Spoiler alert
Is it true that the cause of the bridge collapsing is still unknown?
Were there any cultures that have “Mothman” in their mythology?
This time the IMDB comes to the rescue:
A fairly detailed account of the Silver Bridge collapse can be found here. Basically, the IMDB has it right: a structural element cracked, and the crack grew over time. Couple to this the fact that cars had gotten heavier in the forty years since the bridge was built, and the extra Christmas-season rush hour traffic, and its fate was sealed.
The Silver Bridge, pre-collapse. From a postcard.
http://www.rootsweb.com/~wvwags/silbr.jpg
Silver Bridge Collapse page
Disclaimer- I have not seen the movie. I was a big fan of the ufo/esp/cryptozoology section of the library as a teenager, and suspect that I’d spend a lot of time shouting at the screen.
Nobody who saw the whateveritwas* said it looked like a moth. The description was a grey humanoid figure with large wings, no visible head or neck, and glowing red eyes set in its chest. Early stories tried various names-birdman, big bird, batman etc. Mothman was settled on despite no description of the whatever having insectoid qualities.
To answer your question- What do you mean by Mothman? If you mean creatures with similar appearance, then some cultures do. If you mean creatures whose appearance portends coming disaster, then plenty of cultures do.
- Going by descriptions, many scientists concluded it was actually some kind of crane which wound up far out of its usual habitat. There is a verified case of lake monster sightings turning out to be an elephant seal who was far from home.