Although every cactus I grow is the same, they are, of course, all different. It's the unusual that I particularly find interesting. Here is a page devoted to some of the unique characteristics and my names for them:
The Hoverflies that visit the flowers: There are very few bees and never any wasps, that are interested in visiting the flower of the cactus when it blooms. However, almost every flowering is accompanied by a visit from a hoverfly or two. Here's a couple snapped in August 2018 visiting the same flower, even having a little battle with each other to assume dominance. Looking for a hoverfly expert to identify the genus please.
And here's another, close up...
Leaf-Cutting Bee nearly every year the cacti in my greenhouse get a visit from a very interesting species of bee, one that doesn't live in a hive with thousands of other bees, nor does it seem to make honey...it's a leaf-cutting bee that makes a hole in the earth and brings pieces of leaf that it has cut into an arc shape, to bury in the earth, wrapping it's maggot-like offspring in cigar-shaped cocoons made from the leaf-pieces.
This is a relatively new phenomenon to me that only started happening to my cacti in 2016, possibly after being exposed to direct sunlight through a greenhouse window. The growth cells at the top of the cactus become scorched and burn away, leaving a hole in the cactus at the crown....
The result is that a new baby grows over the hole hence the name of "Crowning". Here's an example:
Turning Orange: I think that this is another response, like the above, to being scorched with concentrated sunlight. The flesh turns orange at first, later it goes brown and it then hardens and becomes wooden. Here's an example:
Flower Base Growth A new phenomenon that has only happened in Summer 2018; the base of a flower has stayed attached to the main cactus, after the body of the flower had withered. Is it that the flowered was pollinated? Nerds needed.
Other phenomenon will be explored further soon, these will include: Water-Towering