It’s no big mystery why turtles and other reptiles bask in the sun – being cold-blooded animals, they’re gathering heat to warm their bodies, so they can be active. Recently, however, scientists from Israel and the UK discovered that the Oriental hornet has been putting a “high-tech” spin on that model... the outer layers of its body work as a natural photovoltaic cell, converting sunlight to electricity. The scientists then proceeded to create a cell of their own, using the hornet as their inspiration.

The study was led by Dr. Marian Plotkin of Tel-Aviv University. It had been observed that the hornets’ underground nest-digging activity increased with the intensity of the sunlight, whereas most wasps tend to be more active in the early morning. This caused the late Prof. Jacob S. Ishay to suspect that the insects were utilizing solar radiation.

Plotkin’s team discovered that the secret lies in the hornets’ outer body shell, or exoskeleton. They found that the cuticle material making up the brown portions of the shell consists of an array of grooves, each one 160 nanometers high. The yellow parts of the body, however, are made up of cuticle material bearing a series of interlocking 50nm-tall oval-shaped protrusions, each one housing a pinhole-sized depression.

The antireflective brown material splits any sunlight that hits it into several diverging beams. These beams proceed into the cuticle, where they encounter a several-layer-thick sheet-like structure. Within each layer are rod-like structures embedded in a protein matrix, the rods made from chains of the polymer chitin. It is this complex structure that keeps the solar light beams trapped within the cuticle, bouncing between layers – the team noted that some man-made solar cells use a similar technique, in which light is bounced back and forth between layers of nanorods.

So, why the yellow? The yellow cuticle takes its coloration from the pigment xanthopterin, and it turns out that xanthopterin has the ability to change light into electrical energy. In other words, the brown areas trap the light, while the yellow areas allow it to be turned into energy.

To prove their theory, the team made a dye-sensitized solar cell, which used xanthopterin as a light-harvesting molecule. While it only had a conversion efficiency of 0.335 percent, it still did work, and could pave the way for further advances in the field.

The research was recently published in the journal Naturwissenschaften.