Carpenter Ants

Order: Hymenoptera
Family: Formicidae
Species: Camponotus spp.

Description and Life History: Ants, like many hymenopterans, have constricted abdomens and elbowed antennae. If wings are present, there is two pair. Ants are eusocial (meaning truly social) animals like termites, bees, some wasps and naked mole rats (!?!). They have a caste system consisting of queens, reproductive males, minor, intermediate and major workers. Carpenter ants in the Northwest range in size (6-18mm) and in color (red to brown to black), so color and size (as with most insects) are not good characteristics to use. Here at the office (especially during the spring) we get many costumers bringing in ants. So how the heck do you identify carpenter ants? There is a very user-friendly key to PNW ant species in the office (EB0671) written by our own WSU ant gurus, Drs. Akre and Antonelli. This key only works on wingless workers and winged females. You need to pull out the microscope to properly identify a carpenter ant (NEVER attempt to identify an ant without a microscope). In a nutshell, you will be looking for a circular fringe of hairs around the anus (this can sometimes be hard to see) in combination with a smooth (not notched) thorax. Presto! You have a carpenter ant. Yep, that’s right you’re looking for an ant’s hairy butt (life as a Master Gardener isn’t always glamorous).

During the spring, winged reproductive ants emerge and form mating swarms. Unfortunately, these are the ants that most people bring in, winged males. You need to have the customer fetch some worker ants too so you can identify them properly. The flight of reproductives can occur anytime between January and June (if you’re a fly fisherman, you know this already; an ant pattern can be a very productive fly pattern). Mated queens will then look for a place to nest. Many times this ‘satellite’ nest will be close to the parent colony. The queen will produce a brood of workers. Once the minor workers hatch into adults, they start excavate a colony and care for the queen while she kicks back and lays egg after egg after egg. Six to ten years later, another mating swarm will happen and start the whole thing over. Ants do not feed on wood but excavate nests out of damp rotten wood. The diet of ants consists of animal protein (mainly from insects), rotting fruit and aphid honeydew.

Monitoring: Ants prefer rotting, water damaged wood but sometimes carpenter ants will move into ‘good,’ treated wood too. Instead of going into a long tantrum of places to monitor, I’m going to refer you to a great website written by our other bug guru, Sharon Collman et al., http://gardening.wsu.edu/library/inse004/inse004.htm. Look for foraging ant trails and winged reproductives inside the house. Many times, ants forage for food inside the house but are not nesting in any of the wooden structures of the house. Also, winged individuals can be commonly found in windows but often these ants are incidental. If either ant types are found in large numbers, it’s time to start looking for the nest. Sure signs of carpenter ant infestations are piles of sawdust, crumbling wood, persistent ant trails and finally the noise of thousands of chewing ants that will drive you batty. Places to scout inside the house include: crawlspaces, attics, basements, ceilings and wall voids, basically, anywhere there is wood that is not in the main traffic area of your house.

Management: Don’t live in the woods! Most carpenter ant infestations occur in houses out in the county’s woodlots. If you do get an infestation, you not only need to locate and manage the colony inside the house but also manage colonies (most likely the parent colony) outside in the perimeter of the house to solve the problem. Most ant infestations are satellite colonies from mother colonies out in the yard. Finding infestations and local colonies can be difficult and may warrant a professional. Unless the colony is easily accessible and easily managed, I suggest hunting down a reputable pest control operator. Mainly because they can guarantee the work and are trained to effectively treat for infestations. Once the colony is managed, you can take many preventative measures to make sure this doesn’t happen again. Consult PNW Insect Control Handbook or EB0818 for information on boric acid or borates and suggestions for wood treatments. More importantly, increase ventilation in areas vulnerable for infestations to slow down wood rots. Rotting wood is ideal for infestation along with other problems. Inspect and clean woodpiles for ant colonies, and reconstruct (if necessary) your wood storage area so it is dry and spacious enough to get good air circulation. Do not use decorative stumps, stump planters, untreated railroad planks or driftwood in your landscape. Pick up potential food sources, such as rotting apples and manage aphid populations.

Even though there are no readily available biological controls yet, there are many fascinating critters already out there making life difficult for our carpenter ants. For example, the ‘decapitator fly’ does just that. The decapitator fly amazingly hovers over anthills like a helicopter waiting for the unsuspecting ant. Once the target is in sight, the fly flicks an egg that attaches to the back of the ant’s head! The egg hatches, and the maggot decapitates the ant and makes home inside the head capsule. Another fly called Microdon, related to hover flies, sneaks eggs into the nest in a similar fashion. The egg hatches inside the colony. The Microdon maggot leisurely feeds on the larvae of the ants. Normally, ants are extremely protective of their nest and young but the Microdon is able to trick the ants into thinking that its just one of the colony by its smell; the maggot mimics the pheromones of the ant. The ants even protect and nurture the maggot until it pupates and emerges as an adult. If this sparks your morbid curiosity, read Dr. Akre’s “Who’s eating the children”, American entomologist. 39, no. 4 (Winter 1993): p. 238-243.