So you thought Russell Johnson started out on that OTHER island? Wrong-o, he started out here on Crab Island, in 1957, where he learned all the tricks the Professor later used with Gilligan, the Skipper, too, the Millionaire and his wife, Ginger an-nd Mary Ann.

Scientists become trapped on a shrinking island with intelligent, murderous giant crabs.

Quotes:
Karl: "We are unquestionably on the brink of a great discovery. It is not likely that that discovery will be of a pleasant nature."

Crab Monster: "So you have wounded me! I must grow a new claw, well and good, for I can do it in a day, but will you grow new lives when I have taken yours from you?"

Trivia:
In 1957 alone, B-movie impresario Roger Corman directed ten motion pictures. Attack of the Crab Monsters was one of these.

Questions no one can answer:
Shown as huge, clumsy creatures, just how does one of the monsters meticulously snip apart the vital radio components?

How do the crabs blow up the plane?

They have the power to generate intense, focused heat waves — why is this power never used against any of the humans once they become threatening?

What does the discovery of oil on the island have to do with anything?

Why methodically blow up the island to begin with? Ostensibly, to corner the surviving humans. But aren't they already stranded? Like, on an island?

And where are the crabs planning on living once they destroy their own home?

Also, when the island's been reduced to only a single remaining outcropping of rock, just what exactly is generating all that electricity coursing through the transmitter tower? Batteries?

No one can say, and Roger Corman isn't talking.
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https://www.youtube.com/watch?v=qvDf6xi5FiA