Role of wing surface morphology of the Indian carpenter bee in self-cleaning and dew formation

We studied the surface morphology (micro- plus nanostructure) of Indian carpenter bee wings. In comparison with the Stenocara beetle's surface morphology or the lotus leaf surface morphology, the Indian carpenter bee wing shows a different type of surface morphology. It is observed that the two-tire surface morphology of the wings plays a key role in controlling wettability. The equilibrium contact angle (θ) and contact angle hysteresis (Δθ) measurement revealed that the carpenter bees' wings behave as superhydrophobic and self-cleaning for large water drops. Small drops formed by condensation nucleate in microchannels and ridges, grow through condensation and coalescence, and eventually become larger Wenzel or Wenzel-Cassie-Baxter type drops that lose their superhydrophobicity and self-cleaning property. Growth dynamics of condensed water drops on the wing surface show two distinguishing growth laws < R >  ~ t^α, α = 0.41 ± 0.03 in the initial state and < R >  ~ t^α, α = 0.99 ± 0.03 in the self-similar (coalescence-dominated) state with maximum surface coverage ≃ 0.45.