Carpenter Ants: When to Worry

Client: “I think I have carpenter ants. Is it time to call the exterminator? Should I be worried? ”

Me: “Don’t panic. Let’s figure this out. What are you seeing and more importantly, where are you seeing activity?”

Carpenter ants are the most notorious ants for Nebraska homeowners, often called the “big black ants”. They are feared because they excavate their nests in wood, which cause damage to building materials to our homes. Carpenter ants, unlike termites, do not eat wood. As the name implies, these ants are carpenters. They carve tunnels in wood with their chewing mouthparts, creating smooth, sandpapered-like galleries. The wood that is scraped out is kicked out to form small piles of coarse sawdust. Take away: Carpenter ants do not eat wood.

Signs of carpenter ants: 

Just seeing a large ant outside in the landscape does not indicate an indoor infestation. However, there are several signs that indicate a carpenter may be located inside the structure and these include the following:

  • Piles of coarse sawdust with insect parts mixed (called frass)
  • Damaged wood with smooth galleries (no mud or soil packed in the spaces) 
  • Foraging worker(s) carrying food to a specific place and then disappearing.
  • Many winged ants indoors
  • Sound of crinkling cellophane in the walls 


Ants are easily identified by the fact that they have three visibly distinct body parts: Head, thorax, and abdomen (called a gaster in ants). The body part between the thorax and gaster is called the petiole, and ants have either one node or two nodes on this petiole. The main distinguishing feature that separates carpenter ants from other ants is that carpenter ants have one node and an evenly rounded thorax. Carpenter ants range in color from black to brown, red and even yellow, so color is not a good way to identify ants.

There are two species of carpenter ants commonly found in Nebraska, the black carpenter ant Camponotus pennsylvannicus and the red and black carpenter ant, Camponotus sayi. The black carpenter ant is a dull black color with long yellow hairs on its gaster. The red and black carpenter ant has a reddish-brown head and thorax with a black gaster. Workers range from 1/4-inch to 1/2-inch long. Carpenter ants queens are larger than 1/2-inch long and have three simple eyes between their two compound eyes on their large heads. 

Growth of a Colony  

Carpenter ants belong to the order Hymenoptera, which includes both social and solitary bees and wasps. All ants are social, which means they live in large colonies with overlapping generations, have a distinct division of labor, and collectively care for the young.  The formation of a colony starts with a single fertilized queen. The queen lays eggs and raises daughter worker ants, which help grow the colony and feed, raise, and protect the larvae and pupae. Carpenter ants are polymorphic, which means they have workers of varied sizes, called major and minor workers. Carpenter ant colonies could be a few thousand individuals to 15,000. After several years, the queen produces males and winged reproductives (called alates or swarmers) to disperse in a nuptial flight and start new colonies. After the swarming event, males die, and fertilized females lose their wings and become queen of the colony they produce. This is a seasonal and/or annual event, triggered by environmental conditions like temperature and rainfall. 

Food Sources and Foraging Activity 

Carpenter ants forage for solid and liquid food, carbohydrates, and protein. They feed on a variety of food sources including sugary honeydew secretions produced by plant pests like aphids and mealy bugs, plant exudates, other insects, and they scavenge on carcasses. Workers can only ingest liquid food sources, but larvae can convert solids into liquid food. Foraging ants will therefore feed the immobile, legless larvae solids and the larvae will regurgitate it back to the workers and allow it to be fed to the queen. This allows a mutual exchange of food, nutrients, and chemicals to flow throughout the colony. Ants antennate and groom one another constantly for caste recognition, communicate instructions and to protect the colony from pathogens. They are a true social colony that relies on the cooperation of all castes to survive.

Carpenter ants are nocturnal insects that forage at night between the hours of 10 PM to 2 AM. They follow structural and physical guidelines such tree branches, electrical wires, clothes lines, and edges of items. They lay down trail pheromone by dragging their gaster along the ground, to communicate to nestmates the location of food and are known to “waggle” as a form of recruitment. They can forage long distances, up to 100 yards (300 feet) from the nest, in search of food. The nest is where the queen will be with eggs, larvae, and pupae. Foragers will always take food back to the nest to share with nestmates.

Inspections for Nests 

Carpenter ants are known for having large, decentralized colonies called satellite colonies. Often the main or parent colony is located outdoors in moist, rotten, or decayed wood, and the satellite colonies are found in higher, drier areas inside or outdoors. Nests may be found in tree limbs, tree holes, stumps, firewood, logs, landscape timbers, living trees, dead trees, deck posts, porches, fence posts, structural members, foam insulation, hot tubes, crawlspaces, attic, roof overhangs, hollow doors, bay windows, bath traps, and chimneys. Carpenter ants do not kill live trees. Older trees may have a significant amount of decay due to excessive moisture, which ants take advantage of to easily excavate galleries. So, ants are a sign of dead wood, not the cause of death for a tree. Carpenter ant nests may extend into sound wood over time. Cutting down trees or filling cavities with cement is not advised, although some arborists may choose to treat the trunk. 

Integrated Pest Management for Homeowner 

When carpenter ant nests are found indoors it is usually a skylight, window frame, or door frame that has been damaged by water. This moisture damage makes this wood vulnerable to carpenter ant infestation and easy to exploit for nesting. One way to prevent carpenter ants from nesting in the structure is to manage the moisture to prevent the decay of wood.

  • Reduce sources of moisture which include areas of the roofs, leaky windows or skylights, poor grading around the foundation, full or faulty gutters and downspouts, condensation, or malfunctioning appliances.
  • Eliminate wood to soil contact. Do not stack firewood next to the building on the ground.
  • Provide adequate ventilation in crawlspaces, basements, and attics. 
  • Consider modifying the sprinkler system so water does not pool in vulnerable areas with wood products.

Another thing to do is to prevent entry into the structure by removing the pathways and bridges from outdoors.

  • Prune trees away from the structure so that they are not touching the roof.
  • Remove vegetative cover around foundation like vines and ivy.
  • Seal cracks and holes around the structure like utility entrances for wires and hoses.

The most successful treatments are those applied directed to the nest, but finding the nest may be challenging. One way to locate the nest is to follow an ant with food in its mandibles to see where it disappears. This area will also be where frass piles and winged ants are found.

  • Locate the nest and treat it with labeled insecticide. Replace damaged wood with new, pressure treated wood to prevent reinfestation by another colony.
  • Use bait labeled specifically for carpenter ants. Can be liquid, gel or solid granular, but must be attractive, palatable, and slow acting. Sugar-bait alone will not eliminate the colony due to the wide range of nutritional requirements.
  • Consider contacting a professional pest management company. They can treat the nest directly with special equipment and products. 

Circling back to the initial question “Should I be worried?” My answer is always “No”.

If you confirm that your specimens are indeed carpenter ants, investigate further. They may or may not be nesting inside your structural wood. If the nest is outdoors, exclude them. If the nest(s) are indoors, it can be treated. This is when you contact a professional to treat the carpenter ants.

All photos taken by Jody Green, who enjoys watching ants.


Hansen, L. D. and J. H. Klotz. 2005. Carpenter Ants of the United States and Canada.Comstock Publishing Associates.

Jody Green, PhD
Extension Urban Entomologist at Nebraska Extension
Jody Green is the extension urban entomologist at Nebraska Extension in Douglas-Sarpy Counties. She specializes in structural, household, and health-related insect pests.
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