Scientists use Latin labels to classify animals, plants, and fungi into families, orders, classes, phyla, kingdoms etc.
Families of animals end in –idae, for example:
Felidae: the cat family
Equidae: horse, zebras asses
Hominidae: the family to which humans belong.
The classes of plants have the same ending, e.g. the class Asteridae.
I’ve always wondered where they got this –idae suffix from and what it means. Is it Greek or something, cos I know Latin pretty well and I don’t recognise it?
Could it be from the Greek suffix -idhs ? That is a patronymicon, meaning ‘child of’. It could make sense, but I’m not sure.
Yes. Taxonomists freely combine Latin and Greek roots and affixes in unspeakable and unnatural ways.
Anyone want to guess why the fem. plur. ending?
It’s not feminine. The ‐ιδης, ‐ιτης forms are masculine first declension nouns.
My approach 
From Greek eidos, meaning kind, sort, specie, genre. In latin it is transcribed the “ei” as “i”, I guess because around Cesar’s time it was spoken as “idos”.
THe plur. ending(?) comes also from Greek, exactly it is the neutral plural ending: ta astereidaia, again in Latin trasncribed as asteridaea → asteridae.
But maybe I am wrong…