̽��ֱ�� of Cambridge - Gregory Sutton

Baby mantises harness mid-air ‘spin’ during jumps for precision landings

fpjl2 — Thu, 05 Mar 2015 16:48:31 +0000

̽��ֱ��smaller you are, the harder it is not to spin out of control when you jump. Miniscule errors in propulsive force relative to the centre of mass results in most jumping insects – such as fleas, leafhoppers and grasshoppers – spinning uncontrollably when they jump.

Until now, scientists worked under the hypothesis that such insects can’t control this, and spin unpredictably with frequent crash landings.

But new high-speed video analysis of the jumps of wingless, baby praying mantises has revealed a technique which actually harnesses the spinning motion, enabling them to jump with accuracy at the same time as repositioning their body mid-air to match the intended target – all in under a tenth of a second.

Researchers used a thin black rod distant from the platform on which the mantises sat as a target for them to jump at.

During the jumps, the insects rotated their legs and abdomen simultaneously yet in varying directions – shifting clockwise and anti-clockwise rotations between these body parts in mid-air – to control the angular momentum, or ‘spin’. This allowed them to shift their body in the air to align themselves precisely with the target on which they chose to land.

And the mantises did all of this at phenomenal speed. An entire jump, from take-off to landing, lasted around 80 milliseconds – literally faster than the blink of a human eye.

At first, scientists believed the mantis had simply evolved a way to mitigate the natural spin that occurs when such small insects jump at speed.

On closer inspection, however, they realised the mantis is in fact deliberately injecting controlled spin into the jump at the point of take-off, then manipulating this angular momentum while airborne through intricate rotations of its extremities in order to reposition the body in mid-air, so that it grasps the target with extreme precision.

For the study, published today in the journal Current Biology, the researchers analysed a total of 381 slowed-down videos of 58 young mantises jumping to the target, allowing them to work out the intricate mechanics used to land the right way up and on target virtually every time.

“We had assumed spin was bad, but we were wrong – juvenile mantises deliberately create spin and harness it in mid-air to rotate their bodies to land on a target,” said study author Professor Malcolm Burrows from Cambridge ̽��ֱ��’s Department of Zoology, who conducted the research with Dr Gregory Sutton from Bristol ̽��ֱ��.

“As far as we can tell, these insects are controlling every step of the jump. There is no uncontrolled step followed by compensation, which is what we initially thought,” he said.

In fact, when the researchers moved the target closer, the mantises spun themselves twice as fast to ensure they got their bodies parallel with the target when they grasped it.

For Sutton, the study is similar to accountancy, only with distribution of momentum instead of money. “ ̽��ֱ��mantis gives itself an amount of angular momentum at take-off and then distributes this momentum while in mid-air: a certain amount in the front leg at one point; a certain amount in the abdomen at another – which both stabilise the body and shift its orientation, allowing it to reach the target at the right angle to grab on,” he said.

̽��ֱ��researchers tested what would happen if they restricted the ability of the mantis to harness and spread the ‘spin’ to its extremities during a jump. To do this, they glued the segments of the abdomen together, expecting the mantis to spin out of control.

Intriguingly, the accuracy of the jump wasn’t impeded. ̽��ֱ��mantises still reached the target, but couldn’t rotate their bodies into the correct position – so crashed headlong into it and bounced off again.

̽��ֱ��next big question for the researchers is to understand how the mantis achieves its mid-air acrobatics at such extraordinary speeds. “We can see the mantis performs a scanning movement with its head before a jump. Is it predicting everything in advance or does it make corrections at lightning speed as it goes through the jump? We don’t know the answer between these extreme possibilities,” said Burrows.

Sutton added: “We now have a good understanding of the physics and biomechanics of these precise aerial acrobatics. But because the movements are so quick, we need to understand the role the brain is playing in their control once the movements are underway.”

