Jumping in a winged stick insect
Department of Zoology, Downing Street, University of Cambridge,
Cambridge CB2 3EJ, UK
Present address: Department of Physiology, Royal Free and University College
Medical School, London NW3 2PF, UK
* e-mail: mb135{at}hermes.cam.ac.uk
Accepted 16 May 2002
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Summary |
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A forward jump of both adults and nymphs involves movements of the abdomen and the middle and hind pairs of legs. The abdomen is raised and swung forwards by flexion at the joint with the metathorax and at the joint between the meso- and metathorax. At the same time, the tibiae of the hind and middle legs are extended and their femora depressed. The femoro-tibial joints of the legs are not fully flexed before a jump, and no structures in these joints appear to store muscular energy. The whole jumping sequence takes approximately 100 ms and results in take-off angles of 10-35° at velocities of 0.6-0.8 m s-1 and with an acceleration of 10 m s-2. The abdominal angular velocity was 2000° s-1 and the tip of the abdomen moved at linear velocities of some 1 m s-1, while the maximum rate of tibial extension was 4000° s-1.
Rapid backward movements result either in the collapse of the body onto the ground, with a displacement away from the stimulus of approximately half a body length, or in the propulsion of the insect off its perch. Neither movement involves curling of the abdomen.
From a horizontal posture, the forward jumps result in a displacement of a few body lengths. More lift can be generated in adults by elevating the hind wings as the abdomen is swung forwards and depressing them as the legs lose contact with the ground. In this way, jumps can lead directly to flapping flight. Take-off into flight can, however, be achieved without the abdominal movements seen during jumping.
From a vertical posture, a forward jump propels the insect upwards and backwards before it falls to the ground horizontally displaced from its perch. Backward movements result in the insect falling with little horizontal displacement from its perch.
Key words: kinematics, joint mechanics, locomotion, Sipyloidea, Thailand winged stick insect, Sipyloidea sp
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Introduction |
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Stick insects usually have an elongated body shape that closely resembles
the branches of plants on which they climb, perch and feed. They respond to a
threat by freezing their body position catalepsy
(Bassler, 1983;
Bassler and Foth, 1982
;
Bassler et al., 1982
;
Driesang and Büschges,
1993
; Godden,
1974
) enabling them to remain motionless for long periods
and, therefore, to become difficult for predators to detect amongst
vegetation. Nevertheless, some stick insects have active defensive displays
and active escape responses. In some, the hind wings and the modified front
wings are raised to increase the apparent size of the insect and to reveal
previously hidden patches of colour
(Bedford, 1978
). These
movements may be accompanied by buzzing
(Rehn, 1957
) or swishing
(Bedford and Chinnick, 1966
)
sounds generated by rubbing the front and hind wings together or by rubbing
the two antennae together (Henry,
1922
). In other species, the hind legs are spread apart, often to
reveal patches of colour, and then struck together. If a male Onctophasma
martini is grabbed, it will curve its abdomen dorsally and forwards while
the femoro-tibial joints of the hind legs are flexed
(Robinson, 1968b
). Males of
Eurycantha calcarata and E. horrida raise their abdomen in a
similar way but then evert the copulatory organ to release an odour
(Bedford, 1976
). They will also
swing the hind legs together to trap and impale an offending object on their
femoral spines. Anisomorpha buprestroides squirts a deterrent spray
at its predators from glands in the thorax that open just behind the head
(Eisner, 1965
). These startle
responses may grade into active escape responses. Orxines macklotti
(Pseudodiacantha macklottii) curls its abdomen forwards and jumps
from its vertical perch before dropping to the ground
(Robinson, 1968a
), and the
males of Onctophasma martini push off from their perch while the
females simply drop (Robinson,
1968b
). Metriotes doicles and Bacteria ploiaria
also jump (Robinson, 1969
).
The net result is a backward movement because the common posture is vertical
with the head pointing upwards.
All the descriptions of these escape movements of stick insects have been brief and preliminary. We have, therefore, used high-speed imaging to analyse the detailed movements involved in escape responses of the Thailand winged stick insect Sipyloidea sp. This stick insect has an elongated body shape with long thin legs and an ability to show catalepsy, but has an unusual mechanism of jumping. We show that it jumps forwards from a horizontal stance by flicking its abdomen forwards and then backwards while extending the middle and hind pairs of legs. From a vertical posture, a jump using the same movements launches it into a backward and downward movement. In the winged adults, jumping may propel the animal into flapping flight.
