I'm Japanese and we habitually use katakana in for the kind/species of animals, fish, plants, flowers, vegetables, fruits, etc, for example, キツネ、アジ、サクラ、バラ、ナス、リンゴ、etc. Since I'm not an expart of the Japanese language, I don't know why we use katakana for them though they are Japanese word. There might be histories for that, so please wait for the correct answer. Anyways, I hope this was helpful.

Words from foreign languages imported into Japanese (referred to as Gairaigo/外来語) are just one of the things katakana is used for. There are various other uses as well - like the names of some animals. See http://japanese.stackexchange.com/questions/20840/why-are-the-names-of-plants-and-animals-often-written-in-katakana for further information, and https://en.wikipedia.org/wiki/Katakana#Usage for the uses of katakana.

I'm not sure if it is the same but often words in katakana are derived from German/Dutch as they were some of the first nationalities who travelled to Japan. It's much like the word　アルバイト or Arubaito which is Part Time Job in Japanese. This was taken from the German word Arbeit. I hope that helps

Katakana is used for loanwords. Loanwords from every language, not only English. So it's probably another language.