They are quite small. Here’s one stroking Abraham Lincoln’s cheek.

You can also see the juvenile coloration — the adults wil be solid black, with just a red mark on the ventral abdomen. One thing I noticed was that when I put them in a container with a jumble of moss, they practically disappear, even with the bright red markings. More than once I transferred a spider to a new container and lost it, and had to poke around to be sure I hadn’t accidentally set it free on the lab bench.