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Materials and methods |
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To measure the distribution of mass within different parts of the body,
adult males and females were weighed, frozen and then reweighed to check that
there had been no change in mass during the freezing process. Body parts were
removed sequentially and the carcass reweighed at each stage. Body length and
the lengths of the different segments of the three pairs of legs were also
measured and compared with data for other stick insects and selected
orthopterans (Burrows and Morris,
2001). The resting posture was observed in large cages containing
branches of bramble. Behavioural responses to an initial tactile stimulus to
the abdomen and a second stimulus applied 5 s after the response to the first
had stopped were analysed in the same surroundings. Tactile stimuli were
applied to the head in a separate series of experiments.
Jumps were induced by a light touch with a fine paint brush or by gently tapping a 20 mmx70 mm Styrofoam platform raised on a pillar some 200 mm from the bench. The unrestrained insect stood on the horizontal or, when rotated by 90°, the vertical surface of this platform. Images were captured directly to a computer with a Redlake Motionscope (Red lake Imaging, San Diego, CA, USA) at a rate of 250 Hz and with an exposure time 1/1000 s. Selected images were analysed with the Motionscope camera software (Red lake Imaging) to obtain the coordinates of the various parts of the body and legs. These data were then imported into Excel (Microsoft), where angles were calculated. Seventy-seven forward jumps from a horizontal starting posture by 20 stick insects, 40 jumps from a vertical posture by 10 insects and 21 rapid backward movements by 14 insects from a horizontal posture in which the take-off trajectory was at right angles to the optical axis of the camera were captured and analysed. With this orientation, the legs project laterally from the body at angles that change as the coxae are rotated at the joints with the thorax. This leads to error in measurements of the absolute femoro-tibial angle, but the analyses of this joint are focused on its angular changes during a jump. We also estimate that the measurements of take-off velocity from the frame rate we used (250 Hz) could lead to an error of ±0.05 m s-1 and that this will carry forward into other calculations.
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Results |
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Only the adults have wings. The hind wings are long (50 mm in females, 35 mm in males), whereas the front wings are short (8 mm in females, 5 mm in males). Males could gain height in flapping flight, but the flights of the heavier females were infrequent and usually resulted in a loss of height.
The three pairs of legs are all long and thin. The front and hind pairs of legs are similar in length and the middle legs slightly shorter so that the ratio of femoral lengths is (front:middle:hind) is 1:0.7:1. In males, the total length of either a front or a hind leg was 68% of the body length, and in females it was 50%. The front legs frequently did not support the weight of the body and were instead often extended anteriorly off the ground (Fig. 1A). The femur of a hind leg was approximately 8% larger dorso-ventrally than the mesothoracic femur, but no differences were apparent in the structure of the femoro-tibial joint compared with the other legs. There are no prominent semi-lunar processes, but there are curved grooves on both the medial and lateral surfaces of the cuticle. The extensor and flexor tibiae muscles of both meso- and metathoracic legs insert on similar sites on the dorsal and ventral surface of the tibia respectively.
Resting posture
To determine the orientation of the body normally adopted by the stick
insects, observations were made of two cages each containing 30-40 insects.
The undisturbed positions adopted by large nymphs or adults fell into four
broad categories (Fig. 2A): (i)
vertical, head-up, perched on a twig or the side of the cage with the body's
long axis perpendicular to the floor and the head pointing upwards; (ii)
vertical, head-down, as for vertical, head-up, but with the head pointing
downwards; (iii) horizontal, upright, standing on the floor or a twig with the
body's long axis parallel to the floor; and (iv) horizontal, upside-down,
upside-down on the ceiling of the cage with the body's long axis parallel to
the floor.
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A chosen posture could be maintained for long periods, often with no apparent movement. Most male and female adults and nymphs tended to assume the first posture. Adult males were found upside-down on the ceiling more frequently than females or nymphs. We selected two specific starting postures to analyse jumping movements because it was from these that jumps were most frequently initiated: (i) horizontal and upright and (ii) vertical and head-up.
Avoidance and escape movements
Tactile stimulation caused the stick insects to respond in different ways
(Fig. 2B-D), with some
responses more common than others, and there was evidence of differences
between adult males, adult females and nymphs. The responses to stimulation of
the abdomen were categorised as follows: (i) freeze/no response, no overt
movement and resting posture maintained; (ii) withdraw, rapid retraction of
the legs and forward curling of abdomen, often holding it in this flexed
position; (iii) walk, walking for two or more steps away from the point of
stimulation; (iv) jump, rapid flicking of the abdomen accompanied by extension
of the middle and hind legs, resulting in a jump; and (v) fly, adults opened
their wings and took off with or without a preceding jump.
