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The Fascinating Relationship Between Hummingbird Flower Mites and Electricity

A study reveals that tiny mites riding on the beaks of hummingbirds employ an unexpected means of navigation: electricity.

These specialized mites, known as hummingbird flower mites, thrive on nectar within specific flowers associated with their species. When it’s time to relocate, they hitch rides on hummingbirds, but researchers have long been puzzled by how these minuscule arachnids manage to disembark accurately at their destination flowers. Recent findings led by Carlos Garcia-Robledo, an associate professor in the Department of Ecology and Evolutionary Biology, shed light on this question, as detailed in the journal PNAS.

Garcia-Robledo’s research encompasses the evolutionary pathways of organisms and their adaptations to climate change, including the enigmatic behavior of these mites.

“When hummingbirds move from flower to flower, the mites only descend from their beaks upon contact with the first flower,” Garcia-Robledo noted. “I found this behavior intriguing and began to question why they did not proceed to the subsequent flowers.”

For many years, the scientific community hypothesized that odor might be the guiding signal for the mites. However, after conducting experiments to evaluate this premise, Garcia-Robledo remained skeptical about the role of scent.

“Observing the mites in a lab setting showed me that they were indifferent to flower odors. It was evident to me that another factor must be at play,” he explained.

An epiphany came when he encountered research about how ticks utilize static electricity to hitch a ride on clothing, coupled with an unexpected lunch meeting whilst at the La Selva Research Station in Costa Rica.

“This recollection of the perplexing behavior of the mites led me to consider the possibility of electrostatic interactions,” he remarked. “These mites operate at a scale where even minimal electric fields could have significant implications for their behavior, potentially clarifying how they efficiently create their travel arrangements with hummingbirds.”

During this fortuitous lunch, Garcia-Robledo shared his theory with colleagues Konstantine Manser and Diego Dierick. Manser, a Ph.D. student from the University of Bristol working on tick research, and Dierick, an electronics specialist at the Organization for Tropical Studies, agreed to test the hypothesis.

“They suggested that implementing the idea would be straightforward, and the following day, we constructed the necessary devices. When we introduced the first mite to the setup and activated it, we were amazed at how quickly they responded. That’s how we verified their reliance on static electricity,” Garcia-Robledo recounted.

Buoyed by these initial results, the team delved deeper, experimenting with a setup that generated only static electricity to discern whether the mites were attracted to it or to frequency variations. Remarkably, they found that the mites did not react to static alone, but responded enthusiastically when the field was modulated.

“The mites’ responses were linked to vibrations and frequency patterns associated with hummingbirds, which oscillate between 20 and 160 Hz,” Garcia-Robledo explained.

As hummingbirds flap their wings, they generate an electrical charge that effectively supercharges their bodies. Much like the static shocks one might experience after walking across a carpet, the first flower encountered appears to generate the right electrical potential for the mites to either board or exit their tiny transport.

In another revealing experiment, Garcia-Robledo created a simple apparatus to test the mites’ reaction to slight positive electrical charges. Using a glass tube and a wire connected to either aluminum or copper to generate a charge, the team observed the mites reacting actively toward the positive pole at varying electrical fields, but specifically when the frequency of the signal was 120 Hz.

“By applying a charge to this small setup, the mites instinctively move toward the positive pole, even in the presence of negligible charges. The quick oscillation of the signal is sufficient for them to determine their direction,” shared Garcia-Robledo.

Each of the 19 species of mites at La Selva shows preferences for particular flowers, demonstrating an innate ability to recognize the correct moment to hop on or off their avian transport.

“We theorize that there could be specific electric signals or distinct charges designated for different flowers,” noted Garcia-Robledo. “We also discovered that certain structures in their front legs seem adept at sensing these electric charges and frequencies. The next phase of our research will explore how various mite species may possess different leg structures that could allow them to detect a range of frequencies.”

In addition to indicating when to disembark, electric charges also facilitate the mites’ rapid boarding of their feathered companions. Similar to the findings regarding ticks, the mites are drawn from flowers to the hummingbird’s beak by the positive electrical potential of the bird.

“When exposed to the electric field, we discovered that these mites are among the quickest terrestrial creatures for brief moments,” Garcia-Robledo stated. “This revelation was astonishing; the mites were not merely responding to electrostatic forces but were actually engaging with a signal produced by a living organism. This could represent a groundbreaking instance of organisms using electrical cues for both transportation awareness and the act of boarding itself.”

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