Insect Flight
A. Wing Structure
B.  Flight Mechanism
C.  Evolution of Flight
Wings tend to have
less venation and
be more stiff in
insects with
faster wing speed
epidermis
epidermis
cuticle
cuticle
cuticle
Not all hexapods have wings
-- 5 primitive orders have never developed wings
(known as Apterygote insects)
ex. collembolans, springtails
-- highly specialized insects without wings
parasites such as fleas and lice
castes of social insects--worker ants, termites
--functional wings occur only in the imago
1
Wings don’t operate in the same way in all insects
Examples:
-- dragonflies and grasshoppers: 2 pair of wings;
Dragonfly wings beat at the same frequency but not
necessarily in synchrony. Front wings of grasshopper not
used for flight.
Wings don’t operate in the same way in all insects
-- beetles: front wings have become heavy shields (elytra)
and only hindwings serve for flight.
--Hemiptera forewings only partly cover hindwings
Coleoptera
Hemiptera
Wings don’t operate in the same way in all insects
-- butterflies and moths, bees and wasps: wings are
interlocked and their strokes are in synchrony
2
Wings don’t operate in the same way in all insects
Example:
-- diptera: front wings used in flight; 2nd pair modified as
halteres, which act as a gyroscope to provide balance
Robber fly
Figure 1 Halteres, the 'gyroscopic' sense organs of the blow fly Calliphora vicina. During walking and flight,
the halteres oscillate in a vertical plane around a proximal hinge, and Chan et al.3 have now shown that they
are under both neural and visual control. a, The halteres (arrowhead) are found between the thorax and
abdomen of a fly. b, Left haltere from above. Most of the mass of the haltere is in the knob (left). A thin, stiff
stalk leads to a base that houses about 335 cuticular strain receptors
Insect Flight
A. Wing Structure
B. Flight Mechanism
C. Evolution of Flight
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B. Flight Mechanism
Is Complex and Involves
•  Flight muscles that aren’t part of the wing
•  Elastic property of a substance called
resilin present in the hinges of wings
•  Elastic properties of the thorax itself
1. Thorax-Wing Structure
3 thoracic segments, 2nd and 3rd bearing wings
Each segment is comprised of:
wing
notum
a) a dorsal plate called a notum
pleurons
apodemes
b) ventral plate called a sternum
c) 2 side plates, each called pleurons
Apodemes serve as interior
attachment sites for muscles
sternum
Thorax-Wing Structure
The wings are attached to the
thoracic segments at 3 points:
anterior notal process (notum)
posterior notal process (not shown)
3 pleural wing processes (pleuron)
wing
notum
4
Thorax-Wing Structure
Schematic view
(dorsal plate)
(side
plate)
2. Flight muscles: there are 2 types
Direct : attached to the wing itself
Indirect: not attached to the wing but to the
notum (dorsal) and sternum (ventral)
Attached
Anteriorly and
posteriorly to
Phragma
Direct
muscles
indirect muscles
Contraction Times of Invertebrate Muscle
Source
Time (seconds)
Anthozoan muscles
5-180
Scyphozoa
Earthworm Circular Muscle
Bivalve Byssus Retractor Muscle
Gastropod Tentacle Retractor
Horseshoe Crab Abdominal Muscle
Insect Flight Muscle (striated)
0.5 - 1
0.3-0.5
1
2.5
0.195
0.025
~ 40 beats per second
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Insect
speed
Dragonfly
Beetles
Butterflies
Hawk moth
Mosquito
Midges
Honey bee
Beats
/second
20-28
46-90
9-12
70
300-550
1000
200
Flight
km/hour
25
5
9
18
32
22
22
Movement - body lengths per second
human - 5
Volkswagen 'beetle' - 5
jet fighter plane - 100
fly - 250 to 300
In all insects, the upstroke is affected by contraction of
indirect flight muscles; this results in the notum being
pulled down toward the sternum. A fulcrum point
at the pleural process forces the wing up
(indirect)
In butterflies and moths, beetles, grasshoppers,
roaches, dragon flies and others, the downstroke is
powered by the direct flight muscles in conjunction
With the relaxation of the indirect muscles
End of upstroke
Downstroke
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In insects such as bees, wasps, and flies the
downstroke is also achieved by indirect muscles called
the dorsal longitudinal muscles
3. Neural control of wing movement:
synchronous: single volley of nerve impulses
stimulates a single muscle contraction and
therefore one wing stroke
asynchronous: only occasional nerve impulses are
necessary to maintain wing movement. Storage of
potential energy in the resilient part of the thoracic
cuticle causes multiple wing strokes after a single
muscle contraction; interaction of antagonistic
indirect flight muscles is also important
Wing hinge contains
Resilin, an elastic
protein that returns
Nearly 95% of the
Kinetic energy that is
delivered to it.