The most frequent response of adult females to both the first and second stimulus was rapid withdrawal and curling of the abdomen. Their next most common response to the first stimulus was to freeze and, to the second, to walk away (Fig. 2C). Males and nymphs froze, withdrew or walked away from the first stimulus but more frequently walked away from the second stimulus. Jumping was more common in response to the second stimulus for all three groups. Only adult males took off into flapping flight when stimulated. On the assumption that the order of activity was represented by the sequence freeze<withdraw<walk<jump<fly, responses of all insects to the second stimulus tended to be more active than those to the first (Fig. 2D).
Tactile stimuli to the head led to two types of rapid backward movement. First, from a horizontal position, the body moved backwards, collapsing progressively so that the abdomen came to rest on the ground with the head displaced from its original position by approximately half a body length. Second, the body height could be maintained so that the backward thrust of the legs launched the insect into a backwards jump.
To understand the movements underlying rapid jumping, high-speed images of the behaviour were captured and analysed.
Jumping
Both nymphs and adults jumped. Two movements appeared to contribute to a
forward jump; first, a forward and then a backward flick of the abdomen caused
by flexion at the joint between the meso- and metathoracic segments and at the
joint between the metathorax and the abdomen; second, extension of the
femoro-tibial joints and depression of the femora of the middle and hind legs.
In some jumps by adults, the wings were also unfurled and then flapped as the
insect launched into flight.
Before initiating a jump, the thorax and abdomen were held straight and horizontal with the weight of the body apparently supported largely by the middle and hind legs. The start of the jump was marked by the beginning of a forward curling of the abdomen and by initial movements of the femoro-tibial joints of the hind and middle legs. The abdomen was flicked forwards in 60-80 ms through angles of 80-90° by flexion at the joints between the meso- and metathorax and between the metathorax and abdomen. The femoro-tibial joints of the hind and middle legs were not fully flexed in preparation for jumping, and their starting angle was variable. Frequently, the front legs had no contact with the ground throughout a jump and were extended in front of the body (Fig. 3).
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In the jump of a nymph illustrated in Fig. 3, the initial movement was a flexion of the joint between the meso- and metathoracic segment, followed some 15 ms later by a flexion at the joint between the metathorax and the abdomen (Fig. 3A-C). The forward abdominal movement lasted 60 ms, during which the joint between the meso- and metathorax moved through 40° and that between the metathorax and abdomen moved through 35°, each joint reaching maximum angular velocities of 600 ° s-1. This resulted in the tip of the abdomen moving 32 mm dorsally relative to the joint with the metathorax and 57 mm relative to the ground at a linear velocity of 0.6 m s-1 and a maximum angular velocity of 2000 ° s-1. The abdomen reached its maximal forward excursion some 10 ms before the hind legs had extended fully and as the middle legs lost contact with the ground. It then reversed its motion as the body started to move forwards for the last 20 ms preceding take-off.
As the abdomen started to move forwards, the hind legs flexed at their femoro-tibial joints so that the body was lowered and moved backwards. This flexion of the hind legs could be due either to an active contraction of the leg muscles or to a passive reaction to the forces generated by the abdominal movement. The body does not, however, collapse onto the substratum, implying that some opposing force is generated by the legs. The tibia of the hind legs started to extend and the femora of the middle legs were depressed some 20 ms before the abdomen reversed direction. The body was lifted by as much as 10 mm or 77 % higher than the resting posture, as measured at the mesothoracic coxae 10 ms after the reversal of the abdominal movement. Complete extension of the femoro-tibial joint of a hind leg in the jump took 30 ms, with maximum angular velocities of 4000 ° s-1. The middle legs lost contact with the ground first, followed 10 and 30 ms later by the hind legs. The insect became airborne 80 ms after the initial abdominal movement with a take-off velocity of 0.8 m s-1. The mean acceleration during the jump was some 10 m s-2.
The translational kinetic energy (Ek) of the jump was
86 µJ, as given by the formula
Ek=mV2/2, where m is the body
mass in kg and V is the take-off velocity in m s-1.
Rotational kinetic energy was negligible since the insect did not spin once
airborne. The total energy required for the jump is the sum of
Ek at take-off and the potential energy
Ep due to height gain at take-off.
Ep=m1gh,
where m1 is the mass of body in kg (not including the legs
since these are still in contact with the ground), g is the
acceleration due to gravity and h is the height gained until
take-off. For this nymph, Ep10 µJ (assuming that 80
% of the body mass resides outside the legs), so that the total energy
required was approximately 96 µJ. The mean power output was estimated to be
almost 1 mW by taking the energy expenditure over the duration of the jump.
