Except that apples can also be green, whereas great spotted woodpeckers are always a medium-sized woodpecker species. So 'the apple is red" implies at least a r

Except that apples can also be green, whereas great spotted woodpeckers are always a medium-sized woodpecker species. So 'the apple is red" implies at least a red variety of apples, never all apples, so "the" doesn't cover the whole group. But "the great spotted woodpecker is a medium-sized woodpecker" does cover the whole group (species). "The" can be either a definite or indefinite article, depending on context. That in turh changes "is" between equivalence and implication. "An apple is red" does not imply that "Red is an apple". Use of the indefinite article makes the non-equivalence clearer.