Animals
It's always interesting to write about animals ... and other creatures.... but it's even more fun to choose one that people don't normally write about.
Again, research is essential and may even turn up items of interest you never knew before. Many less well known creatures have characters of their own. Remember, I am not guaranteeing markets for any of these. Apart from a factual article, you could have any one of these as the main character in a story, for adults or children. So, as well as the 'real' animals, this includes a selection of imaginary beasties.
mongoose
snails and slugs
frogs and toads
stingrays
bats
caterpillars
insects, bugs, beetles, spiders, cockroaches and various other 'creepie crawlies'
reptiles such as snakes, lizards, goannas, turtles, and of course the dinosaurs
hyenas, wolves, foxes, warthogs
goats, antelopes, reindeer
the sloth
mice, rats, rabbits
elephants
giraffes
polar bears
grizzlies
pandas
kangaroos, koalas, wombats, thylacines
vultures and crows and eagles
polecats. minks and ferrets
weasels, raccoons and possums
echidnas, porcupines, hedgehogs and shrews
any of the cat family - lion, tiger, leopard, cheetah, lynx, bobcat, caracal, puma, serval, ocelot, jaguar, panther
sea creatures such as whales, dolphins, dugongs, squid, sharks and all sorts of fishy beings
mermaids
gremlins
dragons
nymphs
centaurs
gargoyles
the sphinx
ghosts and spooks
vampires
werewolves
trolls, dwarves and elves