The trajectory of the body at take-off was almost parallel with the ground, so
that the displacement was away from the platform and then downwards.
Jumping performance in different animals
The mean time during which the body of either males or nymphs was
accelerated in jumping was 102±5 ms (mean ± S.E.M.,
N=18), measured from the first visible movement to when the insect
was airborne. The maximal excursion of the abdomen also varied in different
jumps, ranging from 65 ° (see Fig.
3) to 110 ° (see Fig.
5). Similarly, the femoro-tibial joints of the hind legs could
begin at a flexed angled or could be almost fully extended at an angle of 130
° (see Fig. 5). In
different jumps by the same or different insects, the movements of the
different legs were not always closely synchronised. For example, one tibia of
a pair of legs could extend before the other, and the hind legs could leave
the ground before the middle legs. Some insects could jump from a prone,
cataleptic posture in which they lay on the ground with the antennae, front
and middle legs extended forwards and parallel with the long axis of the body
and the hind legs extended backwards. From this position, the abdomen was
flicked forwards and the femora of the middle legs were depressed, resulting
in the body being raised and accelerated forwards. The hind legs were already
fully extended and did not appear to contribute to the movement.
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The mean take-off velocity in all nymphs and adult males analysed was 0.6±0.03 m s-1 (N=18), estimated as the mean velocity for the last 24 ms (six frames) before leaving ground. The angle of the anterior thorax relative to the horizontal just before take-off was 5±0.9 ° (N=16), and the take-off angle was low, ranging from 10 to 35 ° (means ± S.E.M., N=18). The forward and horizontal displacements of the body during a jump were usually no more than a few body lengths. Few jumps that were not assisted by wing movements led to a gain in height, but rather resulted in a dive from the platform away from the stimulus and, thereby resulting in a rapid displacement of a few body lengths away from a potentially threatening stimulus.
Jumping and abdominal movements
The movements of the abdomen and their relationship to the posture and
movement of the body were readily seen when individual points on the body were
plotted and superimposed on one image of an insect captured during a jump
(Fig. 4A). As the tip of the
abdomen moved upwards and forwards, the whole body moved backwards. This was
apparent as an initial backward movement of the joint between the metathorax
and abdomen and the joint between the meso- and metathorax and by the position
of the head. The legs sometimes flexed so that the initial movement of the
whole body was also slightly downwards in addition to backwards. As the
abdomen reached its most anterior position and slowed, the whole body began to
move forwards, and the velocity of this forward movement continued to increase
as the abdomen reversed its movement and moved backwards.
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Changes in the position of the centre of mass during a jump were calculated and superimposed on plots of the movements of the abdomen tip and the meso/metathoracic articulation (Fig. 4B). The calculation assumed that 80 % of the body mass was in parts of the body other than the legs (Fig. 1D,E) and took a weighted average of the positions of the main three body regions (the head plus pro- and mesothorax, the metathorax and the abdomen) during a jump. In the normal resting posture, the centre of mass lies posterior to the metathoracic coxae, approximately 12% along the length of the abdomen. As the abdomen was swung forwards between 140 and 50 ms before take-off, the position of the centre of mass also moved forwards and upwards so that it came to lie above and just behind the articulation of the mesothorax with the metathorax. The abdomen was then swung backwards so that for the last 40 ms before take-off the centre of mass moved backwards relative to the articulation between the meso- and metathorax. This means that, at take-off, the centre of mass was behind and just below the articulation between the meso- and metathorax. The insect did not spin when it became airborne, indicating that the forces at take-off were acting through the centre of mass.
Jumping and flying
Adult males jumped using characteristic abdominal flicking movements and
leg movements to launch themselves into flight
(Fig. 5A,B). The hind wings
began to open and elevate as the body first flexed at the joint between the
meso- and metathorax. The elevation continued as the abdomen was thrust
forwards by a 70° flexion at the joint between the metathorax and abdomen
that lasted 60 ms at a maximum angular velocity of 1800° s-1,
and with the tip of the abdomen moving at a linear velocity of 0.9
ms-1. During this time, the femoro-tibial joint of one of the hind
legs, having started from an initial angle of 130°, extended by only a
further 20° before this leg lost contact with the ground. Both hind legs
left the ground before the wings reached their most elevated position. The
wings then started to depress, the abdomen reversed its direction to move
backwards and one of the middle legs lost contact with the ground. When wing
depression was complete, the other middle leg lost contact with the ground,
and the insect became airborne 150 ms after the start of all these movements
with a take-off velocity of 0.6 m s-1 and at a shallow take-off
angle of 10°. The translational kinetic energy of the jump was 25 µJ.
