Here's why:
* Short vowel sounds are typically quick and sharp. Think of the sound you make when you say "uh-oh."
* Long vowel sounds are typically drawn out and can be represented with a single vowel letter followed by a silent 'e'. Think of the sound you make when you say "bee."
The vowel sound in "bug" is a short "u" sound, similar to the sound in "cup" or "fun." It's quick and sharp, making it a short vowel sound.