A dangerous yellow sac spider (Cheiracanthium punctorium) is actively colonizing new areas near Helsinki. According to the publication Suomen Luonto, the species was spotted this summer on the Porkkala Peninsula in Kirkkonummi—significantly further east than its previously known range in the country.
This species first appeared in Finland in 2022, when it was discovered on the island of Seili. Since then, the population has been steadily spreading along the southwestern coast and moving inland, utilizing a method known as “ballooning”—traveling through the air on strands of silk.
By the end of summer 2026, the spiders had reached the Porkkala Peninsula. Currently, the species’ confirmed range is limited to southern Finland—specifically the area south of the line connecting Naantali and Porkkala. However, scientists note that a warming climate is working in the spider’s favor, allowing it to advance further north.
In terms of toxicity, it is the most dangerous spider in the local fauna, significantly surpassing other Cheiracanthium species found in Finland. Research by European biologists indicates that its venom contains components acting at the cellular level, triggering a potent inflammatory response in the body.
A bite causes acute pain comparable to a wasp sting. The venom can cause severe swelling and, in hypersensitive individuals, nausea and systemic reactions. However, the spiders themselves are not aggressive; they use their venom only for defense—for instance, if accidentally crushed or handled.
Experts warn that during the day, the spider hides in dense silk retreats woven into tall grass or thickets of shrubs. Females exhibit the greatest aggression when defending their egg cocoons, which measure about four centimeters in size.
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