A Living Machine

What am I looking at?

This is the joint between the body and hind legs – the propulsive, or jumping, legs – of a Fulgoromorpha planthopper at the nymph, or larval stage. The gears (1) are located on the insect’s first mobile leg segment, called the trochanter; the legs continue to the left and right of the gear but aren’t visible in this image. As you can imagine, when the gears are brought together, the only way for the legs to move is in perfect synchrony; coupling the movement is the function of the cogs. But when it’s walking rather than jumping, the insect can uncouple its legs.

Click on the right arrow to see an even closer view of the gears.

Biology in the background

Planthoppers belong to the order Hemiptera, commonly called true bugs. They are related to other jumping bugs like leafhoppers, treehoppers, and froghoppers. Jumping is one of the fastest and most powerful movements generated by animals; it’s frequently used to escape from predators, so the cost of failure is high.

The speed and power of the planthopper’s jumping movement requires synchronization of its two propulsive legs to within 30 microseconds of each other (a microsecond is a millionth of a second!). Without this synchrony, its body would spin but there would be little forward movement. Such levels of synchronization are beyond the limits of neural control but can be accomplished mechanically by these gears. The meshing of the gears ensures that when one hind leg moves, the other one moves at the same instant.

The gears disappear as the insect grows to adulthood, when it can use its wings to stabilize its jumps, eliminating the need for coordinated leg movements. In addition, the gears’ functionality diminishes with time, due to wear. When nymphs molt, they produce a whole new exoskeleton, along with a crisp, new set of gears. But the adults lack the ability to regenerate worn-out body parts.

Some planthoppers are only about 20 millimeters long as adults, or roughly the width of a human thumbnail. But tropical lanternflies can grow as long as 115 millimeters, or roughly 5.5 times larger than a human thumbnail. In the largest planthopper known – the invasive spotted lanternfly, which lives on the East Coast of the United States – the gears in its final instar are about 1 millimeter in diameter, or roughly 13 times larger than the width of a human hair.

Technique

These images were created using confocal microscopy.