The castoff skin nearby is a dead giveaway to enemies so the nymph quickly consumes the shriveled exoskeleton to get rid of the evidence, simultaneously recycling the protein it took to create the discarded layer at the same time.
Stick insects aren't venomous but if threatened, one will use whatever means necessary to thwart its attacker. Some will regurgitate a nasty substance to put a bad taste in a hungry predator's mouth. Others reflex bleed, oozing a foul-smelling hemolymph from joints in their body. Some of the large, tropical stick insects may use their leg spines, which help them climb, to inflict some pain on an enemy.
Stick insects may even direct a chemical spray, much like tear gas, at the offender. Stick insect eggs that resemble hard seeds have a special, fatty capsule called a capitulum at one end. Ants enjoy the nutritional boost provided by the capitulum and carry the stick insect eggs back to their nests for a meal. After the ants feed on the fats and nutrients, they toss the eggs onto their garbage heap, where the eggs continue to incubate, safe from predators.
As the nymphs hatch, they make their way out of the ant nest. Some stick insects can change color, like a chameleon, depending on the background where they're at rest. Stick insects may also wear bright colors on their wings but keep these flamboyant features tucked away. When a bird or other predator approaches, the stick insect flashes its vibrant wings, then hides them again, leaving the predator confused and unable to relocate its target.
When all else fails, play dead, right? A threatened stick insect will abruptly drop from wherever it's perched, fall to the ground, and stay very still. This behavior, called thanatosis , can successfully discourage predators. A bird or mouse may be unable to find the immobile insect on the ground or prefer living prey and move on.
In , a newly discovered stick insect species from Borneo broke the record for longest insect which had previously been held by another stick insect, Pharnacia serratipes. The Chan's Megastick, Phobaeticus chani , measures an incredible 22 inches with legs extended, with a body length of 14 inches. Shelomi, Matan, and Dirk Zeuss.
Actively scan device characteristics for identification. Use precise geolocation data. If the swaying behavior of animals is a form of camouflage, then it must necessarily generate movements consistent with those of surrounding vegetation. To our knowledge, only Fleishman , has quantified and compared animal and plant movements in this way, and this was limited to a single animal.
We investigate this behavior in quantitative detail using the stick insect E. This phytophagous, sexually dimorphic phasmatid is found in the rainforests of tropical and subtropical Queensland and northern New South Wales, Australia Gurney ; Brock and Hasenpusch The eggs of E.
Females may live up to 18 months after maturation, whereas males live 3—6 months after maturation Schneider and Elgar The primary predators of adult phasmatids are birds, which search forest canopies for insects hanging in the trees Readshaw Our first objective in the present study was to confirm that wind is a sufficient cue to stimulate swaying behavior, after which we examined how insect swaying behavior is influenced by variation in wind.
We subsequently explored the behavior in more detail through quantitative measurements of both insect and plant swaying movements under the same natural conditions.
In this study, we combined simple observational measures of behavior with quantitative analyses of swaying from 3D reconstructions of movement. Subjects were drawn from a stock population of female E.
Individuals were fed with fresh leaves from locally sourced trees Eucalypt sp. Our first experiment was designed to test the prediction that E. Thirteen adult average weight The resting time before and between treatments ensured that insects returned to hanging in their natural position and to reduce the production of chemical secretions associated with stress Carlberg The cameras were calibrated using direct linear transformation DLT following Hedrick Briefly, this involved placing a transparent plastic container with 60 noncoplanar points distributed evenly throughout the volume of the object.
The calibration object was placed such that all points could be located in images from both cameras. Still images of the object, one from each camera view, were loaded into Matlab MathWorks Inc. These points, along with a text file containing the known position in 3D space of the 60 points, are then used to calculate a series of coefficients that specifies how points in space are projected onto a 2D image plane.
Footage of insect movement from each camera was subsequently read into Matlab, and the position of the tip of the lower abdomen was then located in every frame from both camera views. The position of the tip could then be reconstructed in 3D using the x — y coordinate data from both cameras along with the DLT calibration coefficients.
We first measured the volume of 3D space swept by the tip of the abdomen of each insect Figure 2a by calculating the 3D convex hull of position data in Matlab. Furthermore, as perceived movement depends on viewing position, we also calculated sweep area 2D convex hull as if viewed from side on, above, and front on to the insect Figure 1c. Calculation of sweep area from different viewing positions necessarily reduces the data to 2 coordinates instead of 3 Figure 2b.
