Moisture ants (sometimes called Cornfield Ants or Lasius Ants are often seen during reproductive swarming in late summer and early autumn. Swarming occurs for about 2 to 7 days. Winged females, winged males, and nonwinged attending workers are seen at that time and can cause great concern for the homeowner.
The winged females are 5/16 inch long, full-bodied and honey coloured. Winged males are 1/8 inch long, slender and black. The workers are 1/8 inch long and reddish in colour. As the reproductives prepare to fly away to mate and establish new colonies many workers attend them. The flight may occur at the nesting site or the ants may walk a distance before flying. Winged ants are attracted to light and may be found at windows or skylights.
These ants nest in damp areas, usually in rotting wood. The appearance of the nest is similar to cardboard, and is made of the rotten materials where they live. They often nest under concrete slabs and find their way into buildings through cracks in the concrete during the mating period. They feed on dead and live insects and plant sap. They will care for aphids and feed on the excreted honeydew. Occasionally they enter the houses looking for sweet foods.
Moisture ants do no cause structural damage or attack people, pets or fabrics. They will hollow out severely rotted wood but do not create any damage beyond what was already caused by the rot.
Control measures vary depending on the circumstances but include correcting moisture problems, removing rotten wood, sealing cracks and holes and treating with appropriate pesticides.
Colonies can be eliminated when the nest site is located but spraying ant trails or flight sites will only provide temporary reductions in their numbers.