Hi Alison, sorry for the slow response - just got back to this after a few weeks off. This species sometimes has a dark red head - if you look through the CNM images you will find one or two other sightings with similar coloured heads. I think it's likely that the head gets darker as the ant ages, eventually looking blackish - many ants start out with fairly light colours which get darker as they mature, particularly as they spend time out of the nest foraging in the daylight. Cheers, Jon