Ants

Pavement Ants (Tetramorium immigrans) are small, dark brown to black ants from 2.5 to 4 mm long. Originally from Europe, they were introduced to North America in the 1700s. They are now common across the continent, especially in urban areas where, as their name suggests, they nest beneath sidewalks, driveways, and building foundations. Colonies can contain thousands of workers and several queens, enabling them to grow and spread quickly. They are most active during spring and summer, often emerging from cracks in pavement to forage for food.

Pavement ants use pheromone to mark foraging routes that can extend several metres from the nest. They will gather a wide variety of foods including seeds, sweets, grease, and dead insects, but they feed in an unusual way. They cannot digest solid food directly. Instead, they feed it to their larvae, which digest it and then regurgitate the food as a liquid for the adult workers and queens.

These ants are known for their epic territorial battles: hundreds or thousands of workers from rival colonies will engage in massive, organized battles to defend or expand their territory. The conflicts can leave hundreds of dead ants right on sidewalks or driveways.

Western Thatching ants (Formica obscuripes) are native to North America. They build large, dome-shaped nests out of tiny bits of plant material (twigs, pine needles, grass). The mounds generally range in height from 2–40 cm, although taller ones are not uncommon. A colony can also extend as much as a metre below ground level and contain tens of thousands of workers.

To ensure their nests get maximum sunlight for warmth, they will kill plants that grow too close or begin to shade the mound. They do this by chewing the bark at the base of the plant and repeatedly spraying it with formic acid until it eventually dies.

When defending their nest or attacking prey, they bite and then spray formic acid from their abdomen into the wound. This potent chemical is a strong irritant that causes a painful, stinging sensation, serving as an effective defense against larger predators.

They are known to "farm" aphids, protecting them from predators in exchange for the honeydew, a sweet, sugary secretion the aphids produce after feeding on plant sap.