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Modes of Insect Flight

Insect flight is complicated as compared to other biological fliers due to their small

mass, presence of elastic resilin at the wing joints and varieties of flexible flap-

ping wings adapted for high-frequency flight. These types of flight can broadly be

classified as follows:

(i)

Hovering Flight

(ii)

Forward Flight

(iii)

Gliding Flight

(iv)

Manoeuvring Flight

(v)

Passive Flight.

(i)

Hovering Flight: In hovering flight, forward velocity is nearly zero and

the flier remains in equilibrium more or less in a stationary condition. The

insect wing generates the necessary lift mainly during the downstroke and to

some extent during the upstroke. The hovering position is usefully adapted

for feeding such as nectar sucking from flowers and in some cases blood

sucking from its prey. The hovering also helps in the surveillance. The wing

span remains more or less constant and the wingbeat is continuous. During

hovering, the body axis is slightly inclined with the face upward and the wing

tip movements describe a figure of ‘8’. Hovering is a costly mode of flight in

terms of energy consumption. During hovering, the intake of oxygen as well as

the energy consumption increases by more than five times as compared to the

resting metabolic state. It may be noted that the hovering process results in the

creation of a set of standing vortices one above the other. This is in contrast to

the forward flight. Honey bees and Bumblebees are good examples of hovering

insects during nectar sucking. Hence, the insects must draw cleaner and fresher

air from the ambient flow and get rid of the vortices they have created to obtain

a periodic lift [2]. Basic aerodynamic mechanisms in hovering insects might

help in the development of insect-inspired Bio-mimicking MAVs [3–5]. The

swimming motion during hovering produces a figure of ‘8’ by the wing tips

which is an efficient one.

(ii)

Forward Flight: Insect flight is mainly due to a powerful downstroke and

an upward recovery stroke achieved through powerful muscular movements.

Forward flight of insects comprises of upward lift and forward thrust against

gravitational force and drag. Insects have less body mass and relatively larger

wing area per unit mass as compared to Homeotherm fliers (i.e. birds and bats)

and perform high wingbeat frequency flight. The low wingbeat frequency in

some insects comes under the category of Neurogenic fliers and it usually

ranges from 2 to 100 cps. The high wingbeat frequency in insects is known

as Myogenic and ranges from 100 to 1000 cps. The neurogenic fliers are also

known as synchronous fliers and the myogenic fliers as asynchronous fliers.

The forward velocity is usually variable from 1 to 4 m per second and is

influenced due to the small mass by the wind velocity. It is notable that when

insects fly forward, their stroke plane also becomes more inclined forward