An Illuminated Hunt
In the vast grasslands of Emas National Park, a UNESCO World Heritage site, millions of earthen towers dot the area. These are the nests of the termite Cornitermes cumulans, which can reach over two meters in height. For a few weeks each year, typically at the start of the rainy season in September and October, these mounds transform into a rare spectacle. After sunset, they begin to glow with thousands of eerie green lights, resembling a bright city.
The light is not from the termites. It is produced by the larvae of a click beetle, Pyrearinus termitilluminans. Adult beetles lay their eggs in the sides of the termite mounds. When the larvae hatch, they burrow into the mound's hard outer shell, creating a network of tunnels. Each larva then emits a steady green glow from its prothorax, the segment just behind its head. The number of glowing larvae can be substantial; after the first rains, a single mound may host nearly 180 individual points of light. This phenomenon is a carefully timed predatory strategy, synchronized with the annual mating flights of the termites and other insects.
A Fatal Attraction
The bioluminescence of the P. termitilluminans larvae is a hunting mechanism. The start of the rainy season triggers the mass emergence of winged termites (alates) and other flying insects. Many of these insects are positively phototactic, meaning they are naturally drawn to light. The beetle larvae exploit this instinct, switching on their green glow to lure prey toward the mounds.
An unsuspecting termite, drawn to the light, is quickly seized by the carnivorous larva's powerful mandibles and pulled into its tunnel to be consumed. The larvae are highly sensitive and will glow brighter when they detect the vibrations of an approaching insect, increasing the lure's effectiveness. This interaction is a direct example of a predator-prey relationship. The larvae depend on the termites for the structure they inhabit and as a primary food source during a brief period of abundance. The chemical reaction producing the light is an efficient adaptation, allowing these stationary predators to hunt mobile prey in the darkness of the cerrado savanna.