Is one who raises animals such as snakes, scorpions, and spiders—that are not harmful—sinful, under the pretext of hobby and learning about them?

Snakes, scorpions, and mice are among the fawasiq (harmful creatures) that Islamic law has commanded to be killed. It is not permissible to keep them merely for hobby or amusement, unless for a valid purpose, such as scientific experiments.

Scholars have differed regarding the permissibility of killing spiders. Some have stated that it is sunnah (recommended) to kill them because they are venomous creatures. Others have said that it is not sunnah. The evidence cited, which Abu Dawud narrated in his Marasil from Yazid ibn Marthad, from the Prophet (peace be upon him): "The spider is a devil transformed by Allah Almighty; whoever finds it, let him kill it," is weak. As for its web, it is pure, and it is sunnah to remove it from homes for cleanliness.

It is safer to avoid keeping spiders unless for a valid purpose, such as scientific experiments.