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Tick, tock: Finland's ticks still thirst for blood

The bloodsucking parasites remain active well into autumn, scientists say.

Jani Sormunen poimii punkkeja lakanalta.
Researcher Jani Sormunen inspecting his tick catch following a sweep. Image: Minna Rosvall / Yle

Turku University tick researcher Jari Sormunen told Yle that people don't always realise that ticks still bite when the weather cools.

“[Small] nymphs are more dangerous in the sense that they’re more difficult to see. Larger individuals on average carry more harmful bacteria and viruses, but they’re easier to spot,” said Sormunen, who scraped 25 separate areas for ticks in Turku and 11 in Helsinki this past summer, covering over 100 kilometres.

Ruissalo in the Turku archipelago has the highest density of ticks in the Turku area. Sormunen's tick research is now expanding to include Oulu, Tampere, Jyväskylä and Joensuu.

“This summer we’ve collected an average of 15 nymphs per 100 square metre area, with that number rising to 25 in the peak month of August,” he explained.

No safe place

Early summer, between May and June, is the year's first high season for hungry ticks. The blood-sucking arachnids calm down in July but are ready for another feeding frenzy in August and September.

Sormunen told Yle that while most residents watch out for ticks in the forest, few people are on the lookout for the eight-legged creature in urban parks.

“There’s no typical place for ticks to inhabit, though they do seem to prefer damp, shady places with regular access to suitable hosts,” Sormunen added.

Dormant, not dead

The incidence of ticks at all of Turku University’s research sites in Turku as well as in Helsinki has risen over the past 20 years.

Southwestern Finland and Uusimaa have reported 29 cases of tick-borne encephalitis in 2019, according to health watchdog THL's infectious disease database. So far this year, some 1,500 people nationwide have contracted Lyme disease, an illness caused by ticks carrying Borrelia burgdorferi.

Sormunen said cold weather doesn’t necessarily kill off ticks, especially as the snow cover can protect them from winter's harshest elements.

“We once froze ticks down to -20 degrees Celsius in the lab, and when we thawed them up they were still alive,” he explained, adding that he suspected that the ticks had managed to slip into hibernation during the freezing process.

EDIT: This story has been updated to correctly state the number of legs ticks have.

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