Sutton believes that the field of robotics could learn lessons from the juvenile mantis. “For small robots, flying is energetically expensive, and walking is slow. Jumping makes sense – but controlling the spin in jumping robots is an almost intractable problem. ̽��ֱ��juvenile mantis is a natural example of a mechanical set-up that could solve this,” he said.

Professor Malcolm Burrows and Dr Gregory Sutton

High-speed videos reveal that, unlike other jumping insects, the juvenile praying mantis does not spin out of control when airborne. In fact, it both creates and controls angular momentum at extraordinary speeds to orient its body for precise landings.

As far as we can tell, these insects are controlling every step of the jump

Malcolm Burrows

Malcolm Burrows and Greg Sutton

A juvenile praying mantis

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Functioning ‘mechanical gears’ seen in nature for the first time

fpjl2 — Thu, 12 Sep 2013 18:05:28 +0000

̽��ֱ��juvenile Issus - a plant-hopping insect found in gardens across Europe - has hind-leg joints with curved cog-like strips of opposing ‘teeth’ that intermesh, rotating like mechanical gears to synchronise the animal’s legs when it launches into a jump.

̽��ֱ��finding demonstrates that gear mechanisms previously thought to be solely man-made have an evolutionary precedent. Scientists say this is the “first observation of mechanical gearing in a biological structure”.

Through a combination of anatomical analysis and high-speed video capture of normal Issus movements, scientists from the ̽��ֱ�� of Cambridge have been able to reveal these functioning natural gears for the first time. ̽��ֱ��findings are reported in the latest issue of the journal Science.

̽��ֱ��gears in the Issus hind-leg bear remarkable engineering resemblance to those found on every bicycle and inside every car gear-box. Each gear tooth has a rounded corner at the point it connects to the gear strip; a feature identical to man-made gears such as bike gears – essentially a shock-absorbing mechanism to stop teeth from shearing off.

̽��ֱ��gear teeth on the opposing hind-legs lock together like those in a car gear-box, ensuring almost complete synchronicity in leg movement - the legs always move within 30 ‘microseconds’ of each other, with one microsecond equal to a millionth of a second.

This is critical for the powerful jumps that are this insect’s primary mode of transport, as even miniscule discrepancies in synchronisation between the velocities of its legs at the point of propulsion would result in “yaw rotation” - causing the Issus to spin hopelessly out of control.

“This precise synchronisation would be impossible to achieve through a nervous system, as neural impulses would take far too long for the extraordinarily tight coordination required,” said lead author Professor Malcolm Burrows, from Cambridge’s Department of Zoology.

“By developing mechanical gears, the Issus can just send nerve signals to its muscles to produce roughly the same amount of force - then if one leg starts to propel the jump the gears will interlock, creating absolute synchrony.

“In Issus, the skeleton is used to solve a complex problem that the brain and nervous system can’t,” said Burrows. “This emphasises the importance of considering the properties of the skeleton in how movement is produced.”

"We usually think of gears as something that we see in human designed machinery, but we've found that that is only because we didn't look hard enough,” added co-author Gregory Sutton, now at the ̽��ֱ�� of Bristol.

“These gears are not designed; they are evolved - representing high speed and precision machinery evolved for synchronisation in the animal world.”

Interestingly, the mechanistic gears are only found in the insect’s juvenile – or ‘nymph’ – stages, and are lost in the final transition to adulthood. These transitions, called ‘molts’, are when animals cast off rigid skin at key points in their development in order to grow.

It’s not yet known why the Issus loses its hind-leg gears on reaching adulthood. ̽��ֱ��scientists point out that a problem with any gear system is that if one tooth on the gear breaks, the effectiveness of the whole mechanism is damaged. While gear-teeth breakage in nymphs could be repaired in the next molt, any damage in adulthood remains permanent.

It may also be down to the larger size of adults and consequently their ‘trochantera’ – the insect equivalent of the femur or thigh bones. ̽��ֱ��bigger adult trochantera might allow them to create enough friction to power the enormous leaps from leaf to leaf without the need for intermeshing gear teeth to drive it, say the scientists.