Repetitive flapping of the wings at a frequency of approximately 14-15 Hz
enabled the insect to continue gaining height. In jumps by males that were
wing-assisted in this way and led directly to flapping flight, the result was
a gain in height; in the larger and heavier females, the trajectory was
downwards, even though the wings were flapped. In the wing-assisted jumps
analysed, the angle of the anterior thorax relative to the horizontal just
before take-off and when the wings were fully elevated was 7±1.6°
(mean ± S.E.M., N=9) and was therefore similar to that in
jumps that did not involve the wings.
Take-off and flying without jumping
Adult males could take off and fly without launching themselves by jumping
(Fig. 6A-C). The first movement
was elevation of the hind wings, and it was only when this was half-completed
that the tibiae of the hind legs began to extend. As the hind wings were
elevated further, the femora of the middle legs were depressed, the tibiae
were extended and the body was elevated further. No movements of the abdomen
occurred until the wings began to depress. No change occurred in the angle
between the meso- and metathorax, but a flexion at the joint between the
metathorax and abdomen resulted in a small dorsal curvature replacing the
formerly ventral curve. This curvature increased until midway through the
second cycle of wing elevation, when the tibial extension of the hind legs was
also completed and the insect became airborne. In the example shown, take-off
velocity was 0.9 m s-1, and the continued flapping of the wings
enabled the insect to gain height. The angle of the anterior thorax relative
to the horizontal just before take-off and when the wings were fully elevated,
was much greater at 28±2.6° (mean ± S.E.M., N=10)
in take-offs into flight in which jumping was not involved than in jumps alone
or in jumps accompanied by flapping wing movements.
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Backward evasive movements
If, while standing on a horizontal surface, a stick insect was touched
lightly on the head, the anterior part of the body or the front legs, it
rapidly moved away from the stimulus (Figs
7,
8). These backward movements by
nymphs and males lasted 88±5.9 ms and propelled the insect backwards by
33±3.4 mm at velocities of 0.4±0.2 m s-1 (means
± S.E.M., N=21). The movements did not involve flicking
movements of the abdomen. The response most frequently observed was a backward
movement combined with the body collapsing onto the substratum
(Fig. 7A,B). During these
movements, the thorax and abdomen remained in their initial posture
throughout, but the angles of the hind femora with the body decreased so that
the hind legs were rotated forwards as the body height decreased. The
femoro-tibial angle of the hind legs also decreased so that the flexion
movement appeared to pull the insect backwards. Rotation of the middle legs
also accompanied these movements. The height of the body from the substratum
decreased throughout these legs movements so that, eventually, it came to lie
with the abdomen prostrate. The net result was to displace the head from its
original position backwards by approximately half a body length, with the head
moving downwards.
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Some movements from the same initial posture launched the insect into a backward jump from the platform with a consequent greater displacement (Fig. 8A). Similar sequences of leg movements occurred in such movements, but the body was not lowered. The propulsion was insufficient to elevate the body so, when the legs lost contact, the insect started to fall, often bumping into the edge of the platform on its backward and downward path.
The same backward darting movements also occurred from cataleptic postures when the body was prostrate and with the legs held parallel to the long axis of the body (Fig. 8B). The first movements were a rotation of the hind legs so that they were raised and moved forward by a rotation at the joint with the thorax. The tibiae of the hind legs were then flexed at their joints with the femora, and the body moved backwards. The joint between the meso- and metathorax was also flexed so that the anterior thorax and head were raised and supported by the middle legs.
Jumping from a vertical posture
When standing vertically on a twig or a pillar with the head up, stick
insects produced two types of movement that paralleled those shown from a
horizontal posture. In response to a stimulus to the abdomen from below
(N=26), they jumped upwards and outwards from the pillar before
falling backwards to the ground (Fig.
9). When stimulated on the head from above (N=14), they
pushed backwards and fell straight down from the pillar
(Fig. 10B).
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The upward jumping movements had all the characteristics of jumps from a horizontal posture. The abdomen was curled dorsally (upwards) by flexions at the joints between the meso- and metathorax and between the metathorax and the abdomen. At the same time, the femoro-tibial joints of the hind legs were extended. The whole body moved upwards and continued to do so even when the hind legs lost contact with the pillar. The dorsal movements of the abdomen then slowed and reversed and, some 40 ms after the hind legs had left the pillar, the middle legs also lost contact so that the insect became airborne. The jump propelled the insect laterally and allowed it to fall a few body lengths horizontally away from the original perch. The horizontal displacement could be increased when the jump was accompanied by flapping flight, but rarely resulted in a gain in height (Fig. 10A).
