2018; Tian et al., 2018):

• In the abdomen: degrading and reforming the larval intestine and heart tubes, and rebuilding them from the remaining undifferentiated stem cells.

• In the head: development of the optic (vision) and antenna lobes in the brain, as well as the fusion of ganglia (nerve bundles) in the ventral nerve cord.

• All over: pigmentation of the body, from the larva stage’s milky white into the black of adult bees (it is the hairs that make them yellow, not their skin tone)

  • The eyes are the first to gain colour and beekeepers can see this by uncapping older brood cells.

The hardening and colouration of the cuticle is the pharate (“hidden”) stage (Elias-Neto et al., 2009). The bee now sheds its pupal cuticle, and begins emerging from the cell. As these processes occur simultaneously, parts of the cuticle remain attached to the emerging bee. This early eclosion (as opposed to exiting after the cuticle hardens) means that the new bee’s exoskeleton is still soft. For the first few days of life, the adult worker bee is relegated to cleaning duties as it cannot fly or sting, and you can identify her by the hairier body and lighter colourations relative to nestmates.

Adult Bee

At this stage the honey bee life cycle is largely complete. The adult bee’s role in the hive are differentiated based on caste.

Worker Bees

Under normal circumstances, the adult worker bee’s role in colony is based on her age:

• Around ages 1-3 days, the worker bee cleans cells to prepare them for brood rearing or resource storage.

  • She cannot fly or sting yet, as her cuticle is still soft.

• At 3-10 days, she is a nurse bee who feeds larva and produces royal jelly.

  • Some may become part of the queen bee’s retinue at ages 7-12, feeding and caring for Her Majesty.

• Around 12 days old, their wax glands mature and they become wax producers, building and repairing the comb.

  • Bees not involved in comb building process incoming nectar and pollen from returning foragers, both for storage and bee bread production.

• The more mature and physically-capable middle aged bees become hive entrance guards.

• At 22 days and above, the worker bee spends her remaining life as a forager, obtaining nectar, pollen, water, and propolis. This can last for a few weeks during the spring and summer, with an average lifespan of 42 days; 20 days of foraging.

Queen Bee

For Her Majesty the Queen:

• The first few days of life, she may compete with other queens for dominance (if reared with other queen cells for swarming).

• If there are no rival queens, then she remains inside the hive, feeding and growing until she attains sexual maturity.

• Around 1-2 weeks old, the queen conducts her mating flight, and returns to the hive to lay eggs. For the remainder of her life (several years), she will continue to lay eggs.

  • I remind the beekeeper to replace every two years to maintain optimal brood production. See Requeening a hive for more.

Drone Bee

Like many males, drones do not do much inside their home. Their first few days are spent being fed and cared for by the worker bees (they cannot feed themselves) until they reach sexual maturity (1-2 weeks). At this stage, the drones perform their orientation flights and proceed to the drone congregation areas (distinct areas in the sky containing large numbers of drones), awaiting the virgin queens.

The drone will do this daily until death (up to 55 days old). Should the drone mate with a queen, then death comes sooner, as they die following ejaculation.

Nutrition and Honey Bee Development

For Queen development – see Factors Affecting Queen Bee Health

Worker bees produce food from two glandular secretion – the hypopharngyeal gland and the mandibular glands (Reviewed in Bortolotti & Costa, 2014). All eggs are fed with a combination of these secretions. Those destined to become queens receive a 1:1 ratio of the glandular secretions (the royal jelly), whereas eggs that become workers receive a secretion favouring mandibular gland contents.

The difference between the foods is in sugar content, with royal jelly containing a higher concentration. Kaftanoglu and colleagues (2011) showed that if a worker larva was fed worker jelly with extra sugar, she would develop into a queen bee. Of course, it is likely that other factors are involved, and sugar concentration is a more noticeable one.

Beekeepers observing queen cups will note that they are always floating in royal jelly, whereas worker cells contain “just enough” food for the developing larvae – an adaption for dedicating resources? From the third instar onwards, worker larvae are fed bee bread, mixture of worker jelly and pollen.

Hormones Driving the Honey Bee Life Cycle

The technical reader is referred to the citations.

Several hormones are involved in honey bee development, with Insulin and Insulin-like signalling, as well as the TOR pathway (target of rapamycin – mTOR in mammals) controlling the rate of growth and nutrient signalling, whereas the juvenile hormone and ecdysteroids control moulting, as in other insects (Reviewed in Li et al., 2019).

As the name suggests, juvenile hormone is found in the younger insect, with its concentrations lower in the adult bee. Its concentrations are higher during the molting stages, such as the third and fifth instars in queen bees (Withers et al., 1995 & Fahrbach & Robinson 1996). Juvenile hormones controls ecydsteriod synthesis and release, and also affects ovary development in the female bees (Wynants et al., 2023).

TOR is more involved in queen development than workers, with RNAi knockouts resulting in queens with worker-like features, even if the larvae is fed a queen’s diet (Patel et al., 2007). TOR sets the larva’s growth rate so that it reaches an optimal size for the juvenile hormone to commence moulting downstream. These pathways are fundamental to insect growth, and disrupting them can have multiplicative effects which cannot be explained by a single observation – it is a domino effect.

There are also epigenetic changes involved in honey bee development (Shao et al., 2014) – these are inherited traits that are not a result of DNA modification (which is the basis of evolution by natural selection). Methylation of cystine bases and histone modifications are such examples, and the interested reader can refer to the literature for more information.

How Many Honey Bees can Live in a Beehive?

Tens of thousands bees can live in a single hive; well over 50,000 in the peak season. The population is influenced by factors like the queen’s egg laying capacity and forage availability. It takes a lot of nutrients to raise an adult bee, and even more so in the case of a queen. When all needs of the colony are met, then brood rearing is optimized. More brood, more foragers. More foragers, more honey for the beekeeper.

Various signals and pheromones act on the worker bee during her adult life stage to determine her role inside the hive, and when to shift between taskings.

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Footnotes

1. This is common in female insects. Egg glue proteins are produced to anchor their eggs in a specific orientation within the cell (upright in this case), and are made by the Dufour glands in queens (Katzav-Gozansky et al., 2001). ↩︎
2. Some definitions: the period between moults is termed “instar”. “First instar larva” begins at hatching, second instar is after the first moult, third instar for the second moult and so on. The “exoskeleton” is the entire outer body of an insect, whereas the cuticle is the outermost layer (itself containing four layers). Moulting occurs in the cuticle. ↩︎