I know many words for animals are usually written in katakana in contemporary Japanese, even though kanji exist:
And it seems some very common domestic animals I don't seem to notice written in katakana:
Then there's some others I'm not sure about but have a hunch, including organisms that are not "animals":
- クモ spider
- ケヤキ zelkova (a kind of tree)
- 魚 fish
- 鳥 bird
- 馬 horse
- 牛 cow
Are there some patterns or rules of thumb I should learn? Wiktionary doesn't seem reliable enough to look up which variant to prefer, which other free resource is better, especially when my Japanese isn't good enough to use monolingual sources?
Is it something to do with very common terms being exceptions? Or domesticated vs undomesticated? Or general terms vs more specific terms closer to individual species? Are the rules the same for animals, insects, birds, fish, and plants?