Odonates are mostly sit-and-wait predators. They perch on solid surfaces and will take off after small insects as they fly by. Once in flight, dragonflies swoop upwards from below their flying prey, and grab the prey with their outstretched legs (Olberg, Venator & Worthington, 2000). In flight, gliding allows them to save energy as compared to flapping. Gliding was also thought to help in thermoregulation in dragonflies (Zhang and Lu, 2009).
In the flight of Anisoptera, their body lies almost horizontal. They use an asymmetric rowing motion: wings push backward and downward, and at the end of the stroke, feather and slice upward and forward. This rowing motion occurs along an inclined stroke plane. This way of flight is different from other flying insects, where by they use a symmetrical back-and-forth stroke along a horizontal stroke plane. One advantage of this method of flying is that upward drag created during the down-stroke is able to support majority of the body weight of the dragonfly (Wang, 2008).
Odonates are also known to have high predation efficiency due to their powerful sight. We will explain in detail the structures involved below:
Image from:
http://www.asia-dragonfly.net/globalResults.php?Species=1301&offset=10
In the flight of Anisoptera, their body lies almost horizontal. They use an asymmetric rowing motion: wings push backward and downward, and at the end of the stroke, feather and slice upward and forward. This rowing motion occurs along an inclined stroke plane. This way of flight is different from other flying insects, where by they use a symmetrical back-and-forth stroke along a horizontal stroke plane. One advantage of this method of flying is that upward drag created during the down-stroke is able to support majority of the body weight of the dragonfly (Wang, 2008).
Odonates are also known to have high predation efficiency due to their powerful sight. We will explain in detail the structures involved below:
· Wings
The odonates’ wings are highly grooved. This grooving helps to increase the stiffness and strength of the wing, resulting in a lightweight structure, thus allowing good aerodynamic performance (Jongerius and Lentink, 2010). Cytological evidence has shown that the flight muscle fibers of both the Zygoptera and Anisoptera are very much similar, except that in Zygoptera, they have pairs of lamellar fibrils alternating with the mitochondria instead of single fibrils in that of Anisoptera (Smith, 1966).
· Flight
Separate muscles control the fore and hind wings of the Anisoptera, and this allowed the rise of the distinctive feature of a dragonfly’s wing movement: their unique phase relation between the fore and hind wings. During takeoff, the wings of the dragonfly are observed to beat in phase. However, this is not the case when flying. During hovering, their fore and hind wings beat out of phase. Why so? Wang (2008) hypothesized that the alternating down stroke in flight may have helped to reduce body oscillation. Experimental results from Wang (2008) showed that the hypothesis was only one of the reasons for such variation in maneuver. Since the fore and hind wings of an Anisoptera are approximately a wing-width apart, this distance is close enough for hydrodynamic interaction between them. By beating out of phase, the fore and hind wings approaches each other from opposite sides and cross near the mid stroke. This allows the fore wings to experience a stimulated flow due to the hind wings, and vice versa. As a result, the drag on the wings is reduced significantly. With reduction in the drag, energy exerted by the Anisoptera is greatly reduced. Therefore this counterstroke motion allows the Anisoptera to generate equivalent amounts of force for flight as other insects, while saving aerodynamic power (Wang, 2008).
· Visual
The odonates’ wings are highly grooved. This grooving helps to increase the stiffness and strength of the wing, resulting in a lightweight structure, thus allowing good aerodynamic performance (Jongerius and Lentink, 2010). Cytological evidence has shown that the flight muscle fibers of both the Zygoptera and Anisoptera are very much similar, except that in Zygoptera, they have pairs of lamellar fibrils alternating with the mitochondria instead of single fibrils in that of Anisoptera (Smith, 1966).
