Here's an update / alternative to the Spider-Man lemmings at last:In order to distinguish regular lemmings from athletes, I just gave the regular lemmings their green hair back, whereas the athlete's hair is red, as it used to be (see the Glider on the right).
In practice, this looks like a lemming gaining any athlete "super powers" dons his Spider-Man mask so he can start moving around the level parkour!
In the screenshot, you can see what it looks like when athletes are moving within a crowd. I think they're easy enough to spot.
The side effect of this is that the lemmings on the skill panel have green hair, too, instead of looking like Spider-Man with his head entirely covered - because the lemmings on the skill panel always look like the regular Walkers of a given sprite set (including those skills which are actually athletes in practice).
Simply drop this modified theme file into your strato_lems_spider-man folder to replace the old one if you want to.
If you prefer all the lems to look like Spider-Man all the times (i.e. with no green hair to be seen), including those on the skill panel, leave it as it is.