What should I do with a female spider and her hundreds of offspring that I put in a plastic box? Is it permissible to raise them, or should they be killed? And if killing is obligatory, what is the appropriate method for that?

If there is benefit or advantage in breeding insects and reptiles, such as conducting scientific experiments on them, provided there is no harm from them, then there is no objection to breeding them. It is not permissible to kill an animal that is not harmful. However, if it is harmful, it is permissible to kill it by the easiest means that takes its life, such as cold water, but not by burning or hot water.