Malcolm Burrows was eating his lunch in Cape Town, South Africa, when he heard a noise. Thwack! He was sitting next to a small pond surrounding by low-hanging shrubs. Thwack! And the noise kept repeating. Thwack! Thwack! Thwack!
It was coming from the water’s surface. Looking closer, he could see the reflective surface was pocked by tiny black spots, each jumping quickly from one place to another. They were pygmy mole crickets, insects that are commonly found in warm regions of Florida, South Africa, and Australia.
Using small fishing nets, Burrows and his colleagues caught a few of the insects, took them back into the lab at the nearby Zoology Building and started photographing them with a high-speed camera. Taking a snapshot every 2000th of a second, these instruments were able to capture the finer details of the crickets’ acrobatic abilities.
So how were they able to jump from the surface of water, and why is their ability to do so particularly remarkable?
We’ll tackle the second question first. As seen in the BBC documentary Life, a few large animals like grebes and Basilisk lizards (aka ‘Jesus lizards’) can actually run across the water’s surface for short distances.
Their burrows can get flooded if they’re not careful
But the real masters of water walking are smaller animals like insects. Water striders and mosquitoes, for instance, can easily float, glide, and walk on water for extended periods.
Insects don’t generally jump from water, though. Because of the weak attractions between molecules of water, the surface layer is like sticky elastic to these small animals. Insects struggle to break free from these liquid clutches.
Not pygmy mole crickets, however.
Confusingly, these insects aren’t actually crickets. “It’s a bit of a misnomer,” says Burrows. “They’re much more closely related to grasshoppers.” But they certainly are pygmy, measuring only half a centimetre long.
Like their grasshopper kin on land, these insects have huge hind legs for jumping
Since they live in burrows near ponds and streams, there has been a strong evolutionary pressure for this species to be able to get out of the water. “They live a precarious life,” says Burrows. “Their burrows can get flooded if they’re not careful.”
But their biggest danger is their neighbours. “They live next door to larvae of tiger beetles, which are voracious predators,” says Burrows. Without functional wings, they can’t fly away. But boy can they jump! Avoiding the hungry mouths of these predators often ends in a splash landing.
So how do they break free from the sticky clutches of the water’s surface?
Like their grasshopper kin on land, these insects have huge hind legs for jumping. For pygmy mole crickets, they are so big that they can’t use them for everyday walking. Folded at the ‘knee’ joint, they remain elevated above the ground waiting to be deployed for their one purpose – jumping. This means that pygmy mole crickets actually use only four of their six legs when it comes to walking.
It doesn’t sound like much, but it’s like a human jumping over 100ft (30.5m) from a standing start
These hind legs aren’t like those of other grasshoppers, however. They are adapted to a life aquatic. As revealed by his high-speed cameras, Burrows showed that when their long legs hit the surface of the water a series of flattened paddles flare outwards.
“And they hugely increase the surface area of the leg,” says Burrows. Like the oars of a boat, this larger surface can then push a greater amount of water and add more oomph to the insect’s jump.
After being propelled out of the water at over two metres per second, their paddles are pulled back towards the legs by elastic hinges, streamlining the cricket’s takeoff. Once airborne they spin backwards and can reach heights of over 10cms. It doesn’t sound like much, but that’s like a human jumping over 100ft (30.5m) from a standing start. And from a surface that is inherently trying to pull them down.
How does such a tiny animal produce so much power?
It’s all to do with the slow movement of its muscles. Just like an archer slowly pulls a bowstring, pygmy mole crickets gradually contract their leg muscles and store the resultant energy in a region of their knee joint that is both elastic and tough.
As they leave the water, pygmy mole crickets experience G-forces of over 160
“Just like an archery bow that’s made out of hardwood and softwood together, those two properties when combined mean that the bow is much stronger and doesn’t break,” says Burrows.
Then the pygmy mole crickets let go of this stored energy. “[They’re] releasing it suddenly, so all the power is being delivered very rapidly.” The same catapult mechanism is at work in the tongue of chameleons, allowing an otherwise small mass of muscle to produce a tremendous amount of power.
As they leave the water, pygmy mole crickets experience G-forces of over 160. “[We] would pass out at about five,” says Burrows. Their small size, tough exoskeleton, and lack of a circulation system like our own, protects them from any ill effects during lift off. “The performance of these insects is quite staggering.”