A Briton was arrested with two suitcases containing 1,000 live spiders at Rio airport, police in Brazil said.
The man, who has not been named, was stopped by federal police officers and agents from the Brazilian Institute for Environment and Renewable Resources.
He could face a fine of up to 4 million reais (£1.39 million).
The spiders were taken to National Museum where they will be examined by experts and catalogued according to species.
The man was arrested on Wednesday.
A Foreign Office spokeswoman said it had not been informed of the arrest.