Controlling dropwise condensation is fundamental to water-harvesting systems, desalination,
thermal power generation, air conditioning, distillation towers, and numerous other
applications. For any of these, it is essential to design surfaces that enable droplets
to grow rapidly and to be shed as quickly as possible. However, approaches based on
microscale, nanoscale or molecular-scale textures suffer from intrinsic trade-offs
that make it difficult to optimize both growth and transport at once. Here we present
a conceptually different design approach--based on principles derived from Namib desert
beetles, cacti, and pitcher plants--that synergistically combines these aspects of
condensation and substantially outperforms other synthetic surfaces. Inspired by an
unconventional interpretation of the role of the beetle's bumpy surface geometry in
promoting condensation, and using theoretical modelling, we show how to maximize vapour
diffusion fluxat the apex of convex millimetric bumps by optimizing the radius of
curvature and cross-sectional shape. Integrating this apex geometry with a widening
slope, analogous to cactus spines, directly couples facilitated droplet growth with
fast directional transport, by creating a free-energy profile that drives the droplet
down the slope before its growth rate can decrease. This coupling is further enhanced
by a slippery, pitcher-plant-inspired nanocoating that facilitates feedback between
coalescence-driven growth and capillary-driven motion on the way down. Bumps that
are rationally designed to integrate these mechanisms are able to grow and transport
large droplets even against gravity and overcome the effect of an unfavourable temperature
gradient. We further observe an unprecedented sixfold-higher exponent of growth rate,
faster onset, higher steady-state turnover rate, and a greater volume of water collected
compared to other surfaces. We envision that this fundamental understanding and rational
design strategy can be applied to a wide range of water-harvesting and phase-change
heat-transfer applications.