"An ant is an insect."
Translation:Une fourmi est un insecte.
How do you know whether something eg animal, insect, thing is masculine or feminine?
You memorise it. The best way is to just learn the noun with the article "une fourmi" = "an ant", "un insecte" = "an insect", "une pomme" = "an apple" rather than "fourmi" = "ant", "insecte" = "insect", "pomme" = "apple". Then if the article is "une", you know the noun is feminine, if it's "un" you know it's masculine.
There are some patterns in the endings, but there are always exceptions and it's safer to just learn it rather than relying on the ending to figure it out.
I thought that all ordinary ants would be male and only the queen could be female.
the only male ants are drones, they have wings and their only purpose is to mate with the queen and die. all "normal" ants are female.
When you hover your mouse over 'An', 'Un' is the first option shown, think Duo should switch these as I wrote 'Un' when it was feminine.
I would suggest NOT trusting duo on the first hint. It is very often for the first hint to mislead.