Mike wrote to the "Consult-Ant" with a number of questions about ants. I am going to try to answer each one in a separate post. For the original list of questions and links to all answers, visit here.
11) Are there some ant species that simply drink water and then other species that absorb it from the humidity of the air? Or do they all do both?
Your question reminded me of the movie Microcosmos, which contains some great footage of ants and other insects dealing with water. I'll throw the trailer below.
The second thing I thought of was communal peeing as a flood defense, where ants drink water and then run outside to "pee," removing excess water from their nests. You know you want to click the link and see it, so go ahead. I'll wait for you to come back.
Ants need water. Many drink water from drops and small puddles.
Ants can obtain moisture from a variety of sources, including food. Leafcutter ants and weaver ants obtain moisture from plant sap. Many ants tend aphids and other insects of the order Homoptera for liquid honeydew, which is full of water. Other ants visit extrafloral nectaries on plants for a source of sweet liquid.
Ants have also been shown to use "tools" to help them collect larger amounts of water and sweet liquids than they could carry in their crops. Harvester ants (Pogonomyrmex) have been known to toss sand into liquid food and then carry it back to their nest. Aphaenogaster ants use bits of plant material as sponges to soak up liquids and transport it.
Mark Moffett found Diacamma ants decorate their nests with feathers, which collect dew in the early morning. (I have seen Forelius ants carrying feathers here in Arizona.) He also suggests that the dead ants spread around the nest might also serve for dew collection.
As far as "absorbing humidity," Coenen-staß (1986) suggested that the red wood ant, Formica polyctena, might be able to absorb water vapor based on sorption rates. Other scientists have investigated desiccation resistance, and suggest that, for example, some ants can reclaim their internal water through structures called "rectal pads"(Hood and Tschinkel, 1990).
Videos showing ants drinking water:
Pay close attention to the rear section (metasoma or gaster). Look how it swells and becomes clear as the ant drinks.
Microcosmos trailer. For a review, see my Growing With Science blog.
The bottom line is that worker ants do drink water, and give it to other members of the colony. As for humidity absorption, that is relatively unknown.
For more information:
Coenen-staß, D. (1986). Investigations on the water balance in the red wood ant, Formica polyctena (Hymenoptera, formicidae): Workers, their larvae and pupae. Comparative Biochemistry and Physiology Part A: Physiology. 83 (1): 141-147.
Hood, G. and W.R. Tschinkel. (1990). Desiccation resistance in arboreal and terrestrial ants. Physiological Entomology, 15 (1): 23-35.
Moffett, M.W. 2010. Adventures Among Ants: A Global Safari with a Cast of Trillions. University of California Press, Berkeley.