My dad also grew up in a German speaking household speaking low German,or Niederdeutsch. His parents/grandparents came from the northern part of Germany. After I had lived for a few months in Germany in my early 20s, I could understand most of what he said, even though his dialect was different from the one where I stayed. It was a very interesting experience. It's intriguing that your mother's word for moth was so similar to the word for bat.