Mantis shrimp larvae are completely invisible underwater, according to a new study that explains the science behind this natural conjuring trick.
The eyes are key to becoming invisible, according to the study, published in The Journal of Experimental Biology. The goal is to see but not be seen.
"For small animals in the pelagic environment, such as marine crustacean larvae, survival in such a featureless world often depends on the ability to avoid being seen," authors Kathryn Feller from the University of Maryland Baltimore County and colleague Thomas Cronin wrote.
Photos: Animal Superpower–The Eyes Have It
Eyes are the one part of the anatomy that most creatures cannot make transparent, so the researchers wondered if the shrimp larvae's eyes were visible under water, or if something else was happening to make the eyes invisible to others.
The light bulb moment for the scientists really was a light bulb moment!
Feller explained that she traveled to Lizard Island Research Station on Australia's Great Barrier Reef, where she could wade into the tropical waters at night to lure tiny mantis shrimp larvae into her net.
Next, she illuminated the larvae's eyes with white light back in the lab. She now recalls that the display was dazzling.
"The whole sphere of the retina at the center of the eye reflects this sparkly blue-green light; it's quite brilliant," Feller remarked in a press release.
Photos: Innovations Inspired by Animals
The scientists measured the spectrum of the reflected light, known as "eyeshine." They also noticed that the minute mirrors in the eyes of Pseudosquillana richeri and Harpiosquilla larvae (the shrimp to be) only reflected blue-green light.
"They produced very discrete peaks in that region of the spectrum," Feller said.
When she investigated the eyes of Pullosquilla thomassini (yet another type of mantis shrimp), however, she was amazed to see that the upper region of the eye produced green reflections, while eyeshine from the lower portion of the eye was blue.
"We suspect that it is something similar to counter shading; perhaps the dorsal part of the eye is held against background that is greenish and the ventral part of the eye is more bluish," she said.
Video: Can We Make Plastic from Shrimp?
To determine how well these reflections conceal the larvae's otherwise conspicuous eyes, Feller donned SCUBA gear and took some of the larvae back to the ocean so that she could photograph their eyes against the natural background.
"It was very labor intensive to get the in situ images," she recalled, adding that it took an entire day to collect shots of each larva from different directions at various depths and times.
When she recreated the conditions back at the lab, sure enough, there was virtually no contrast between the eye reflections and the shrimp larvae's natural surrounding lighting environment.
Massive Mantis Shrimp Hauled in From Florida Dock "Larval eyeshine does a really nice job (of making the eyes appear invisible)," Feller said. "I didn't expect it to do as good a job as it does."
She and Cronin now suspect that larvae found in other waters produce eyeshine with a completely different spectral range that is probably tuned to their light environment too.
Photo: Invisible shrimp larvae made visible via lighting out of water. Credit: Megan Porter