These hummingbird flower mites feed on nectar and live within specific flowers for their species. When it is time to seek out a new flower, they hitch a ride via hummingbirds. For years, researchers have not been sure exactly how these tiny, crawling arachnids quickly disembark at the right flower.
The study, led by the University of Connecticut and in collaboration with the University of Bristol, and published in PNAS, suggests that there may be some specificity in the electric signals or different charges for flowers that provide the right signal.
Co-author Konstantine Manser, based in Bristol’s School of Biological Sciences, said: “These mites can not only take flight to attach to their hummingbird hosts but they also detect incoming hummingbirds based on the bird's electrostatic fields.
“Basically, the whole interaction is governed by a force completely invisible to humans.”
Carlos Garcia-Robledom, Associate Professor in the Department of Ecology and Evolutionary Biology at the University of Connecticut, studies aspects of the evolutionary and life histories of organisms and how they respond to climate change, including this puzzling behavior.
“When hummingbirds visit multiple flowers, you usually see the mites going down their beaks only when they touch the first flower,” he explained. “I thought that was interesting and wondered why the mites were not going to the second or third flower.”
For years, researchers have proposed that the mites use a smell signal, but a breakthrough by Bristol academics studying the effect static electricity has on ticks, triggered a change of tactics.
Mr Manser added: “It wasn't too long before we were in the lab waving plastic rods over mites trying to see if they could 'ping' from the desk surface to the rod under the influence of electrostatic attraction.
“There was no question, these mites were being influenced by the electrostatic forces from the rod.
“From there, we hypothesised that the charge on hummingbird beaks might be enough to allow these mites to ‘leap’ through the air.”
With that immediate success, the researchers were inspired to experiment further with a power source that only generated static electricity and test whether the mites were attracted to statics or the frequency that it was transmitting. They discovered that when the field was only static electricity, the mites did not respond, yet they did when the field was modulated.
“The mites respond to the bouncing of a signal that is associated with the size, geometry, and vibration of the hummingbirds, which reach frequencies between 20 and 160 Hz,” said Dr Garcia-Robledom.
As the hummingbirds beat their wings, they generate a charge, and their bodies become supercharged. The first flower seems to be where mites have the electric potential to embark or disembark quickly.
The next step is to study a wider variety of mites to see if different mites can detect different frequencies.
“This may be the first kind of case where these organisms are using, at the same time, electricity to locate organisms that they are using for transportation, but also for transportation itself,” he concluded.
Paper:
‘Electric transportation and electroreception in hummingbird flower mites’ by Carlos García-Robledo, Diego Dierick, and Konstantine Manser in PNAS.