The backward falling movements also had the characteristics of the backward movements from a horizontal position in that neither abdominal nor wing movements contributed (Fig. 10B). The middle and hind legs pushed downwards and then lost contact with the pillar so that the head moved closer to the pillar as the insect fell. At the end of its fall, the insect was now much closer to the base of the pillar than when the abdomen had been flicked upwards and backwards or when the wing movements were also used.
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Discussion |
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Body design for jumping
The body shape of Sipyloidea is typical of stick insects in that
it is long and thin with long thin legs and long antennae. Movements of the
abdomen and the hind and middle legs are involved in jumping. The adult female
abdomen accounts for 44 % of the body mass and the adult male abdomen for 35
%, exceeding by many times the mass of the legs. This contrasts with the body
design of a locust, in which the abdomen comprises just 28 % of the total body
mass. The abdomen of Sipyloidea can be flexed at the joint with the
metathorax, which in turn can be flexed at its joint with the mesothorax.
These movements, together with movements at the abdominal segments, allow the
abdomen to be curled forwards by as much as 80-90°, so that its tip comes
to lie vertically above the metathorax. The forces generated by the rhythmic
dorsal and ventral flexion movements of the abdomen during struggling can be
much greater than the body weight. During a jump, the abdomen is first curled
forwards and then straightened in a backward movement, thereby increasing the
forces transmitted to the ground through the tarsi of the middle and hind
legs. Once airborne, these forces would cause the insect to rotate, but the
movements of the abdomen also change the position of the centre of mass. The
abdominal movements would therefore appear to have two actions. First, they
add momentum to the jump. Second, they allow the forces at take-off to act
through the centre of mass of the body and ensure that the body does not spin
when airborne.
The legs alone do not appear to be responsible for generating all the
forces needed in jumping for three reasons. First, all three pairs of legs are
of similar length so that they resemble the legs of non-jumping stick insects
such as Carausius. The design of the legs is different, therefore,
from that of powerful jumping orthopterans such as the locust, which have
large hind legs that are much longer than the other two pairs of legs, so that
the ratio of leg length is (front:middle:hind) 1:1.3:3.2. Even the false stick
insect Prosarthria teretrirostris (an orthopteran), which jumps
powerfully despite having spindly legs, has long hind legs and a leg length
ratio in females of 1:1:2.6 (Burrows and
Wolf, 2002). The thin femora of the hind legs of
Sipyloidea suggest that they do not contain muscles powerful enough
to launch the body into a jump. Furthermore, the front legs often do not
support the body weight and in many jumps are not in contact with the
ground.
Second, the femoro-tibial joints of the hind legs have no specialisations
that would allow the slow development of force by the extensor muscles, the
storage of energy and then the sudden release of this energy to power the
jump. This again contrasts with the design of this joint in locusts
(Bennet-Clark, 1975;
Burrows and Morris, 2001
;
Heitler, 1974
).
Third, before a jump, the tibiae of the hind legs are not fully flexed about the femora and often start at a position that allows only a few degrees of further extension. The large variation in the initial starting angles of the femoro-tibial joints suggests that the force contributed to the jump is also variable. Depression of the femora and extension of the tibiae of the meso- and metathoracic legs may nevertheless contribute to the jump by raising the body from the ground and shifting its angle of attack. In backward evasive movements, in which the abdomen is not curled, the legs provide the only thrust.
In nymphs, which have no wings, the abdominal and leg movements are the
only means of generating the forces for a jump. In adults, the front wings are
scarcely more than stubs, but the large hind wings can be opened and flapped
to generate lift and thrust. Even in adults, however, many jumps are produced
without the assistance of the wings. When they are used, the wings are opened
at the same time as the abdomen is thrown forward and then depressed as the
abdomen swings backwards so that flapping flight assists the jump. Adult males
can gain height from such a wing-assisted takeoff, but the heavier females
still lose height. Use of the wings may nevertheless provide greater stability
during a jump, as it does for flea-beetles when they use their wings
(Brackenbury and Wang,
1995).
Jumping mechanisms in other animals
Locusts (Bennet-Clark,
1975), false stick insects
(Burrows and Wolf, 2002
) and
fleas (Bennet-Clark and Lucey,
1967
) all use rapid extension of the hind legs to propel their
jump. Male locusts weighing 1.5-2.0 g can take off in 25-30 ms at velocities
of 3.2 m s-1 and at peak accelerations of 180 m s-2 to
jump a distance of 0.8-0.95 m (20 body lengths). The energy required can be as
great as 11 mJ and is generated by muscle contraction in advance of the jump
and stored in cuticular deformations. Male false stick insects
(Prosarthria) weigh only 0.28 g and take off in 30 ms at velocities
of 2.5-3.0 m s-1 and at peak accelerations of 165 m s-2
to jump a distance of 0.9 m (13 body lengths)
(Burrows and Wolf, 2002
).
