The most common and most likely answer to this crossword clue is the 8 letter word PROLIFIC
I've seen this crossword clue in The Guardian
P
R
O
L
I
F
I
C
More clues leading to the result PROLIFIC
- Fertile academic ringing large one in charge
- Not totally against abortion, one caught with many offspring
- Close to April I put in crop if ground is fertile
- Constantly reproducing, much like anti-abortionists, I see
- Being fertile for most of one’s life – I will be near 100
- Rank of copper taking lifer without hesitation in southern Ireland
- Rich for life, practically — I lead in commerce
- Replant or clip if very productive
- Being fertile for most of one’s existence, I should reach 100
- Rich Tory following iniquitous leader is constant in opposing reproductive rights
Buddy explains!

The straight part
We know that "Constantly reproducing" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case constantly reproducing = prolific.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PROLIFIC mean?
PROLIFIC adjective- Fertile; producing offspring or fruit in abundance — applied to plants producing fruit, animals producing young, etc.
- Similarly producing results or performing deeds in abundance
- Of a flower: from which another flower is produced.