  Approximately half of the existing winged-insect species are of very small
size (wing length about 0.3-4 mm); they are referred to as miniature insects.
Yet until recently, much of what we know about the mechanics of insect flight
was derived from studies on relatively large insects, such as hoverflies, honey
bees and hawkmoths. Because of their very small size, many miniature insects
fly at a Reynolds number (Re) on the order of 10 or less. At such a low Re, the
viscous effect of the air is very large: A miniature insect moves through the
air as would a bumble bee move through mineral oil. Miniature insects must use
new flapping mode and new aerodynamic mechanisms to fly. Over the past decade,
much work has been done in the study of the mechanics of flight in miniature
insects: novel flapping modes have been discovered and new mechanisms of
aerodynamic force generation have been revealed; progress has also been made on
the fluid-mechanics related flight problems, such as flight power requirements
and flight dynamic stability. This article reviews these developments and
discusses potential future directions.
