These critters cannot be newly placed around the tree trunks, as shown, but must have had a newly planted small tree grow up within the loop. But Ed got hold of some by just lifting them off a still-immature tree, or perhaps felling a small tree. Monster!
Or do you have some kind of better explanation for this scene?
Comics I Don't Understand 
I think the post title is more accurate than the “realistic” paragraph below the comic. These are not traditional (inflatable plastic) pool toys, they grow naturally from the mythical “pool toy tree”. You can see the two trees from which they have been “harvested”, in the second row diagonally ahead of their parents. Presumably they can be sewn or fused back together after they have been excised.
P.S. Kanin often goes for surrealism, but this comic seems significantly “darker” than most of the others I’ve seen.
Kilby is right. Look at the tears rolling down their faces.
I was assuming the circle part of the float cannot harmlessly be opened and reclosed. Which would mean there is no way to get an individual off their tree “alive” unless the tree is cut off, or is still a small tree without large branches. And, reading-in more imagined natural history of these symbiotes, if the pool toys are born or hatched along with their trees, the occupant of an immature tree would be a child pool toy….
There is, of course, a non-zero positive chance that we’re overthinking this!
It’s what we do
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