The western boxelder bug (Boisea rubrolineata) feeds on the leaves, flowers and seedpods of the seed bearing boxelder tree. The adults are about ½ inch long and are black with three red lines dorsally. The abdomen is red.
They can become a pest outside when they cluster together on patios or walls and they sometimes enter homes and become a pest as they can spot curtains, furniture and clothing with their excrement. In the spring and fall you will generally find them on light colored surfaces on the south and west sides of a house, where they are resting in the sun.