How many letters does the top answer for “belonging to the same species” have?

The most common answer is conspecific (11 letters).

Crossword clue: belonging to the same species

1 answer found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

conspecific 11 letters wn-def

an organism belonging to the same species as another organism

of the same species. 67% similar → conspecific

belonging to the same genus 50% similar → congeneric, congenerous