It is close to midnight as I enter the Finnish Museum of Natural History in Helsinki by a back door. I am on the hunt for a deadly spider.

As is fitting for a national institution, the museum boasts a significant collection of botanical, zoological, geological and palaeontological specimens from all around the world. But for more than 50 years, it has also been home to a thriving population of the Chilean recluse spider (Loxosceles laeta), widely considered to be the most venomous of its kind. And no one really knows how it got there.

Taxidermist Janne Granroth unlocks the door to the temporary exhibition space on the ground floor. A recent exhibition involved bringing some tree trunks into the room, he says. “This brought in a lot of insects and the spiders had a field day.”

The room is not currently open to the public and is being used as a storage space, filled with packing crates, foam board, picture frames and a menagerie of stuffed animals, including a buffalo, a couple of battling zebra, a springbok and an ostrich with its slender neck taped to a metal stand.

Granroth proceeds with confidence, opening a huge drawer and lifting up sheet after sheet of plasterboard, clambering over a pile of wooden planks and getting down on his knees to shine a light beneath a cupboard. I am more cautious. As I squeeze past an alpaca-like creature, I have mixed emotions, simultaneously impressed by the softness of its fur and troubled by the thought that the coat of a South American mammal might be a particularly suitable hang out for a Chilean recluse spider.