Like many of you, I’ve been working from home during the Coronavirus pandemic. The weather has been steadily warming, which means I’ve extended my home office to the back porch, away from the chaos and bustle of a busy family household. But outdoors has its own spring bustle, and I find myself distracted by the hum and buzz of busy pollinators, the to-and-fro of paper wasps, and the occasional ant investigating my snack crumbs.

Ants are, in fact, my favorite backyard residents. I love watching the pavement wars waged by competing Tetramorium colonies, or the endless trails of recruiting odorous house ants when they discover an unguarded morsel. However, my curiosity turned to alarm recently, when I spotted a crowd of large ants crowded beneath a rafter of my porch! What was going on up there? Upon closer inspection, I uncovered the bad news. Carpenter ants!

Winged carpenter ant reproductives

Winged carpenter ant reproductives emerging from the rafters of my porch.

The ants exiting from the timbers of my home had wings (pictured here). They were a batch of reproductives, emerging after overwintering within the nest, now ready to depart on their mating flight. After mating, they dispersed across the landscape, in search of their own little nook to start a colony. It doesn’t need to be much, just a small cavity with potential, usually in a stump, log or under bark. Sometimes, when we’re unlucky, they discover that spot in our home.

In a house, that might be a crevice where there was past termite or water damage and the wood is decayed and soft. Carpenter ants don’t eat wood, they excavate it as they expand their nest. When a newly mated queen selects her nest site, she breaks off her wings and lays her first eggs. This first batch of minor workers will later take care of her, and the queen can focus all her energy on reproducing. The development of a colony is slow and steady, growing from a few hundred workers in the early years, to as many as 10,000-50,000 workers in a mature colony. Bit by bit, workers continue excavating wood to expand their nest. This, of course, damages homes and other structures.

Camponotus modoc (by Alex Wild)

A carpenter ant (Camponotus modoc) commonly seen in Oregon (photo by Alex Wild)

Camponotus vicinus (by Alex Wild)

A carpenter ant (Camponotus vicinus) out foraging (Photo by Alex Wild)

Camponotus modoc (Stephen Hart)

Carpenter ant eat a wide variety of other insects in your yard (Photo by Stephen Hart)

Camponotus modoc (Sean McCann)

Camponotus modoc feed on the sugary honeydew produced by aphids
(Photo by Sean McCann)

Now, in May and June, is the time you’re going to notice carpenter ant activity, as workers hustle for food to support the rapidly growing larvae. There’s nothing for them to eat in the confines of your walls and attics, they need to forage outside for insects and other arthropods, and for the sugary honeydew they gather from aphids. You’re probably already familiar with your local carpenter ants. My entomologist friend Eleanor Spicer Rice describes them as “excellent ambassadors between the ant and human world.” They’re the largest ants around, easy to follow and watch as they amble along your cobblestones or climb up the trunk of your backyard oak tree. There are over 50 species in the genus Camponotus that are commonly called carpenter ants in North America, but there are really only two species that we that we think of as carpenter ant pests in the Pacific Northwest. Camponotus modoc and Camponotus vicinus are the villians responsible for most of the structural damage in our region. Both species can have large colonies of up to 50,000 to 100,000 individuals, and both have polymorphic workers, with minor and major workers ranging in length from 6mm to 13mm (that’s a big ant!). If you have an active carpenter ant colony nearby, you’re going to notice a lot of large, busy ants!

Camponotus modoc

Profile of Camponotus modoc. A common species of carpenter ant, characterized by a black body and red-brown legs.

Camponotus vicinus

Profile of Camponotus vicinus. Similar to C. modoc, but with by a red-brown thorax legs.

Carpenter ants don’t usually produce their first winged reproductives until the colony is between 6 and 10 years old. That means the queen of the colony that I spotted from the back porch moved in long before we started renting last winter. This is going to need a bigger fix than over the counter baits and plugging holes. A carpenter ant infestation is a problem best tackled by a professional pest management company. Here are a couple tips and resources to learn more about carpenter ants and prevent future infestations.

Prevention tips

  • Make sure spaces have proper ventilation to avoid moisture buildup
  • Inspect your attic, crawlspaces and walls and replace damaged wood
  • Repair leaks in roofs and gutters
  • Avoid letting plants grow in contact with exterior walls
  • Prevent wood-soil contact to avoid moisture damage or rotting
  • Stack wood away from structures and off the ground