Water depth
When egg-laying was allowed in three containers of the same diameter but with the water levels 25 mm, 50 mm and 75 mm below the rim, nearly 60% of all eggs laid were found in the container with the highest water level. In this container, 78 % of the eggs were deposited within 5 mm of the water surface, while in the deepest container there was a greater spread of
eggs towards the upper rim (Surtees, 1960c).