That's not the first time someone has made that sort of suggestion on some of my artwork as it happens. I seem to have a problem - or rather it's a weird issue where I find it very easy to distinguish dark colours from one another. So to my own eye the silhouette and black background have a high contrast. It's not my screen either (and I've been through a couple). I didn't have time to get proper opinions on it though.
I would say it's surely the screen. Not the type or quality of screen but simply the brightness one chooses.
As a print designer my screen is adjusted at the lower end of brightness because I want to see colors more like on paper, not glowing brightly.
When I put the brightness to medium (or more) the silhouette of your crawler is okay, but the yellow typo is burning out my pupils.
The other question is one of design.
For me the silhouette of your crawler is the visually most striking thing at this map.
So for me it's questionable, why the best thing is hidden in a dark brown to black contrast.
I would follow that if it's something with undead or so, but the topic of your crawler doesn't really dictate a dark coloring at all.
Background could be a light brown desert color as well. Just my two cents.
But aside that little point I like your crawler very much!
The whole idea is nice. What a bummer that you did not have more time to go a bit insane over it.