We compared the 3D sweep area of insect movements in wind and no wind conditions with a linear mixed effects model in the R statistical environment R Development Core Team Treatment wind or no wind was set as a fixed effect and insect identity as a random effect to account for repeat observations of the same insect, using the lmer function from the lme4 package Bates et al.
Two-dimensional sweep area was considered in the same way, but included viewing position front, above, side as a second fixed effect. Representative data from 1 insect during the wind-present and wind-absent trials. Each displacement profile was split into 8 partially overlapping epochs gray lines and averaged black line.
To quantify the swinging movement of the insect, we calculated the Euclidean distance between the xyz coordinates of the tip of the abdomen in each frame relative to its position at the start of the sequence. In so doing, we defined displacement—time profiles for each session Figure 2c.
We used the spectrogram function in Matlab that splits the signal into 8 partially overlapping epochs and analyses them separately, after which we calculated the average Figure 2d.
Displacement—time profiles in 2D were also determined for each viewing position and subjected to FFT analysis as described above. Frequency spectra were visually inspected, while swaying movements were more formally compared by calculating signal power as the root mean square of displacement profiles and compared using linear mixed effects models.
We investigated whether the nature of prevailing wind influenced the swaying behavior in E. Wind speed is unlikely to stay constant in nature and insects are likely to adjust their behavior accordingly. Consequently, we predicted that the insects would exhibit measurable differences in swaying behavior in variable wind relative to constant wind. Thirty-two adult females were allocated randomly into 2 treatment groups featuring either constant or variable wind using a household pedestal fan.
In the constant wind treatment, individuals were subjected to 5min of continuous, constant wind speed 2. In each treatment, individual E. All trials were recorded using a Panasonic HDC-SD80 Full HD Camcorder camera and an observer, who was done blind to the treatment, counted the number of swaying cycles in each successive minute for both treatments.
We compared swaying frequency within each of the five 1-min time periods in the R statistical environment R Development Core Team We constructed a linear mixed effects model using the lmer function from the lme4 package, setting wind condition constant or variable and time 5 time bins as fixed factors and used insect identity as a random factor. Pairwise comparisons were undertaken using the difflsmean function from the lmerTest package Kuznetsova et al.
Our final experiment considered whether insect movement is consistent with the movement of wind-blown plants. Insects were placed on the stem of a potted Eucalytpus gregsoniana tree that was surrounded by 2 potted E. The stem of the E. We used the same approach to filming as described above, positioning 2 cameras perpendicular to each other but with a clear line-of-sight to the insect.
The insects were left for 5min to acclimate before filming commenced and filming ceased after 10min. Ten insects were used in this part of the study. We observed 3 different scenarios within each trial: no insect movement and no noticeable plant movement, plant movement but no insect movement, and simultaneous insect and plant movement. We chose to focus on the latter 2 scenarios and randomly selected an 8-s sample of both scenarios from each insect for further analysis.
We also tracked the movement of the host and surrounding plants. Prior to the experiment, crosses were drawn on the leaves of plants so that they could be reliably tracked on video and to ensure that the same part of the plant was tracked in successive frames. Four points on the host plant and one each on the surrounding plants were randomly selected with the only constraint being that they were visible from both camera views.
Our approach enabled us to quantify plant motion that would likely be seen by a predator scanning the scene and simultaneously with a swaying insect. To compare insect and plant movement, we examined log—log plots of insect and plant movement Figure 2e and compared signal power using the linear mixed effects model described above and setting fixed factors of object insect, plant , scenario insect moved, insect stationary , and viewing position top, front, side , along with insect identity as a random effect.
Pairwise comparisons were undertaken using the difflsmean function from the lmerTest package. Our observations suggest that female E. The frequency spectra shown in Figure 4 indicate similarities in frequency peaks but clear differences in amplitudes.
In each example, the view from front on generated larger amplitudes than the other 2 viewpoints. Power spectral density for insect swaying movements when viewed from different viewing positions: viewed from front on and along the length of the insect solid line , from side on dotted line , and from above dashed line.
Representative plots from 4 insects are shown during wind trials of experiment 1. Although swaying is triggered by wind, the nature of the wind stimulus exerts an important effect on swaying behavior Figure 5. We explored the interaction in more detail by comparing between wind treatments within each block of time.
