Most people try, or at least hope, to avoid ticks. The tiny arachnids spread a variety of harmful diseases as they expand their range into new areas. But recently, two scientists embarked on a counterintuitive mission to collect as many bloodsucking ticks as possible.
“We’ve had quite a few fun afternoons of frolicking through forests of sheets,” said Sam England, a biologist at the Natural History Museum in Berlin. “Just drag them, pick up the ticks.”
He and Katie L. Lihou, then friends and PhD students at the University of Bristol in England, sought to combine their research topics into one collaborative project. Dr. Lihou is a veterinary parasitologist who studies ticks, and Dr. England is an ecologist who studies electricity and electroreception.
The resulting paper, published Friday in the journal Current Biology, provides another reason to worry about ticks. The scientists show that the static electric fields naturally produced by animals (including humans) can physically attract the ungainly creatures toward their hosts. By extending their range electrically, ticks can grab onto hosts more easily. While the finding may contribute to ticks’ fearsome properties, this knowledge could also be used to improve ticks’ antistatic defenses.
Many tick researchers have had to chase down an errant arachnid after it was swayed by static from plastic or nylon equipment due to static electricity, said Sukanya Narasimhan, a biologist at Yale University who was not involved in the new study. But popping ticks were considered nothing more than a nuisance; “We never gave it much thought,” said Dr. Narasimhan.
To better understand what happened, Dr. England and Dr. Lihou their ticks in a tightly controlled environment that attempted to mimic the conditions they face when seeking a blood meal.
When a tick tries to feed, it’s on top of a plant that’s grounded, meaning its electrical charge dissipates into the soil. To simulate this condition, the ticks were placed on a grounding plate. The researchers then passed an electrode, which charged to 750 volts, three millimeters across the mark. This voltage is comparable to or even lower than that of a typical mammal’s electric field. The ticks were invariably pulled up onto the electrode against gravity. Holding the parasites close to a similarly charged rabbit’s foot created the same flying tick phenomenon.
To get a sense of what this animal attraction might mean for a potential tick host in nature, Dr. England a computer model of the electric field around a cow.
“The geometry of a cow is very complicated,” said Dr. England, so he used a technique that breaks the dimensions down into smaller elements, making it easier to develop a model for the whole cow’s electric field.
This model revealed that the static charge from a passing bovine can exert a significant attraction on a tick searching for food on top of a blade of grass a few millimeters away. And another experiment testing the minimum force needed to attract ticks found that a surface charge of 30 kilovolts — which is extreme but theoretically possible in humans — can suck up ticks from up to a few inches away.
The ticks can be attracted to electric fields because they accumulate static charge themselves as they crawl and crawl through the world. If so, you would expect them to be attracted to fields of opposite charge, but repelled by fields of the same charge. But dr. England and Dr. Lihou discovered that ticks are attracted to both positive and negative electric fields. This finding suggests that the ticks are polarized in some way, meaning that positive and negative charges are separated in their bodies, but exactly how that polarization works is still unclear.
Dr. Narasimhan said the results were “super interesting,” but she cautioned that we can’t say for sure whether static electricity plays a role in tick life cycles until it’s confirmed with living hosts outside the lab. Dr. England agreed, suggesting that a future experiment where some sheep go through a “car wash with anti-static spray” while others don’t would be “quite a funny idea,” he said.
But he also added that he “would be very surprised if it didn’t happen in nature.” Whether in the field or in the lab, he said, “the physics don’t change.”
