Wood Ant
Formica perpilosa
Psyllid bugs on Fremont Cottonwood with Formica ant. Hassayampa Preserve, Wickenburg, Arizona, 13 April 2014. Tentative identification provided by Dr. James Trager.
Formicidae -- Ant Family
Formica ants can release acid in a fine spray from the abdomen tip - chemists later named this acid Formic Acid (HCOOH). It is a very effective defense against birds and reptiles that might want to prey on them. Here the ant is using the same defense to protect a colony of sap-sucking psyllid bugs. The sap in the twigs from this cottonwood is high in sugar, enough so that the bugs share it with the ants in return for protection. While I was watching this group a Minute Pirate Bug, Orius, came to prey on the psyllids and was repelled immediately by the ant.