Have you ever settled into a favorite overstuffed armchair only to notice your coffee sitting just out of reach? In such circumstances, I often wish I could use “the Force,” the mythical energy field Jedi use to deflect blaster bolts and retrieve lost lightsabers. In the real world, humans can’t use telekinesis to manipulate objects. But some animals do employ natural electric fields to attract and repel things.
The lowercase f “force” wielded by the animal kingdom occurs when friction between two objects causes one object to lose electrons and the other to gain electrons, creating an electrostatic charge. Electrons are negatively charged, so the object that loses electrons accumulates a positive charge, while the one that gains electrons accumulates a negative charge. The electrostatic force causes charged objects to repel things with the same charge and attract things with the opposite charge. Rubbing a balloon on your head makes your hair stand up because friction causes the balloon to gain a negative charge and the hair to gain a positive charge.
Like the Force in the Star Wars universe, animals use electrostatic force for good and evil. On the “light side,” honeybees, bumblebees, and hummingbirds build up electrostatic charge as their wings move through the air. These pollinators use electrostatic force to transfer pollen to and from flowers, supporting plant reproduction and biodiversity. On the “dark side” (at least from the prey’s point of view!), predators like orb spiders use electrostatic force to trap prey in their webs, while parasites like ticks and mites use it to attach to hosts.
Scientists suspect that other winged animals could employ “light side” electrostatic force to aid in pollination, but they don’t know how widespread this phenomenon is in nature. Two biologists from the University of Bristol explored whether butterflies and moths from the order Lepidoptera performed electrostatic pollination. Scientists know that moths are widespread pollinators, but they disagree on whether or not butterflies pollinate plants.
The researchers collected wild butterflies and moths from around the UK and Germany or purchased captive-bred versions from World Wide Butterflies. They kept them in mesh enclosures with controlled climates mimicking their natural habitats and fed them from artificial flowers filled with a sugar solution or pineapple slices.
The researchers hypothesized that Lepidoptera would carry less electrostatic charge than other pollinating insects because they have smaller relative wing sizes and slower wingbeats. To test this, they measured the free-flying electrostatic charge of 72 adult peacock butterflies. They transferred each butterfly to an acrylic box lined with leaves native to their habitat to ensure the charge they carried was as close to natural as possible.
Then, they attached a ring-shaped electrode to an instrument that detects very low electric current, called a picoammeter. They placed the ring electrode next to an exit hole in the box and used the picoammeter to record each butterfly’s charge as it flew out the hole and through the electrode. They found that peacock butterflies carried an average charge of about +50 picocoulombs, actually more than other pollinating insects.
Next, the team tested whether the insects’ habitat and ecology affected their electrostatic charge. They used a similar technique to measure the charge of 4 additional species of butterflies and 6 species of moths, spanning 5 continents and a range of climates and feeding behaviors. They found that all 197 individuals they tested carried a charge sufficient to move pollen grains from several millimeters away. However, the strength and polarity (whether it was positive or negative) depended on the insects’ habitat and ecological niche. For example, tropical species were more likely to carry a negative charge than temperate species, and nighttime feeders were more likely to carry a negative charge than daytime feeders.
The researchers concluded that butterflies are actually good at pollinating. They speculated that a high charge could improve the insects’ “light side” abilities to attract pollen and sense electric fields around nectar-bearing flowers. However, carrying a high charge would also have drawbacks, since highly-charged insects are more vulnerable to “dark side” predators and parasites. They suggested that tropical and nocturnal Lepidoptera could carry a negative charge to sense predators, which are more active in warm climates and at night. May the electrostatic force be with them!
