Red-headed centipede touches the sun

Under the leaves of East Asian and Australian forests, pencil-long red-headed centipedes sneak in the dark. This venomous arthropod can’t tell the difference between light and dark — because they don’t have eyes.

A red-headed centipede uses its antennae to detect the temperature of sunlight as it crawls along a log. Image source: Yang Shilong

Now, researchers already know how the centipede avoids damage from sunlight when it is out of sight. When sunlight hits their antennae, it triggers a heat-related reaction that reminds them to seek refuge in the dark. The study was published in the Proceedings of the National Academy of Sciences on February 13.

Paul Marek, an entomologist at Virginia Tech and State University who was not involved in the study, said their antennae are covered with muscles and covered with sensitive hair-like protrusions that help them perceive their surroundings. It’s like a blind person fumbling in the dark with a cane.

Polypods, such as centipedes and millipedes, have gradually deteriorated their eyesight over the course of evolution, while some of them have lost their eyes altogether. In the dark world under the deciduous layer, vision is less important than touch. They use their sense of touch to determine prey, including worms, spiders, scorpions, and even small reptiles and mice.

Lack of vision does not make this animal any less dangerous. The venom released by the red-headed centipede can wreak havoc on the circulatory system of prey; Its chela can also pierce human skin, causing burning pain, and even requiring medical treatment in severe cases. In the lab, researchers observed red-headed centipedes killing mice 15 times their size in just 30 seconds.

Red-headed centipedes not only lack vision, but also lack light-sensitive proteins. So, how does it know if it has been accidentally exposed to sunlight and how to avoid predation by snakes and birds?

To find out, researchers such as Yang Shilong, a molecular biologist at Northeast Forestry University in China, placed the centipede in two adjacent transparent containers, one of which was completely covered with black tape. The researchers placed a lamp above the device to simulate sunlight and recorded their activity in both bright and dark environments. They also mounted a thermal imaging camera on the centipedes to determine how they reacted to temperature.

Whenever centipedes crawl toward a dark container, infrared images show a lot of heat concentrated on their curled tentacles. Within 10 seconds of exposure to light, the temperature of their antennae rose from about 28°C to more than 37°C.

The researchers then dissolved some of the sensory nerves in their antennae to determine their chemical composition, and found a heat receptor called BRTNaC1, an ion channel that transports charged atoms between cells through the antennae. BRTNaC1 is triggered at 33°C to 48°C. The researchers say that when light heats the centipede’s tentacles, it activates BRTNaC1, triggering a physiological response that alerts the centipede that it has entered dangerous sunlight.

To confirm this light-sensing effect, the researchers covered the centipede’s antennae with tin foil to block its exposure to light. These centipedes leave the dark environment much more frequently than those with bare antennae.

Both Yang and Marek believe that red-headed centipedes are not the only soil organisms that use heat receptors to detect light indirectly. Marek says they just don’t have eyes, but there are other parts. “Nature has come up with interesting workarounds that allow them to detect light without eyes.” (Source: China Science News, Wang Jianzhuo)

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