It's all semantic nitpickery; my point was that Marxism was first devised in (and thus can be described as "of") the nineteenth century, whereas Nazism was first devised in (and thus is 'of') the twentieth.
As the old woman in East Berlin said to the American reporter after the Wall came down, "I have lived under Nazism, and I have lived under Communism, and the difference is: with Communism, the idea is nicer."
Communism is a lovely idea, but it requires "spherical workers of uniform density" — that is, it makes several idealized assumptions about human behavior, human nature, and human thought. If human nature was such that communism could actually work, we wouldn't need for it to be implemented, because that would be our natural state.
The reason that communism in the real world has only ever been applied by murderous tyrants is that, whenever anyone who's not a murderous tyrant tries to implement it, they only get so far before the population resists. And once the population is resisting, the leader can either stop (and thus not have communism), or brutally crush them. And any leader willing to brutally crush resistance to the implementation of communism is also willing to use brutality for all other purposes.
Communism doesn't cause murderous tyrants, it selects for them — a subtle distinction, and one which some would argue makes no difference.
That said, this is a significant derail. Whether what the spiders are doing really counts as "Marxist communism" is an interesting question; they think it does, but I don't know what a political scientist would say.