Insects with asynchronous control generate much faster
wing speeds: flies 300 beats/sec midges 1000 beats/sec
Butterflies, which have synchronous control: 4 beats/sec
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Click mechanism
wing
In many insects, especially those with Asynchronous
control, a “click” mechanism causes wings to be stable
only in the complete up or down position
Flying is more than upward-downward wing strokes.
For effective flight the angle of the wing on the upward
and the downward stroke cannot be the same.
Direct muscles alter the angle of the wing to
maintain a net thrust.
View
of the leading
edge angle of
the wing
during the up
and down
strokes of
a flying insect
Lift and Thrust
Basic principles of fixed wing
aerodynamics fail to explain how
some insects achieve flight.
Flight of the Bumblebee
Bumblebee in Flight
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According to the most recent studies, the
insect wing stroke provides lift in three
previously unknown fundamentally different ways:
-- as a “classical” airfoil
-- by generating vortices behind the leading edge
-- rotational lift
-- wake capture
Rotational
Vortex
Leading
Edge Vortex
Rotational
Vortex
Image of hovering vortices. In general,
cool colors represent clockwise motion and
warm colors counterclockwise. The figure-8
motion of the wing (shown here in black,
with the leading edge toward the Y axis)
has produced clockwise (blue and green) as
well as counterclockwise (red) vortices.
till
Vortex Video
DOWNSTROKE. In this example, as a fly moves from right to left during a downstroke of its
wings (top),blue arrows indicate the direction of wing movement and red arrows the direction
and magnitude of the forces generated in the stroke plane.
During this phase, the insect has at its disposal two means of generating lift. Delayed stall (1)
causes the formation of a leading-edge vortex that reduces pressure over the wing. Rotational
lift (2) is created when the insect rotates the angle of its wings (dotted line), creating a
vortex similar to that of putting "backspin" on a tennis ball. At its completion (3), the
maneuver also results in a powerful force propelling the insect forward.
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UPSTROKE. As the insect drives its wing upward, it has the option of using another
mechanism to gain lift--wake capture. This gains an insect added lift by recapturing the
energy lost in the wake. As the wing moves through the air, it leaves whirlpools, or
vortices, of air behind it (4). If the insect rotates its wing (dotted line), the wing can
intersect its own wake and capture its energy in the form of lift (5).
Insect Flight
A. Wing Structure
B. Flight Mechanism
C. Evolution of Flight
Evolution of Wings: not well understood.
Earliest insects included both flying and non flying types
There are two theories:
1) paranotal theory: wings developed from paranotal
lobes that were first used for gliding. But how did
flight musculature originate?
Fossil insects with
paranotal lobes
10
Evolution of Wings: not well understood.
Earliest insects included both flying and non flying types
There are two theories:
1) paranotal theory: wings developed from paranotal
lobes that were first used for gliding. But how did
flight musculature originate?
2) branchial theory: wings developed from
gills that were subsequently used for swimming,
and finally for flight.
WHAT IS THE EVIDENCE?
•  Mayfly ancestors were probably the
first flying insects
•  Some species with reduced wings
(brachyptery) are unable to fly and use
wings as fins for swimming
•  Comparisons with fossils indicate that
brachyptery may have been common in
early insects
Madagascar
Mayfly
Skims the
surface of
streams
Evolution of Wings: not well understood.
Earliest insects included both flying and non flying types
There are two theories:
1) paranotal theory: wings developed from paranotal
lobes that were first used for gliding. But how did
flight musculature originate?
2) branchial theory: wings developed from
gills that were subsequently used for swimming,
and finally for flight.
WHAT IS THE EVIDENCE?
11
Discussion of Molecular Evidence:
expression of pdm/nubbin
and apterous genes
Evolution of Wings: not well understood.
Earliest insects included both flying and non flying types
There are two theories:
1) paranotal theory: wings developed from paranotal
lobes that were first used for gliding. But how did
flight musculature originate?
2) branchial theory: wings developed from
gills that were subsequently used for swimming,
and finally for flight.
WHAT IS THE EVIDENCE?
12