Maybe the insects in Columbia wear magnifying glasses. :-))

Interesting club shape to that one, was it etiolated at one point in its life?

It's always been in full sun so I don't think etoliation has ever been a problem.

Here's a link to my little blog about its life with me so far.

Here is a link that might be useful: Life of my Mammillaria columbiana

This cactus I bought for 50p was IDed as a possible columbiana-must admit yours does look very like an older version of mine!
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you can see it to the right in this pic;

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Nice plants, Larry. That little one does look very columbiana-like. I only recently got the ID for mine (here on this forum) and I think mine is more likely to be ssp yucatanensis rather than ssp columbiana.

I am told that this week it has now progressed to a ring of flowers, but unfortunately it will probably be all bloomed out by the time I see it.