The location where a bee lays its egg depends entirely on its species and social structure, reflecting the vast difference between the approximately 20,000 bee species worldwide. Most bees lead solitary lives; only a small fraction are social, living in large colonies with a queen and workers. In all cases, the female bee is solely responsible for selecting the site and provisioning the egg, ensuring the survival and development of the next generation.
The Wax Comb Cell in Social Hives
In social species like the honey bee, the egg is deposited into a precisely constructed wax cell within the hive’s honeycomb. Worker bees meticulously craft these hexagonal cells from secreted beeswax. The queen inserts her abdomen into the cell and places a single, tiny, white, rice-shaped egg directly onto the floor.
The size of the cell dictates the sex of the offspring. Standard-sized cells (around 5.2 millimeters) are used for female worker bees, while slightly larger cells are reserved for male drones. After the egg hatches, worker bees cap the cell with a porous wax cover, creating a protective nursery until the adult bee emerges.
Bumblebees are also social but use a less rigid structure than the honeybee comb. The queen initially constructs small, simple wax pots or a “brood clump” within the nest cavity, often in abandoned rodent burrows or bird boxes. She lays a batch of eggs (4 to 16) directly onto a mound of pollen and nectar. The queen then seals the clump with wax and sits on the structure, using muscle shivering for incubation to keep the brood warm.
Nesting Tunnels and Soil Burrows
The vast majority of bee species are solitary, creating a self-contained, sealed nursery for each egg. Approximately 70% of solitary bees are ground-nesters, such as mining bees. These females excavate tunnels into bare soil, sand, or clay, often preferring warm, south-facing slopes.
Within the main burrow, the female digs lateral tunnels, constructing a single brood cell at the end of each. She provisions this cell with a mixture of pollen and nectar (a pollen ball), lays a single egg on top, and then seals the cell with soil. This creates a secure chamber where the larva develops independently.
The remaining solitary bees are cavity-nesters, including mason bees and leafcutter bees, utilizing pre-existing narrow tunnels. These tunnels are often found in hollow plant stems, dead wood bored out by insects, or artificial bee houses. The female creates a linear series of cells within the cavity, using collected materials to build the separating walls.
Mason bees use mud or clay to construct the partitions between cells. Leafcutter bees cut precise, circular pieces from leaves and petals to construct and line their individual cells. In both cases, each cell is provisioned with a pollen-nectar mixture, an egg is laid, and the cell is sealed before the female creates the next one in the series.
The Process of Egg Selection and Placement
The female bee controls the sex of her offspring using haplodiploidy. Females develop from fertilized eggs (diploid, two sets of chromosomes), while males (drones) develop from unfertilized eggs (haploid, one set of chromosomes).
When laying an egg, the female controls whether sperm, stored in the spermatheca, is released to fertilize the egg as it passes through the oviduct. Releasing sperm results in a female egg; withholding it results in an unfertilized male egg.
This control allows the bee to match the sex of the egg to the available resources and space. In solitary nests, females often lay female eggs in deeper, protected cells and male eggs closer to the entrance. This ensures males, which typically emerge first, can leave without disturbing the developing females. For social bees, female worker eggs are placed in standard cells, and male drone eggs are placed in larger cells.