When you start digging in dirt, it’s no surprise to encounter subterranean creatures. When I started work on the north side of the Old Library property, I encountered quite a few animalcules that I assumed were centipedes or millipedes, but I didn’t know which. Googling “centipede vs. millipede” turned up several sites happy to enlighten me. This page explains it succinctly:
While centipedes have one pair of legs on every body segment, millipedes have two pairs of legs per segment, Live Science reports. The position of their legs is probably the easiest way to visually distinguish them from one another. Centipedes have legs that point away from their bodies, while millipede legs point down at the ground. Centipede legs are also typically longer than those of a millipede.
Beyond their appearance, you can also tell a centipede from a millipede by their behavior. If you uncover an unidentified many-legged creature under a log or pile of leaves and it scatters away, that would be a centipede, according to Live Science. If it rolls up into a ball and remains still, it’s a millipede.
When the animal is in motion (which they seem always to be), it’s impossible to tell how the legs are paired, so I look at what direction they point. If further in doubt, I put a finger in the animal’s path to see whether it will curl up. (I am careful to do this only when wearing gloves: a centipede bite can reportedly be as bad as a bee sting.)
In addition to these arthropods, when I was working around smilax roots I usually found dozens of tiny snails, all dead as far as I could tell (or if not dead, at least doing a very convincing job of playing possum). At least I thought they were snails; later I wondered if they might have been rolled-up millipedes, so when I encountered them again, I looked more closely: definitely snails!
On the south side of the property, I still see centipedes and millipedes but also many more earthworms. I’ve found out a little about earthworms as well but still have a lot more to learn. I haven’t paid close enough attention to them to try to identify specific species, but this would be interesting. According to the USDA, earthworms “provide channels for root growth,” so I suppose it’s no surprise to find them around the camphor roots I am pulling up. And I suppose I’m seeing just the tip of the iceberg, as the USDA site says that a square yard of temperate woodlands (a good description of the Old Library site) will have 100–500 earthworms.
I try to be considerate and inconvenience the worms as little as possible, and for the most part they just phlegmatically glide away, though perhaps with a justifiable air of reproach (“What? Not this again!). Some, however, leap frantically into elaborate contortions; there is something called a “jumping worm,” so perhaps they are this type. One day I kept turning up so many worms at once that I just started picking them up and dropping them in an already-cleared area where they would presumably be safe. I don’t suppose the worm’s tiny brain is capable of much thought, but if it were, I wonder what it would have thought about being abducted by aliens and then dropped into an arena full of other earthworms!
Earthworms pose even less threat than centipedes, but the other day I got into an ant bed, and I learned the hard way that the ant’s fight-or-flight reflex is rather different from an earthworm’s. At least I assume it was an ant that bit me on the top of my thigh. It was quite a shock, and I was surprised to feel the sting and then chills running all the way up to my eyebrows! No permanent harm was done—I can’t even see where the bite was—but I was a bit more cautious afterward to avoid the areas where I had disturbed ants.
Nothing underground, however, is anywhere near as bothersome as the insects above it. Although the only exposed parts of my body are my face, ears, and neck, and those are liberally coated with insect repellent, I am still plagued by gnats and mosquitoes buzzing around. My father used to claim that a hat would discourage gnats. That may be true of a broad-brimmed hat, but a ball cap just doesn’t get it, and I am constantly waving around my head and saying, “Go away!” As if that would do any good!
WalkThoughts 
I loved your use of the word ‘phlegmatically’!