Pygmy Mole Crickets Are Prodigious Jumpers

The size of a grain of rice, the 'pygmy mole cricket', which belongs to the family Tridactylidae, lives most of its life tunneling under the sand along the margins of water bodies.  These insects are known to be exceptional jumpers.

These pygmy mole crickets were observed by professor Malcolm Burrows from the University of Cambridge's Department of Zoology while having lunch near a pond in Cape Town, South Africa. He was fascinated with the sporadic noises coming from the water body and noticed insects jumping on the surface of the water. These insects were the pygmy mole cricket. He saw their jumps could reach distances of 33mm (5.4 times the length of their body) and 100mm high.

He then collected a few samples and carefully analyzed them in his lab. He cautiously noticed their jumping behavior under a high speed camera. He was accompanied by his engineer colleague, Dr Gregory Sutton.

He noticed what makes the pygmy mole cricket different from other animals that use the surface tension of water such as pond skater insects (also known as water striders) or basilisk (Jesus) lizards to traverse water is that the cricket uses its enormous and powerful hind legs to push a small ball of water down to propel itself off the surface.

In order to protect themselves from the fish they push their powerful hind legs into water.  As they push downward, specialized spring-loaded paddles and spurs fan out to increase the surface area enabling them to propel a ball of water downwards, launching them upward into the air. The moment the thrust has been applied, the paddles then rapidly snap close to reduce the drag.

Professor Burrows said: "For small insects, water can be a deadly, sticky trap; water grabs and holds an insect, offering it as an appetizing snack for an alert fish. Other animals use surface water tension, keeping a small layer of air between their feet and the water. However, if their feet get wet, they will be pulled into the water and drown. Pygmy mole crickets turn the stickiness of water to their advantage and use this property to enable jumping."

The researchers hope that this unique technique used by the pygmy mole crickets to jump on water could be used in the development of small water robots.

Professor Burrows added: "If we want to make small robotic vehicles that move under water, this is how we would have to design propellers or oars."

Pygmy mole crickets, which are also known as pygmy sand crickets or pygmy mole grasshoppers, apparently ingest sand particles and whatever algae and other organic matter adheres to them. 

The findings were reported Dec. 3, in the journal, Current Biology.

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