Leading Edge Vortices (LEVs) are generated whenever a viscous flow encounters an extreme change of direction or adverse pressure gradient.  They occur in many high Reynolds number flows including aerodynamic maneuvers, flapping flight and energy harvesting applications.  In this talk I will explore some aspects of LEVs generated by interactions between the flow and elastic structures.   We will use a model aeroelastic system  – a pitching wing supported by a torsional spring – to explore these phenomena.  This system exhibits a rich range of nonlinear instabilities,  dominated by the formation, growth and separation of LEVs. In a quiescent fluid, as might be found associated with hovering hummingbird flight, the LEVs result in a nonlinear fluid damping.  If the wing is immersed in a freestream flow, negative damping can be exploited to harvest energy from the oncoming flow as an appealing alternative to conventional rotary turbines.