Most ticks know where you are in the woods. They, like many other arthropods, find you by your telltale carbon dioxide signal every time you exhale. Once they know you’re nearby, they hop onto the end of a leaf and wait, holding their tiny front legs in the air as if praising the heavens, and should you or any other animal pass by they’ll latch on for the ride.

Hyalomma ticks prefer a more active hunting method. They ID you by your chemical scent, but they can also recognize a potential host visually from up to 30 feet away and will run along the ground to chase them down. The vibrations you cause as you walk and the heat from your body help Hyalomma ticks track you, too. They’ll follow you for 10 minutes or even more, covering distances of up to about 325 feet. For reference, that’s more than 15,380 body lengths for an unfed female —a 5’5″ person would need to run nearly 190 miles to cover the same relative distance. But to be clear, Hyalomma ticks are not tiny: their bodies are around 0.256 inches long, which s about twice as large as most of the ticks you’re used to. These guys really earn the nickname “giant ticks.”

And the worst news? They’re spreading. The main species of concern, H. marginatum, used to live mainly around the Mediterranean. But as of this week there have been two found in the Netherlands, both in 2019, and earlier this year German scientists confirmed that imported Hyalomma ticks had survived winter there for the first time.

Apart from their terrifying hunting capabilities, the spread is concerning because Hyalomma ticks are disease vectors. They’re capable of carrying Crimean Congo hemorrhagic fever, which is exactly as bad as it sounds, as well as bacteria like Rickettsia aeschlimannii (a type of spotted fever), Babesia caballi, and Theileria annulata. Only the first bacterium in that list infects humans, while the other two infect horses and cattle, respectively. That’s not a reason not to care about them—infections from tick-borne diseases can cause massive losses for farmers (not to mention suffering for animals). None of the ticks found in northern Europe have carried Crimean Congo hemorrhagic fever, but several were positive for Rickettsia aeschlimannii.

Perhaps in part because of our warming planet, these ticks seem to be moving northward. They can catch rides on migratory birds, which have spread them into Germany, Hungary, and Russia so far. There’s some concern that the diseases Hyalomma ticks carry could soon follow, though it’s not clear how long that process might take.

For now, if you live in northern Europe and see one of these behemoths don’t just squish it: capture it and report it to your local public health authorities. Governments are now tracking Hyalomma’s spread as it moves northward, and they want all the information they can get. Ticks are no joke—and that goes double for the giant ones.