Why did people call tigers "big insects" in ancient times?

The ancients used "worm" to refer to all animals in general, and divided insects into five categories:

Birds are feather insects, beasts are caterpillars, turtles are beetles, fish are scale insects, and man-made insects are Bugs.

"大" means long (zhǎng) and leader, such as calling the number one among brothers "eldest brother"; "大" is also an honorific term, such as calling "adult" or "doctor" " King" etc. The tiger belongs to the caterpillar class and is the king of beasts.

The ancients matched the leader of the "five insects" with the directions of the five elements, and the god of the west was the white tiger. "Big Bug" means the leader of caterpillars and the king of beasts. This has the same meaning as the dragon in the east is the leader of scale insects, and the phoenix in the south is the king of feather insects and is called the "Dragon King" or "Phoenix" ("Phoenix" was only created in the Southern and Northern Dynasties)