Again, the energy requirement of 850 µJ can be met only by muscle
contraction in advance of the jump, but is achieved without bending of the
semi-lunar processes that provide almost half the energy storage for the
locust. The flea Spilopsyllus cuniculus weighs only 0.45 mg and can
jump 3-5 cm into the air at a take-off velocity of approximately 1 m
s-1. The energy required is again produced by a prior contraction
of the enlarged depressor muscle in the hind leg and then stored in a pad of
resilin. The stored force is released suddenly by the contraction of a small
muscle that changes the point of action of the depressor muscle so that the
femur can be depressed rapidly.
In contrast to these performances, the jumping of Sipyloidea is
much more modest. The time during which the insect is accelerated in a jump is
almost three times as long as in a locust, and the take-off velocities,
acceleration and energy requirements are much smaller. Our estimate of 1 mW
for the mean power output during a jump is well within the bounds of direct
muscle action (Weis-Fogh and Alexander,
1977), so that there is no need to invoke storage mechanisms to
power the jump, as in many other jumping insects. This stick insect combines
the kinetic energy provided by abdominal movements with the forces generated
by two pairs of legs, thereby extending the time over which the acceleration
is applied. In these respects, it has features in common with jumping spiders
and jumping ants.
The salticid spider Sitticus pubescens jumps a distance of some 7
cm or up to 10 body lengths at a take-off velocity of approximately 0.7 m
s-1 (Parry and Brown,
1959). The thrust for the jump is provided mainly by the fourth
pairs of legs, which are extended fully by depression of the femur and
extension at the femur/patella joint. The third pair of legs extends by only a
small amount before the legs lose contact with the ground, and the first two
pairs of legs are lifted from the ground before the jump even starts. Other
jumping spiders may use the simultaneous extension of two pairs of legs. The
ant Harpegnathos saltator jumps to escape from predators and to hunt
prey by the rapid extension of both the middle and hind pairs of legs
(Baroni et al., 1994
;
Tautz et al., 1994
). The jump,
which takes some 15-25 ms from the time the head is first raised to when the
legs leave the ground, propels the body forwards some 3-4 cm at an angle of
approximately 40 °, but with a low take-off velocity of 0.6-0.7 m
s-1. The centre of mass of these ants is anterior to the
mesothoracic legs so that the body does not spin during a jump. In
Gigantiops destructor, however, it is behind the hind legs and, to
compensate, the gaster (part of the abdomen) is moved forwards at the same
time as the legs are extended and is held in the forward position as it
becomes airborne. As in Sipyloidea, the abdominal movements may also
provide kinetic energy to propel the body forward
(Tautz et al., 1994
).
Lines of defence
How effective behaviourally is the jumping of Sipyloidea? Broadly,
two main strategies are used to avoid predation: first, it adopts cryptic
postures to minimise detection and, second, it moves away from potentially
harmful stimulation. Its cryptic body shape and coloration, helped by an
ability to sustain a particular posture for a long time without moving, make
it hard for potential predators to detect. Tactile stimulation leads to a
number of behavioural responses. First, it may withdraw rapidly from a
stimulus and then freeze, so that the predator may lose contact and then has
to go through the recognition process again. Second, it may walk rapidly away,
so that the predator has to pursue it. Third, it may jump from its perch, thus
propelling itself quickly and some distance from the predator to land amongst
the leaf litter, where its cryptic posture and coloration will again make it
difficult to detect. Use of the abdomen to provide forward or upward momentum,
depending on the initial starting posture when jumping, may have evolved from
the abdominal curling movements seen in defensive postures by other stick
insects. Finally, the jump may be combined with flapping flight to put a large
distance between the insect and the predator, making pursuit possible only for
aerial predators. The ability to jump rapidly, if only for short horizontal
distances, could therefore be an important survival strategy.
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References |
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Baroni, U. C., Boyan, G. S., Blarer, A., Billen, J. and Musthak, A. T. M. (1994). A novel mechanism for jumping in the Indian ant Harpegnathos saltator (Jerdon) (Formicidae, Ponerinae). Experientia 50,63 -71.
Bassler, U. (1983). The neural basis of catalepsy in the stick insect Cuniculina impigra. III. Characteristics of the extensor motor neurons. Biol. Cybern. 46,159 -165.
