Insects That Creap On The Ground
Even if an insect did not literally creep “upon the ground,” but was born in a fruit or vegetable while that fruit or vegetable was growing―the insect is still considered to to have been “on the ground,” since the item which it inhabited was “on the ground” 15.
If, however, an insect had never been alive on the ground nor inhabited a fruit or vegetable which was growing on the ground―it is permissible 16. Consequently, if an insect was born in a fruit that was already separated from the tree―that insect is permissible.
If that insect is removed from the fruit or vegetable it inhabited―it becomes an insect that “creeps upon the ground, ” and is prohibited. This applies, whether or not the insect was alive when it was removed from the fruit or vegetable.
An insect that is found in flour is prohibited, since it is suspected that, even if the insect was born in the flour, it may have left the flour and returned. This makes it an insect that did indeed “creep upon the ground.”
Insects that are found on the outside of a fish are prohibited, since they are assumed to have come from the outside.
By the same token, insects that are found in the intestines of a fish are prohibited, since they are assumed to have been swallowed and to have come from the outside 17.
On the other hand, insects that are found within the flesh of a fish, or between the skin and the flesh, are assumed to have been born inside the fish―and are permitted .
Is it not possible that an insect could have come from the outside, been swallowed by a fish and gone into the intestines of a fish―then migrated to the flesh of the fish? No. An insect cannot penetrate the intestines and travel through to the flesh 18.
However, if one purchased (or caught) a whole fish, and, in “cleaning” that fish mistakenly punctured the intestine―there could be an issue, since the worms may have been born outside the fish, entered the intestines, and may have gone into the flesh 19.