Yes, ARMYWORM is a Scrabble word!

Letter values in Scrabble US: A 1, R 1, M 3, Y 4, W 4, O 1, R 1, M 3.

Is it a valid word?

ARMYWORM is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

noctuid moth larvae that travel in multitudes destroying especially grass and grain
moth whose destructive larvae travel in multitudes
larva of fungus gnat that feed on cereals and other grains; they march in large companies in regular order when the food is exhausted

Also: army worm, pseudaletia unipuncta.