On a quiet evening in rural Brazil, a tiny train emerges from beneath the forest litter. Two red headlights light its path, and 11 pairs of yellow-green lanterns illuminate its sides. To be sure, this is no ordinary train. Rather, it is a 70-millimeter-long larva of the Phengodidae family of beetles, found in North and South America. Because females, which retain their larval form, resemble internally illuminated railway cars, they are often called railroad worms. Brazilian country folk call them little trains.
During the day the dull-brown larva is hard to spot. But at night it advertises its presence with its amazing array of lights. These are energized by the organic substance luciferin, which, aided by enzyme luciferase, oxidizes to produce cold light. Colors of the light include red, orange, yellow, and green.
The red headlights glows almost constantly –but the yellow-green lateral lights. Research suggests that the headlights help the larva to find millipedes, its favorite prey, whereas the sidelights seem to discourage predators, such as ants, frogs, and spiders. In effect, the glow says “I am unpalatable. Go away. Accordingly, the sidelamps luminescence when the larva senses a potential predator. They also shine when its attacks millipedes and when the female is curled around her eggs. Under normal circumstances, the sidelights build up to peak intensity and then darken –all within a few seconds –repeating the cycle as often as necessary.