Back in October I wrote on the subject of the Kraken, stating rather emphatically and cantankerously that
whales eat squid. It is a unidirectional ecological interaction.
I received a very thoughtful response from one Daniel Rolph, who commented
I'm familar with 'whales eating squids,' and the discovery of 'beaks' of squids in their gullets, but I'm also curious about the statement made by the late biologist, Ivan T. Sanderson, who wrote among his many volumes, one entitled, 'FOLLOW THE WHALE,' which was all about the 'sperm whale.' He mentions the evidence of finding on sperm whales, huge 'circular sucker marks' of squids who'd fought the whales which were later caught, scars 18 inches across, implying a squid of 100's of feet in size (and not scars that had 'enlarged over time by the growth of the whale), but proof of actual conflicts between truly 'colossal squids' and sperm whales in the ocean's depth.

This, in turn, reminded me of the conclusion of Richard Ellis' The Search for the Giant Squid.
Have I been too quick to dismiss the unmeasured giants? . . . Perhaps, instead of categorically clinging to the closed system I have worked so hard to establish, I ought to end this book with an open mind. Maybe there are bigger giant squid out there, and maybe people have actually seen them. That they haven't been measured may not be all that important anyway. Can we dismiss every account that doesn't fall within our established guidelines?
I do agree that the vasty deep may still hold marvels well beyond our current imaginings, and 'tis important to remember this! However, though there is still a great deal we don't know about the deep sea, it is possible to make certain educated guesses. And as Ellis points out,
I'm only willing to include the 100-footers in this amendement; a 150- or 200-foot long monster would have a very difficult time finding enough food to keep it going and is still, I believe, in the realm of fantasy.
That there may be much larger squid than science currently reports, I'll readily concede. But that these squid, no matter how large, may actually attack and consume whales, I find nearly impossible to imagine.

I have outlined the reasons why squid, particularly the human-sized Humboldt squid, are extremely unlikely to kill and eat humans. I believe the same reasoning ought to apply to the likelihood of whale-sized squid killing and eating whales.

However, it's quite likely that enormous squid could inflict real damage on their predators while they struggle to escape--just as a zebra may get in a lucky kick, and break a lion's teeth. I just don't think any squid it its right mind would try to tangle with a whale on purpose.

The title, of course, is from King Henry IV, Part 1, Act 3 Scene I:

         I can call spirits from the vasty deep.

         Why, so can I, or so can any man;

         But will they come when you do call for them?