Scientists found that the dark markings on a species of fluffy wasp reflected less than 1 percent of light.
The first thing to understand about velvet ants is that they are not, in fact, ants. They're wasps, some of which are wingless, and are named in part for their fluffy exteriors.
About the size of a board game die, one species of velvet ant is known for its distinct black and white markings, which dazzle the eye as the creatures scurry across tropical savanna and a dry shrub desert in Brazil called the Caatinga.
It "looks like magic," said Vinicius Lopez, an entomologist at the Federal University of Triângulo Mineiro in Brazil who studies insect coloration. The effect makes them easy to lose sight of, he said with the help of a colleague who translated his remarks to English. It is perhaps why some Brazilians refer to them colloquially as sorcerer ants.
A team of scientists led by Dr. Lopez recently found that the black parts on female velvet ants were actually ultrablack -- so matte that they absorbed nearly all visible light. The discovery, published in the Beilstein Journal of Nanotechnology this month, makes this particular species of velvet ant, Traumatomutilla bifurca, the first known insect among Hymenoptera -- the group of animals consisting of bees, wasps and ants -- to display such a striking shade.
"We have never seen this kind of color in the dragonflies or bees or beetles we have analyzed," said Rhainer Guillermo-Ferreira, another entomologist at the Federal University of Triângulo Mineiro and an author of the paper.
In nature, some blacks are blacker than others. There's your run-of-the-mill black, which is caused by the presence of melanin and displays some sheen, like the feathers on a crow. Then there's ultrablack, sometimes called superblack, a shade achieved by microstructures that swallow nearly all of the light hitting a surface.
Ultrablack pigmentation is rare in the animal kingdom. In organisms that have it, it helps them hide from predators, regulate body temperature or even attract mates, as the contrast against brighter colors can be visually enticing.
Dr. Lopez's team was trying to uncover different mechanisms for color production in insects when it realized the velvet ant was unique. A closer inspection of its exoskeleton revealed that under a dense layer of hair the insects had an intricate arrangement of thin, stacked platelets that resembled the pages of a book. According to Dr. Guillermo-Ferreira, this particular structure hasn't been seen in other animals with very dark coloring.
The researchers think the configuration of hair and platelets is key to producing the matte, ultrablack color. Because the insect's exoskeleton has so many different features, light has a higher chance of being absorbed than it would on a smoother black surface.
It's as if the light gets trapped inside all of the layers, Dr. Guillermo-Ferreira said.
Dakota McCoy, an evolutionary biologist at the University of Chicago, said the discovery was "fantastic" and commended the researchers' commitment to studying the exoskeleton of the velvet ant at different scales.
"They didn't just stop at the surface," she said. "They looked both on top and inside to try to see what the whole story was."
Compared with other ultrablack animals, female velvet ants are darker than the common birdwing butterfly, the only other insect known to display such a shade. The velvet ants' coloring is closer to that of birds of paradise and peacock spiders.
In addition to visible light, the ultrablack markings on female velvet ants also absorb nearly all ultraviolet light. That could also be a helpful defense mechanism against predators that can see wavelengths not visible to humans, the scientists said.
But it's not clear that velvet ants actually need the ultrablack pigment for camouflage. Prior work has shown that predators tend to avoid velvet ants because of their hard exoskeletons, their painful stings and the screeches they let out when in danger.
It's also a mystery why only the females of this species of velvet ant are ultrablack. The males have similar black markings, but theirs reflect much more light.
In the future, the researchers plan to investigate the environmental pressures that caused female velvet ants to evolve this way.
"In nature, you see a lot of different patterns of coloration, and we don't really know why," Dr. Guillermo-Ferreira said. But "every time we study velvet ants, they give us some new, interesting result."