Ticks

Sheep tick (Ixodes ricinus)

Also called the castor bean tick, and neither name is much help: it is not confined to sheep and it is not confined to farmland. It waits on low vegetation — bracken, long grass at the edge of a path, heather, damp woodland understorey — with its front legs held out, and takes hold of whatever brushes past. It does not jump and it does not drop from trees.

Its year has TWO peaks rather than one. The first and larger comes in spring, around the middle of May; the second and smaller in September. A dry hot spell puts it on pause — it dries out easily, and on scorching days it retreats into the leaf litter instead of questing. That is why a wet week at the end of August brings it back.

It needs moisture more than it needs warmth, which is why the west and the uplands suit it and why deer and sheep country tends to carry more of it. We do not turn that into a map — see below.

Lyme disease, and what about tick-borne encephalitis

Lyme borreliosis is the reason to take a bite seriously. Most bites do not pass it on, and the risk rises with the hours the tick stays attached, which is the whole argument for checking yourself the same evening rather than the next day.

The sign people are told to look for is a rash that spreads outward from the bite over days — often, though not always, clearing in the middle. It usually appears one to four weeks after the bite, not immediately, so a bite that looks fine on the day is not evidence of anything. Fever, aching joints and unexplained tiredness in the weeks after a bite are reasons to see a doctor and to mention the tick.

Tick-borne encephalitis is a separate illness and a much smaller story here. A small number of cases have been confirmed in Britain in recent years, in a few specific areas. It is not the widespread risk that it is across parts of continental Europe, and it is not the reason most people should be checking for ticks — Lyme is.

What our forecast says, and what it does not

It says one thing: whether ticks are out, and by which species' threshold we worked that out. It does not give a number.

That restraint is deliberate. The thresholds are measured — mean temperature over the week, and soil temperature, because a tick does not come out of frozen ground however mild the air is. An activity score we could only estimate, and next to a measured threshold an estimate would look just as solid.

We do not know where there are more ticks. There is no British risk map in this system and we are not going to invent one. The Russian section of this site shows official lists of endemic districts; that document is about Russia and means nothing here.

Two other tick species appear elsewhere on this site and not here, because they do not occur in these islands: the taiga tick (Ixodes persulcatus) and the brown dog tick (Rhipicephalus sanguineus). The forecast does not count them for Britain either.

If you find one on you

Take it off straight away and take all of it off. Transmission risk grows with the hours it stays attached, so haste here is justified.

• fine-tipped tweezers or a tick tool, gripping as close to the skin as you can — by the mouthparts, not by the body;
• steady pull straight out: no jerking, no twisting;
• no petroleum jelly, no alcohol, no burning it off — these irritate the tick and can make it regurgitate into the wound, which is the one thing you are trying to avoid;
• clean the site afterwards and write down the date;
• watch the spot for several weeks. A spreading red mark, or fever, or aching joints, are reasons to see a doctor and to say there was a tick bite.