Each gear strip in the juvenile Issus was around 400 micrometres long and had between 10 to 12 teeth, with both sides of the gear in each leg containing the same number – giving a gearing ratio of 1:1.

Unlike man-made gears, each gear tooth is asymmetrical and curved towards the point where the cogs interlock – as man-made gears need a symmetric shape to work in both rotational directions, whereas the Issus gears are only powering one way to launch the animal forward.

While there are examples of apparently ornamental cogs in the animal kingdom - such as on the shell of the cog wheel turtle or the back of the wheel bug - gears with a functional role either remain elusive or have been rendered defunct by evolution.

̽��ֱ��Issus is the first example of a natural cog mechanism with an observable function, say the scientists.

Inset image: an Issus nymph

For more information, please contact fred.lewsey@admin.cam.ac.uk

Previously believed to be only man-made, a natural example of a functioning gear mechanism has been discovered in a common insect - showing that evolution developed interlocking cogs long before we did.

In Issus, the skeleton is used to solve a complex problem that the brain and nervous system can’t

Malcolm Burrows

Mechanical gears in jumping insects

Burrows/Sutton

Cog wheels connecting the hind legs of the plant hopper, Issus

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Mystery of how fleas jump resolved

ns480 — Mon, 21 Mar 2011 10:27:57 +0000

In 1967, a scientist by the name of Henry Bennet-Clark discovered that fleas store the energy needed to catapult themselves into the air in a pad made of the unique 'elastic' protein resilin. However, in the intervening years, debate raged about exactly how fleas harness this explosive energy. Scientists came up with competing hypotheses, but it wasn't until recently that the technology necessary to record and analyse the data became available.

Using high-speed recording equipment and sophisticated mathematical models, Professor Malcolm Burrows and Dr Gregory Sutton from the ̽��ֱ��'s Department of Zoology, were able to prove that fleas use their toes to push off and propel themselves into the air, resolving the 44 year old mystery. Their findings are published today, 10 February, in the Journal of Experimental Biology.

"We were concerned about how difficult it would be to make the movies because we are used to filming locusts, which are much bigger than fleas," admits Sutton.

But he and Burrows realised that the fleas stayed perfectly still in the dark and only jumped when the lights went on. Focusing the camera on the stationary insects in low light, the duo successfully filmed 51 jumps from 10 animals. This was when they got their first clue as to how the insects jump.

In the majority of the jumps, two parts of the flea's complicated leg - the tarsus (toe) and trochanter (knee) - were in contact with the ground for the push off, but in 10% of the jumps, only the tarsus (toe) touched the ground. If 10% of the jumps didn't use the trochanter (knee), was it really necessary, or were the fleas using two mechanisms to get airborne?

Analysing the movies, the scientists could see that the insects continued accelerating during take-off, even when the trochanter (knee) was no longer pushing down. And the insects that jumped without using the trochanter (knee) accelerated in exactly the same way as the insects that jumped using the trochanter (knee) and tarsus (toe). Also, when Burrows and Sutton looked at the flea's leg with scanning electron microscopy, the tibia (shin) and tarsus (toe) were equipped with gripping claws, but the trochanter (knee) was completely smooth, preventing it from getting a good grip to push off.

Sutton and Burrows suspected that the insects push down through the tibia (shin) onto the tarsus (toe). Using a mathematical model that could reproduce the flea's trajectory, the scientists were able to confirm that the insects transmit the force from the spring in the thorax through leg segments acting as levers to push down on the tarsus (toe), solving the 44 year old mystery.

New research from the ̽��ֱ�� of Cambridge sheds light on how fleas jump, reaching speeds as fast as 1.9 meters per second.

We were concerned about how difficult it would be to make the movies because we are used to filming locusts, which are much bigger than fleas

Dr Gregory Sutton

Mystery of how fleas jump resolved

Flea jumping

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