Pseudomyrmex Ant of the Swollen Thorn Acacia

Pseudomyrmex ferruginea

Description:

Pseudomyrmex ferruginea is one of several species of tiny ants that are obligatory symbionts of the Swollen Thorn Acacias of southern Mexico and Central America. They are only about 3 to 4 mm in length and never leave the Acacia plant. They patrol the entire plant continuously and voraciously attack anything that bothers the Acacia, whether it be a herbivore, ant predator or an invading vine. The Swollen Thorn Acacias are completely dependent on their ant populations and do not survive in nature if they lose their ants. The plant keeps its tiny police force happy by giving them a home, food for the adults and food for the larvae. The thorns are more or less hollow and when they are still green, they are soft enough for the ants to make a hole in the thorn (one is visible in the last picture, upper right thorn) and hollow it out completely to use as a nursery. The adult ants are supplied high carbohydrate nectar from tiny little nectaries at the base of the plant leaves. The nectaries are unique to each species of Acacia. In this case, the nectaries of Acacia cornigera are canoe-shaped, oval and somewhat raised. In the first picture an ant is feeding at the nectary. For the larvae, the plant produces a high protein and carbohydrate food called Beltian Bodies. These are usually yellow to orange and grow on the tips of each leaflet. The ants collect these and take them into the thorn nests. The Beltian Bodies are not visible in these pictures, it is possible that the plant produces them in conjunction with the reproduction periods of the ants. See https://www.projectnoah.org/spottings/13... for pictures of the Beltian Bodies in the month of December.

Habitat:

A small Acacia bush growing along the San Viciente River, Chiflón Waterfall Park, Chiapas, Mexico. The ants are so small that they are not at first noticeable, but give the tree a few sharp taps on the branches and within seconds the tree will be covered in ants.