· Flight
Separate muscles control the fore and hind wings of the Anisoptera, and this allowed the rise of the distinctive feature of a dragonfly’s wing movement: their unique phase relation between the fore and hind wings. During takeoff, the wings of the dragonfly are observed to beat in phase. However, this is not the case when flying. During hovering, their fore and hind wings beat out of phase. Why so? Wang (2008) hypothesized that the alternating down stroke in flight may have helped to reduce body oscillation. Experimental results from Wang (2008) showed that the hypothesis was only one of the reasons for such variation in maneuver. Since the fore and hind wings of an Anisoptera are approximately a wing-width apart, this distance is close enough for hydrodynamic interaction between them. By beating out of phase, the fore and hind wings approaches each other from opposite sides and cross near the mid stroke. This allows the fore wings to experience a stimulated flow due to the hind wings, and vice versa. As a result, the drag on the wings is reduced significantly. With reduction in the drag, energy exerted by the Anisoptera is greatly reduced. Therefore this counterstroke motion allows the Anisoptera to generate equivalent amounts of force for flight as other insects, while saving aerodynamic power (Wang, 2008).
· Visual
In odonates, there are eight bilateral pairs of target-selective descending neurons (TSDNs) responsible for transmitting visual information about moving objects such as a flying prey from the brain to the thoracic ganglia (Olberg 1981, 1986; Frye and Olberg, 1995). Two of the eight TSDN pairs have receptive fields along the visual midline, are responsible for detecting small objects. The remaining six pairs have larger receptive fields, which are responsive to a wide range of object sizes. Only one pair of TSDN is directionally selective. It is the electrical stimulation of individual TSDNs that produce the steering movements of the wings (Olberg 1983). The receptive fields of TSDN are located in the forward and upward quadrant of visual space, which is in the direction of the prey immediately before capture. Therefore, the function of TSDNs is said to be involved in the steering of flight towards moving objects (Olberg, Venator & Worthington, 2000).
· Predation
Experiments conducted by Olberg, Venator & Worthington (2000) from observing odonates’ prey-pursuit flight path uncovered a strategy employed by them for predation, that is: they intercept their prey in its flight path. This method of predation is different from other insects like flies (Land and Collett 1974) and beetles (Gilbert 1997). Generally, these insects direct their pursuit towards the currently perceived position of their prey. Odonates, on the other hand, direct their flight paths to a point in front of the prey, hence is said to be able to predict their prey’s flight path (Olberg, Venator & Worthington, 2000).
In order for a successful flight interception, odonates have to steer themselves in a way, so that they maintain the sight (image) of prey at a constant retinal position. For an odonate to plan their flight path, they must be able to estimate the prey distance. To do this, they make use of the time-course of the prey’s angular speed. The velocity profile might not indicate the specific size and distance of the passing prey, but it serves as an alert to the odonate that a flying insect is nearby (Olberg, Venator & Worthington, 2000).
Dragonflies can maneuver themselves in such a way to minimize the lost of sight of their prey in all directions with their amazing flight efficiency. This is a closed-loop strategy, meaning that the odonate does not head for a known point of interception, but rather knows how to get to that point simultaneously with the arrival of the flying prey. Hence it results in successful predation (Olberg, Venator & Worthington, 2000).
· Predation
Experiments conducted by Olberg, Venator & Worthington (2000) from observing odonates’ prey-pursuit flight path uncovered a strategy employed by them for predation, that is: they intercept their prey in its flight path. This method of predation is different from other insects like flies (Land and Collett 1974) and beetles (Gilbert 1997). Generally, these insects direct their pursuit towards the currently perceived position of their prey. Odonates, on the other hand, direct their flight paths to a point in front of the prey, hence is said to be able to predict their prey’s flight path (Olberg, Venator & Worthington, 2000).
In order for a successful flight interception, odonates have to steer themselves in a way, so that they maintain the sight (image) of prey at a constant retinal position. For an odonate to plan their flight path, they must be able to estimate the prey distance. To do this, they make use of the time-course of the prey’s angular speed. The velocity profile might not indicate the specific size and distance of the passing prey, but it serves as an alert to the odonate that a flying insect is nearby (Olberg, Venator & Worthington, 2000).
Dragonflies can maneuver themselves in such a way to minimize the lost of sight of their prey in all directions with their amazing flight efficiency. This is a closed-loop strategy, meaning that the odonate does not head for a known point of interception, but rather knows how to get to that point simultaneously with the arrival of the flying prey. Hence it results in successful predation (Olberg, Venator & Worthington, 2000).