Harnessing the Power of Tiny Creatures: The Electric Mite Revolution

These hummingbird flower mites thrive on nectar and reside within certain flowers chosen specifically for their species. When the time comes to explore new flowers, they ride along with hummingbirds, but for years, scientists have been unsure about how these tiny creatures manage to jump off at the right spots. Researchers, including Carlos Garcia-Robledo, an associate professor in the Department of Ecology and Evolutionary Biology, have been working on this puzzle and shared their findings in PNAS.

Garcia-Robledo looks into the evolutionary aspects and life histories of various organisms, as well as their responses to climate change, with a focus on this intriguing behavior.

“When hummingbirds stop by multiple flowers, the mites typically only descend from their beaks upon contact with the first flower,” notes Garcia-Robledo. “I found that fascinating and questioned why the mites were not moving to the second or third flower.”

Researchers have long theorized that scent cues might be at play, but after conducting experiments to evaluate this hypothesis, Garcia-Robledo was not convinced.

“I suspected that smell might not be a key factor, as when I brought the mites into a lab, they showed little interest in flower scents. It had to be something else,” he stated.

Then, after reading about research on how static electricity causes ticks to latch onto clothing and attending a serendipitous lunch meeting at the La Selva Research Station in Costa Rica, everything fell into place.

“The peculiar observation about the mites came to mind, and I thought that there might be some electrostatic phenomenon at work,” he explained. “These mites are so tiny that they exist in a different realm of perception, so even minor electric fields could be significant for them. This might clarify the mystery of how they can swiftly hitch a ride on these birds.”

During a lunch with colleagues and co-authors Konstantine Manser and Diego Dierick, Garcia-Robledo shared his idea of testing this theory on the hummingbird flower mites. Manser was then a Ph.D. student at the University of Bristol, involved in the tick static research, while Dierick was a scientist at the Organization for Tropical Studies and an expert in electronics involved in various projects at La Selva Research Station. Together, they decided to put Garcia-Robledo’s hypothesis to the test.

“Diego and Kosta assured me it would be straightforward, and we should pursue it. We constructed the devices the next day and took the first mite from a flower to conduct our test. Once we activated the device, the mites responded immediately. That was how we confirmed they were using static electricity,” Garcia-Robledo shared.

Following this initial success, the researchers were motivated to explore further, using a power source that generated only static electricity to see if the mites were drawn to electric fields or the frequency transmitted. They found that the mites did not react solely to static electricity; they responded when the field was modulated.

“The mites reacted to signal bouncing related to the size, shape, and vibrations of hummingbirds, which produce frequencies between 20 and 160 Hz,” Garcia-Robledo stated.

As the hummingbirds flap their wings, they create an electric charge, effectively supercharging their bodies. Similar to how one might feel a minor static shock after walking across a room and touching a metal doorknob, the first flower appears to be where the mites have the right electric potential to either jump on or off their hummingbird transportation.

In another experiment, Garcia-Robledo investigated how the mites detect very slight positive electrical charges. He employed a simple yet effective setup with a glass tube and wires, where touching the wire to either an aluminum or copper plate would create a charge. The glass tube housed the mite, and when the device was charged, the mites responded by moving towards the positive pole at both higher and lower electrical fields, but only at a frequency of 120 Hz.

“You charge the small arena, and right away, the mite is attracted only if you have that little bounce of the signal. They instinctively move towards the positive charge, even with extremely small charges. The moment you initiate the bounce, it’s enough for them to pinpoint where to go, and they take off,” Garcia-Robledo explained.

Every one of the 19 mite species observed at La Selva gravitates towards a particular group of flowers, and somehow they recognize when they’ve arrived at the correct flower, signaling it’s time to jump on or off the hummingbird.

“We believe there may be specific electric signals or varying charges linked to different flowers,” Garcia-Robledo hypothesizes. “That’s one possibility. We discovered a structure on their front legs that allows them to sense these electric charges and frequencies. The next step involves examining multiple mite species, as they possess different structures in their legs, which may allow them to detect various frequencies.”

In addition to indicating when to disembark, these electric charges also facilitate the mites in efficiently boarding their fast-moving escorts. Much like ticks that leverage static electricity to catch a ride on clothing, the mites are drawn from the flower to the hummingbird beaks by the positive charge of the bird.

“When the mites are attracted by that electric field, we found they are among the fastest terrestrial organisms for a brief moment,” Garcia-Robledo remarks. “This discovery is quite astonishing because the mites were not simply reacting to electrostatics; they are responding to an actual signal produced by a living organism. That was truly unexpected. This may represent one of the first instances of organisms using electricity simultaneously for locating their transport and for the act of transportation itself.”