Sci-Fi/ Horror flick seen on Saturday afternoon in 70s but the movie might be older with plesiosaur-looking monsters (loch Ness monster shape) but only as big as a man and they crawled on belly. There were many, and it seemed like an invasion. One scene a monster drops out of a tree onto a man–possibly in uniform.
“Island of Terror” (1966)??
https://www.imdb.com/title/tt0060548/?ref_=fn_al_tt_2
That’s the one! Well done!
Thank you jamesh.
Solved!