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A surgeon wielding a micro-scalpel cuts through the head capsule of her subject, the nocturnal sweat bee Megalopta genalis, in a lab at the Smithsonian Tropical Research Institute in Panama. The surgeon, a researcher working under Dr. Eric Warrant, of Lund University in Sweden, inserts a glass electrode thinner than a micrometer into the bee’s brain. She is trying to pierce something very small—a monopolar cell in a layer at the top of the brain called the lamina. Warrant believes these cells are responsible for a trick called neural summation, which helps the bees maximize the use of light photons to see in their dark habitat—the dense tangled undergrowth of the nighttime Panamanian rainforest. “It seems that these bees are able to do something that almost defies physics,” says Warrant, a functional zoologist who has been researching nocturnal vision in insects for more than two decades. “We believe the miracle of how the bees see so well at night is happening here in these lamina monopolar cells.”
M. genalis nest inside small sticks and forage for pollen in the hour right after sunset and the hour and a half before sunrise. Dr. William Wcislo, acting director of the Smithsonian Tropical Research Institute, theorizes that the bees feed during these dim hours because there is less competition for pollen and fewer predators. Humans would hardly see anything in the dark rainforest, but sweat bees forage with no problem, avoiding dangling lianas and drooping palms and returning home to a nest the width of a magic marker, with an opening just barely larger than their bodies.
The bee brain surgery requires such precision that even the researcher’s own foot tapping could jostle the table enough to misalign the tiny electrode.
Vision relies on the ability to process photons. Humans have what are known as camera lens eyes, which collect photons and direct them to the photoreceptors in the retina through a single lens. That works well in daylight with plenty of photons. But on a clear moonless night, any single spot on earth receives 100 million times fewer photons than it does on a clear sunny day. Nocturnal creatures evolved to maximize the photons’ use. If we understand how sweat bees do it, we may be able to build our nighttime navigation equipment to do the same.
That’s what the Unites States Air Force is after. “The nocturnal bees that Eric and his people look at in Panama do some light collection and processing tricks that allow them to see in conditions when most insects cannot see, and we are interested in that kind of trick,” says Ric Wehling, a senior research engineer at Eglin Air Force Base in Florida. The agency is pondering a future breed of Micro Aerial Vehicles (MAVs) that wouldn’t have to rely on GPS. These MAVs would be able to visually comprehend the world and see in the dark just like the bees.
Bees have more eyes than humans. They also have eyes of different types that perform different functions. The ocelli are the three camera-type eyes similar to our own; they form a triangle on the insects’ head. They produce blurry images but help insects orient themselves by detecting the up and down by way of light (up is the sky, which is typically lighter, down is the ground which is typically darker). Bees also have a pair of compound eyes, which is composed of thousands of tiny towers called ommatidia, which are packed tightly together, forming the honeycombed eye surfaces on bees’ heads. At the top of each ommatidium tower is a lens that captures photons and directs them down to the photoreceptor cells inside the ommatidium. Diurnal insects like honeybees have what are called apposition compound eyes, which means that each photoreceptor inside each ommatidium receives photons from only one ommatidium. This works for diurnal insects because enough photons come through a single ommatidium for the photoreceptors to generate a clear image. Most nocturnal insects have superposition compound eyes in which each photoreceptor receives photons from hundreds of ommatidia. This eye design assures that a far greater number of photons reach each photoreceptor, producing a brighter image, which allows nocturnal insects to see well in the dark.
But the mystery of M. genalis is that they don’t have the superposition compound eyes capable of netting in a greater number of photons. The sweat bees have the apposition eyes that are best-suited for daytime use. Instead, the sweat bees have larger ommatidia and ocelli than nocturnal insects with superposition compound eyes. The bees’ photoreceptors are also more sensitive than those of diurnal insects, meaning they produce a stronger neural impulse when hit by a photon. But this comes at a price. Having stronger neural impulses is like turning the volume on a radio with a bad reception—the music is louder, but so is the static, or as optical entomologists call it, the noise. To weed out the noise, bees’ monopolar cells sum up signals from numerous photoreceptors.
M. genalis is not the only creature capable of the neural summation trick. Warrant says several other nocturnal bee, wasp, and ant species may be doing it too. Animal and human brains perform their own types of neural summation to improve the quality of input. “Summation is a way of making the best out of a bad situation,” Warrant says. “Brains are very good at making efficient calculations with limited numbers of input.” He believes that human brains might be using similar summation methods when processing sounds or smells. But this kind of photon-generated impulse summation is beyond our brain’s reach, and that’s why Warrant’s researcher is inserting electrodes into the monopolar cells of M. genalis.
The bee brain surgery is done on a vibration-canceling tabletop because it requires such precision that even the researcher’s own foot tapping could jostle the table enough to misalign the tiny electrode she is placing into the monopolar cell, which is about the width of a human hair. To keep still, the bee is placed inside a small vial that leaves exposed only its head. The operation is done inside a metal mesh cage that keeps out extraneous electrical noise that can interfere with detecting the electrical signals in the brain. “An electrode can act a bit like an antenna,” says Warrant, “and pick up this noise and that would contaminate the signal you are trying to record from the neuron.” Using a syringe, the researcher fills the electrode with a conductive solution that will carry the electrical impulses from the monopolar cells through a wire into an amplifier and to a computer to be analyzed.
The experiment is done in a darkened room to mimic the bees’ habitat. A black pixel on a white screen is moved in front of the bee. If the electroded monopolar cell gives off a neural response only when the pixel is in front of the ommatidium directly above the cell, the neural summation is not happening (it means that each monopolar cell receives input from only one ommatidium). But if the electroded monopolar cell produces neural responses across the wide arc of the bee’s visual field as the pixel is dragged across, it means the cell receives input from multiple ommatidia and the neural summation is happening.
Warrant hopes to have enough data to prove his neural summation hypothesis by June 2014. If it confirms, building nighttime vision for machines and humans could be possible. We won’t be able to teach our brain cells to summate the scarce nighttime photons, but night sight may be as easy as donning bee goggles.
Justin Nobel’s stories about science and culture have appeared in Time, Orion, and Tin House. Among other projects, he is currently working on a book of tales about the weather. He lives in New Orleans.
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