Is it permissible to eat crabs and lobsters?
Before I answer your question, I’ll elaborate on a few premises.
It needs to be appreciated that the Almighty has blessed man with guidance in two ways. One of them can be termed as Innate Guidance and the other one as Divine Guidance.
As far as the sphere of Innate Guidance is concerned, it is known that man has been given certain faculties and abilities which are enough to guide him in deciding the right course of action. He does not basically need any external guidance in this regard. For example, his conscience very ably guides him about good and evil.
The second sphere of guidance, Divine Guidance, generally pertains to areas where human beings are unable to decide the right course by themselves. It is in order to complement and supplement the sphere of Innate Guidance that the Almighty has divinely guided man through His Prophets. The Qur’ān and Sunnah (the established religious practice of the Prophet (sws)) are the only original sources of Divine Guidance.
As far as edibles are concerned, Divine Guidance has prohibited some distinct types of food because they negatively influence the inner purification of a person. The rest has been left to human nature to decide for itself in view of the Innate Guidance it possesses. Man knows for himself that beasts like lions and dogs and birds like eagles and vultures are not meant to be eaten. There may be slight differences in this sphere, but generally the dividing line is quite clear.
In the light of this principle, a Muslim can eat crabs or a lobster if he does not feel an aversion to them. In other words, he himself must decide on this issue since we have no explicit prohibition in Divine Guidance on these types of foods.