Correct answer: 3.
Because workers can enter deep into the cell and displace the egg during certain behaviours, notably linked to thermoregulation.
Why?
After laying, the egg remains fixed in the cell until the larva hatches. Video observations suggest that the apparent change of position is not simply due to gravity, nor to a modification intended to feed the egg. It can be explained by the activity of the workers, which penetrate deep into the cell and may push back or tilt the egg.
What to understand
In the brood nest, the workers do not merely feed the larvae. They inspect the cells, take part in the upkeep of the brood and contribute to the thermal regulation of the comb. Some bees can enter very deep into a cell, remain motionless for a moment and act as a source or relay of heat. This contact can alter the visible position of the egg.
What to remember
The position of the egg gives a useful indication of its age, but it should not be interpreted as an autonomous embryonic mechanism. In practice, an upright egg indicates very recent laying, whereas a recumbent egg often signals imminent hatching, with a margin linked to the observations and the conditions of the colony.