Anyone who walks through the tall grass during a walk can get unwanted company from a tick. And for that you don’t even have to actually touch the blade of grass on which the tick is sitting, write British researchers in Current Biology. Because although ticks cannot jump, they appear to be able to make good use of static electricity. As a result, they can bridge distances of a few millimeters in the air, more than their own body length.
There are almost a thousand species of ticks known worldwide. About fifteen of these occur in the Netherlands. By no means all those ticks target human blood. The common sheep tick (Ixodes ricinus) is one of the species that have humans as ‘hosts’, among others, and can also transmit the Borrelia bacteria. That bacteria can cause Lyme disease.
Rubber soles
Everyone who has ever received a static shock knows that people can be electrically charged. That charge is created by friction (for example from a balloon over a fleece sweater or from rubber soles over carpet) and is released in the form of a shock when you subsequently touch a conductive material – think of a door handle. Other mammals also have such an electrostatic charge, just like birds and reptiles: all animals that sometimes serve as a host (ie food source) for a bloodthirsty tick.
Such an electric field can have an attractive effect. If you hold the rubbed balloon near your hair, it will stand upright. Could it not be possible, the British biologists wondered, that static electricity in the vicinity of vegetation also has an effect on ticks?
To investigate this, they held ticks with stainless steel tongs near statically charged rabbit legs, and discovered that the ticks were actually attracted to the legs: they could bridge distances of a few millimeters to even centimeters through the air. No small feat, as the ticks themselves averaged 1 millimeter in length.
They then used computer models to calculate the ‘electrostatic footprint’ of various sign hosts. For example, a cow appears to be most strongly charged near the nose, tail and legs, and the surface tension of a static cow can certainly be around 750 volts. Certainly at a few millimeters distance from the grass, the strength of the electric field is such that the tick can be attracted.
Vertical movement
In follow-up experiments, ticks were placed on an aluminum plate under an electrode. When that electrode was on, with a voltage of 750 to simulate the cow, the ticks were attracted to it. Some ticks bridged the entire distance of 3 millimeters, others rose a little way from the plate. When the electrode was not on, the ticks did not come off the plate, with the exception of one tick that moved slightly upwards. But that movement arose, the researchers say, because the tick was just moving on its own.
The smaller the distance to be bridged, the lower the voltage required: for 0.1 millimeters, for example, 26 to 29 volts is sufficient. In addition, the ticks in the experiment had to move upwards, against gravity. For a vertical movement, from a blade of grass to a human leg, a less strong electric field may suffice. Although the study only involved nymphs, or young adult ticks, the researchers suspect that the static attraction also applies to adult ticks on the basis of as yet unpublished results.
Special hiking clothes
Since ticks cannot jump, this static electricity helps them land on a host. The electric field probably also ensures that they do not immediately let go, even before they have had a decent bite. The ticks may even be able to sense the electric field of other animals, the researchers speculate. This way they know better where to look for their host. But there is no clear evidence for this theory yet.
Where the authors see potential in any case is the development of special anti-static hiking clothing. Ideally, such clothes would greatly reduce the number of tick bites, and thus the number of Lyme disease infections.
Incidentally, the ticks are not the first animals in which the effect of electric fields has been studied: even spiders that move through the air on a gossamer-thin thread on windless days, sometimes use static electricity.
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