Does the bright red tibia help identify it (see the other photo)? I notice the bugguide photos of M. sanguinipes have it, whereas those of M. devastator do not. Also, M. Sanguinipes reports are numerous from the northern Olympic peninsula (assuming they are correctly identified). I also note that the red tibia seem to be associated with males. Could this be a male?

Definitely a female, you can clearly see the ovipositor (four valves forming a point on the tip of the abdomen) in one of the pictures. Also, the stocky form jives more with females. Both species can have hind tibiae of several colors, but blue does seem to be most common in M. devastator. [Interestingly one popular guide - Helfer's - mentions only "red to grayish" for M. devastator.] The tibia color in M. sanguinipes is all over the place (brown, yellow, green, blue, purple, orange, red, pink, etc.), but red and blue are most common. I've even seen rare individuals with one hind tibia one color and the other another (I guess it's sort of like people's eyes that way). The color doesn't relate to gender (as far as I know, though percentages might be different for males and females in some populations?). I think it is just a chance artifact of random sampling that more males seem to be red in the photos. Here, where I live, both males and females of M. sanguinipes usually have blue hind tibiae. The stocky form and contrasting pattern remind me of M. devastator, but other details of the pattern look more like M. sanguinipes to me, and I do think that the later is the more likely identity.