Recommendations please: Old animal horror movies, ca. 1970 to 1989, WITHOUT "Happy End"

Hi folks,
I like very much those old (and sometimes unintentionally crappy / funny) animal horror movies which had their heyday during the 1970s, early 1980s... for instance, It happened at Lakewood Manor aka Ants; Piranhas; Kingdom of the Spiders, etc. - of course the classics like Jaws (which is definitely NOT a B-movie :-) too.
What I'm especially searching for is this: Do you know any movies of this style where there is NO "Happy End"? To define what I understand by the term: Even if there are just one or two survivors, that's not what I'm after - I just watched Kingdom of the Spiders (CAUTION: Spoiler!) where the last survivors find that they are trapped in the house, with no chance to get away from there, and spiderwebs cover the whole landscape; THAT's the kind of bleak and depressing end of movie which I would prefer ;-)
Another scenario would be a group of people on a lonesome island, getting killed one by one, to the last one - WITHOUT the usual scenes towards the end when the army, navy, whoever rushes in, kills off the beasts and takes care of the last survivors...
I think the movie Frogs does actually fit into my "scheme" - but I haven't got it in my collection; I only remember that it was broadcast on TV here, years ago... didn't the animals kill them all? Or did someone get away?
As to the species of animals, I'm not so much interested in oversized monsters. I would prefer to see normal-sized animals which have turned against the humans; giant mutations aren't so much of interest for me.
I think even such a classic movie like The Birds had no definite "message" that mankind is doomed; if my memory is correct Hitchcock left it open to speculation what may have happened after the final credits... Maybe or maybe not the phenomenon of birds becoming aggressive remained local... but if it doesn't, then - Game over ;-)
Kind regards
Andreas (123all4me)