Yes.B. Pensylvanicus is common bumble bee in this area. I am just confused by the size. I saw about 6-7 bumble bees today and all were smaller in size.

Thanks.

Males are often smaller; here in Seattle we're mostly seeing males of our common late species, and the larger bees we're seeing are nearly all late generation workers. Size varies across colony age.

Thank you Dr. Kelsey for clarifying :)

this looks like a female worker which can be even smaller than the male (watch me be wrong about everything)

A worker

Early workers (from the first few eggs the queen lays) can be extremely tiny - smaller than honeybees by a lot. I have a whole range of sizes in my freezer from commercial Bombus impatiens hives that we've used for research, since we can't release them (and shouldn't, lest they bring parasites and the like into the wild). Some of the biggest workers late in a healthy colony's life can be as large as a queen, too.