Bassler, U. and Foth, E. (1982). The neural basis of catalepsy in the stick insect Cuniculina impigra. I. Catalepsy as a characteristic of the femurtibia control system. Biol. Cybern. 45,101 -105.
Bassler, U., Storrer, J. and Saxer, K. (1982). The neural basis of catalepsy in the stick insect Cuniculina impigra. II. The role of the extensor motor neurons and the characteristics of the extensor tibiae muscle. Biol. Cybern. 46, 1-6.
Bedford, G. O. (1976). Defensive behaviour of the New Guinea stick insect Eurycantha. Proc. Linn. Soc. NSW 100,218 -222.
Bedford, G. O. (1978). Biology and ecology of the Phasmatodea. Annu. Rev. Entomol. 23,125 -149.
Bedford, G. O. and Chinnick, L. J. (1966). Conspicuous displays in two species of Australian stick insects. Anim. Behav. 14,518 -521.[Medline]
Bennet-Clark, H. C. (1975). The energetics of the jump of the locust Schistocerca gregaria. J. Exp. Biol. 63,53 -83.[Abstract]
Bennet-Clark, H. C. and Lucey, E. C. A. (1967). The jump of the flea: a study of the energetics and a model of the mechanism. J. Exp. Biol. 47,59 -76.[Medline]
Brackenbury, J. and Hunt, H. (1993). Jumping in springtails: mechanism and dynamics. J. Zool., Lond. 229,217 -236.
Brackenbury, J. and Wang, R. (1995). Ballistics
and visual targeting in flea-beetles (Alticinae). J. Exp.
Biol. 198,1931
-1942.
Brown, R. H. J. (1967). The mechanism of locust jumping. Nature 214,939 .[Medline]
Burrows, M. and Morris, G. (2001). The
kinematics and neural control of high-speed kicking movements in the locust.
J. Exp. Biol. 204,3471
-3481.
Burrows, M. and Wolf, H. (2002). Jumping and
kicking in the false stick insect Prosarthria: kinematics and neural
control. J. Exp. Biol.
205,1519
-1530.
Driesang, R. B. and Büschges, A. (1993). The neural basis of catalepsy in the stick insect. IV. Properties of nonspiking interneurons. J. Comp. Physiol. A 173,445 -454.
Eisner, T. (1965). Defensive spray of a phasmid insect. Science 148,966 -968.
Evans, M. E. G. (1972). The jump of the click beetle (Coleoptera: Elateridae) a preliminary study. J. Zool., Lond. 167,319 -336.
Evans, M. E. G. (1973). The jump of the click beetle (Coleoptera, Elateridae) energetics and mechanics. J. Zool., Lond. 169,181 -194.
Godden, D. H. (1974). The physiological mechanism of catalepsy in the stick insect Carausius morosus Br. J. Comp. Physiol. 89,251 -274.
Heitler, W. J. (1974). The locust jump. Specialisations of the metathoracic femoraltibial joint. J. Comp. Physiol. 89,93 -104.
Henry, G. M. (1922). Stridulation in the leaf insect. Spolia Zeylan 12,217 -219.
Parry, D. A. and Brown, R. H. J. (1959). The jumping mechanism of salticid spiders. J. Exp. Biol. 36,654 -664.
Rehn, J. A. G. (1957). The description of the female sex of Pterinoxylus spinulosus with notes on stridulation in the female sex of this genus. Trans. Am. Entomol. Soc. 83,185 -194.
Robinson, M. H. (1968a). The defensive behaviour of the Javanese stick insect Orxines macklotti with a note on the startle display of Metriotes diocles Westw. (Phasmatodea, Phasmidae). Entomol. Mon. Mag. 104, 46-56.
Robinson, M. H. (1968b). The defensive behaviour of the stick insect Oncotophasma martini (Griffini) (Orthoptera: Phasmatidae). Proc. R. Ent. Soc. Lond. 43,183 -187.
Robinson, M. H. (1969). The defensive behaviour of some orthopteroid insects from Panama. Trans. R. Ent. Soc. Lond. 121,281 -303.
Rothschild, M., Schlein, Y., Parker, K. and Sternberg, S. (1972). Jump of the oriental rat flea Xenopsylla cheopsis (Roths.). Nature 239, 45-47.
Tautz, J., Holldobler, B. and Danker, T. (1994). The ants that jump: different techniques to take off. Zoology 98,1 -6.
Weis-Fogh, T. and Alexander, R. McN. (1977). The sustained power output from straited muscle. In Scale Effects in Animal Locomotion (ed. T. J. Pedley), pp.511 -525. London: Academic Press.