Japan, a country known for its diverse natural landscapes, is home to a variety of spider species, inhabiting both urban and rural environments across the archipelago. While widespread, the vast majority of species encountered pose no threat to humans.
Common Spider Species in Japan
The Joro spider (Trichonephila clavata) is an orb-weaver known for its large golden webs. Females are notably larger and more colorful than males, measuring 17-25 mm in body length with a leg span up to 10 cm. Their bodies display vibrant yellow and black markings, often with a distinctive pattern on their abdomen, while males are smaller and brownish. These spiders are not aggressive and are commonly found in forests and populated areas.
The Japanese huntsman spider (Heteropoda venatoria), also known as ashidakagumo, is frequently encountered, particularly inside homes. This large, fast-moving spider does not build webs but actively hunts insects. Females can reach a body length of 2.5-3 cm, with a leg span extending up to 10-12 cm, capable of covering an adult’s palm. Huntsman spiders are beneficial for pest control in residences and are not dangerous to humans.
The wasp spider (Argiope bruennichi) is a common and identifiable species. Its female has a distinctive appearance resembling a wasp, with a yellow and white patterned body and a zigzag pattern in its web. These spiders are small, with females measuring just over half an inch, and are neither dangerous nor aggressive towards humans.
The Japanese funnel-web spider (Macrothele gigas) is a large funnel-web spider, distinguished by its black body and red fangs. With a leg span up to 15 cm, this species is primarily found in the Ryukyu Islands. While venomous and potentially medically significant, encounters are rare as they typically build tube-webs in the ground or under rocks and are not aggressive unless provoked.
Understanding Spider Bites and Safety
Most spider bites in Japan are not medically significant, often comparable to a bee sting. A typical bite causes localized redness, swelling, and mild pain. For minor bites, clean the affected area with mild soap and water, apply antibiotic ointment, and use a cool compress to alleviate symptoms and prevent infection. Over-the-counter pain relievers or antihistamines can help with discomfort and itchiness.
One notable exception is the Redback spider (Latrodectus hasseltii), an introduced species from Australia, which is one of the few spiders in Japan with medically significant venom. Redback spiders are black with a distinct red or orange stripe on their abdomen. Though not aggressive, they often inhabit areas close to human environments.
Bites can cause severe pain, muscle cramps, sweating, nausea, and vomiting. More widespread symptoms like abdominal or chest pain, fever, and changes in heart rate or blood pressure may occur. First identified in Japan in 1995, its distribution has expanded.
If bitten by a Redback spider, or if severe symptoms develop from any spider bite, immediate medical attention should be sought. Antivenom is available for severe envenomation.
Where Spiders are Found in Japan
Spiders are widely distributed across Japan, inhabiting diverse environments ranging from dense forests and mountainous regions to cultivated rice fields and coastal areas. They are also common in urban settings, including parks, gardens, and inside homes.
Spiders are more noticeable during warmer months and into autumn, often considered “spider season” due to increased activity and larger webs. Within homes, spiders often seek shelter and food sources like cockroaches. To minimize indoor encounters:
Maintain a clean living space and reduce clutter to help eliminate their food sources and hiding spots.
Seal gaps around windows, doors, and utility entry points to prevent them from entering.
Use natural repellents like citrus oil, peppermint, or vinegar sprays near entry points to deter spiders.