Camponotus: a portrait of the carpenter ant colony

A naturalist's view of the most architecturally accomplished insect that quietly shares your home.

Of all the ants a Quebec homeowner is likely to meet, the carpenter ant is the one most worth understanding. It is large, slow, deliberate, and quietly competent. The genus is Camponotus. Several species occur in Quebec, the most common being Camponotus pennsylvanicus, the black carpenter ant. A worker stands somewhere between six and thirteen millimetres long depending on caste — bigger than the pavement ant on your driveway, smaller than a wasp. Up close, it is a creature of considerable beauty: matte black, finely jointed, with a single nodal segment between its thorax and gaster and a small thin waist that distinguishes it from every other large insect you will see indoors.

An economy without a king

A carpenter ant colony is a single organism distributed across many bodies. The queen produces eggs. She does not rule. The workers, who are all sterile females, do the rest. They forage. They tend brood. They cut and shape the nest. They defend it when challenged. Their labour is divided by age — the youngest workers tend to younger brood, the oldest do the riskiest foraging — and they communicate through chemical trails, antennal contact, and the relative concentrations of dozens of pheromones whose meanings entomologists are still working out.

The colony's purpose is to produce more colonies. Most years it does not. It feeds, expands its galleries, and stores energy. In a year when conditions are right, usually a warm spring after a damp autumn, the colony produces winged males and winged females — the alates — and releases them in a single coordinated swarm. The males die within days of mating. The mated females, now queens, fly off to start their own colonies. Most fail. A few succeed. The species persists.

What they actually eat

A widespread misconception is that carpenter ants eat wood. They do not. They cannot digest cellulose. What they eat is what most insects eat — protein and sugars — and they find both in surprising places. In the wild, they tend aphids for honeydew, scavenge dead invertebrates, and harvest plant secretions. In a house, they will follow trails to pet food, syrup spills, fruit, cat food bowls, and grease deposits behind a stove. The wood they encounter is structural, not nutritional. They chew through it to make space.

The galleries they excavate are sometimes mistaken for termite work, but they are different. Carpenter ant galleries are clean, smooth, often follow the grain of the wood, and have a faintly polished look. There is no mud, no soil packed into the tunnel, no fecal pellets. There is instead a fine powder called frass — a mixture of wood shavings and the remains of dead colony members — which the workers periodically push out of the nest through small openings. If you find a small pile of what looks like sawdust at a baseboard with a few insect parts mixed in, you have found frass, and you have found a carpenter ant nest somewhere very close.

Why they need water

Carpenter ants do not excavate sound, dry wood. They prefer wood that has been pre-softened by moisture and partially decayed by fungi. This is one of the most reliable rules in entomology for predicting where they will be. A roof leak two stories above. A plumbing seep in a wall cavity that nobody noticed because the drywall on the room side never got wet. A foundation crack where snowmelt has been infiltrating since the building was built. The carpenter ants find these places. They make their galleries within the softened wood. The colony grows there for years, often without ever being seen, until something — usually a satellite colony or a foraging trail — gives them away.

This is also why treating the ants without addressing the moisture rarely lasts. The original conditions that drew them are still there. New queens will find the same wet wood next spring.

The polydomous trick

Carpenter ant colonies have a property uncommon among ants: they are polydomous. They maintain a single colony spread across multiple nests. The original nest, called the parent colony, contains the queen, the eggs, and the youngest brood. Satellite colonies — sometimes several of them, sometimes in the same building — hold mature larvae, pupae, and workers. The colony moves brood between nests as conditions shift. When the basement nest gets too cold in November, the workers move sensitive stages up into the warmer kitchen wall. When a satellite is disturbed, the colony absorbs it back into another nest.

This is the reason a single treatment in the basement does not always work. The basement nest may have been a satellite, not the parent. The queen lives somewhere else. The satellite gets killed; the colony notices; a new satellite is established within weeks.

The implication is that effective treatment must treat the colony, not the nest. Trail-following non-repellent products that workers carry back to feed nestmates are how this is achieved.

What they sound like

This is one of the small details that surprises people. In a quiet house at night, when the colony is at peak foraging activity, you can sometimes hear them. The sound is faint, like dry rice shifting against itself, coming from inside a wall. It is the workers moving in the gallery. It is not loud. You have to be paying attention. But once you have heard it, you do not mistake it for anything else.

Where they come from

Carpenter ants in Quebec are not invaders. They are native. They live in dead and decaying wood in forests, doing the work of decomposition along with fungi and termites in the regions where termites exist. When humans build wooden structures with moisture problems near forests, the ants do what they have done for millennia — they find the wet wood and they move in. Old neighborhoods with mature trees and old housing stock will always have carpenter ants present. The question is not whether they exist nearby. It is whether they have moved in.

Related reading: how to tell carpenter ants from pavement ants, why Outremont has so many, and the West Island pattern.

The takeaway

A carpenter ant in your house is a messenger. Somewhere in the structure, water has been doing damage for long enough that the wood has begun to soften. The ants would not be there otherwise. Treating the ants is the easy part. Finding the moisture, and stopping it, is the part that decides whether they come back.