Log—log plots of the trials in which insects and plants were both moving show that the movement of swaying E. Not surprisingly, the trials in which insects did not move revealed how different the insect might appear when surrounded by swaying plants Figure 7. We explored the insect—plant trials further by considering signal power from the different viewpoints. Log—log plots of frequency and amplitude for trials in which plants moved in response to wind and the insects swayed. Log—log plots of frequency and amplitude for trials in which plants moved in response to wind, but the insects did not sway.
Wind alone appears to be sufficient to trigger swaying motion in E. However, wind per se does not maintain this behavior, as the insects significantly decreased the number of sways under constant wind relative to variable wind conditions. One explanation for the observed reduction in swaying behavior in the present study is that insects might be habituated to the constant unchanging stimulus and a secondary stimulus or cue might be needed to prolong this behavior.
Also, if there were an energetic cost associated with generating sways then a mechanism that helps to limit the activity seems likely. It is intriguing to consider the possibility that insects pay close attention to environmental conditions and adjust their behavior accordingly. The results of the final experiment comparing insect and plant movements are consistent with this view, where it is possible that the insects perceived the conditions to be unsuitable and ceased swaying.
Although this might be necessary to ensure they are not blown off the plant, it is also possible that insects are unable to match the frequency of leaf movements under strong wind conditions. This is particularly important from a motion vision perspective, as movement that is atypical to plant motion will be highly conspicuous Fleishman ; Peters et al. These non-mutually exclusive explanations require further investigations.
Nevertheless, in circumstances when plant motion was not too strong, the movement of insects in the frequency domain is performed in a manner that is consistent with the movement of wind-blown plants. Variable wind conditions are likely to create highly fluctuating plant motion patterns across different species of plant due to the differences in shape and mechanical properties of the leaf and branches, leaf density, stem thickness, and height above ground Hannah et al. Therefore, the effectiveness of this motion matching should not require that they precisely replicate the motion of a given plant.
Therefore, we would not expect a perfect motion overlap between the insect and the background plants; the results from one particular plant type may not necessarily emerge in others. Motion matching is not the only defense against predators utilized by E.
Other adaptations include body armor covered with spikes, the production of alarm chemicals that deters predators, and the cryptic coloration of a senescing leaf Carlberg ; Dossey et al. Nonetheless, at times when the insect swayed along with the plants, the frequency domain of the sway motion laid within the frequency range of the plant motion, which might suggest a relatively good motion match between the insect and its surrounding plants Figure 5.
Our methodological approach allowed us to reconstruct the movement of insects and plants in 3D so that we can quantify how the insect or plant moved in space. However, this approach does not take into account that movements in 3D space are effectively projected onto 2D during the early stages of vision, which means that movements in and out of this virtual 2D plane will not be fully represented.
Our characterization of sweep area from different viewpoints in experiment 1 quantified this variation Figure 3b. Frequency analysis showed that the same physical movements could indeed generate different signals from different viewpoints Figure 4 , although the variation between viewpoints was predominantly in terms of amplitudes, as frequency profiles corresponded reasonably well.
The front on view consistently produced the largest amplitudes, but interestingly, the relative amplitudes of the other 2 viewpoints were not as consistent. Our analysis of the effect of viewing position on this behavior is preliminary but certainly warrants further consideration.
Of particular interest is whether this variability affects the effectiveness of the motion matching behavior. Our investigation provides compelling evidence that the swaying behavior of E.
The next step is to determine whether this translates into a survival advantage for these insects. If so, it would be then necessary to determine the mechanism that achieves this. Does the similarity in insect and plant motion prevent detection motion crypsis or promote misclassification by the predator motion masquerade?
Put your hand or a piece of paper in front of its path and let it crawl aboard. Return it to the branch of a nearby tree. Stick Insects Go Back. What do stick insects look like? Where are stick insects found? Fast facts: The stick insect is a Phasmid — insects that eat leaves and resemble leaves or sticks.
The female stick insect can reproduce year-round and without fertilisation. This means that she can deposit her eggs and have them grow into normal, healthy nymphs without ever needing to find a mate. Stick Insects — the full story Somewhere amongst the leaves in your backyard is a camouflage master. Did you know? Tip Look for stick insects when pruning or removing dropped branches from your backyard.
Tips to help Backyard Buddies.
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