Why mosquito eggs float

This hand-coloured scanning electron micrograph is the winner of The EMBO Journal Cover Contest 2012. The image shows the surface of a mosquito egg (from Culex pipiens), which generates a water repellent network by connecting microscopically small structures to trap a thin layer of air.  The vitally important structures avoid immersion and enable the egg to float and aggregate with neighbouring eggs.

Female mosquitoes  lay clumps of eggs in standing water. Egg-rafts float for 2-3 days, until the larvae hatch. The water repellent nature of the egg is generated by microscopically small structures, which trap a thin layer of air.

source Martin Oeggerli sur micronaut.ch.
More info: http://www.mosquitoes.org/LifeCycle.html