Invasive Ant Removal

Argentine ants are considered to be one of the 100 worst alien invasive species on Earth. Over the past century, they have spread from their native range in South America to six continents and many islands around the world. In California, these ants have established super-colonies hundreds of miles long, stretching from San Diego to the Oregon border and beyond.

The ants are considered a major agricultural pest, and a nuisance when they invade homes. Where Argentine ants occur in conservation areas, most native ant species simply disappear, and that can have significant, cascading adverse ecological effects.

In the 1990s, researchers discovered that Argentine ants had established on Santa Cruz Island, the largest of the Channel Islands off the southern California coast. The island also harbors 33 species of native ants, the majority of which could be eliminated if the Argentine colonies were left unchecked. By 2010, the island had multiple documented infestations, totaling roughly 1000 acres, many of which were in dense vegetation and difficult to access terrain.

One aspect of Argentine ant biology that makes them so hard to control is that infestations comprise an extensive network of colonies. The ants we see are the foraging workers, and most pesticides on the market target and quickly kill them. But unless and until the queens of the colony are killed (and each nest has a succession of queens in waiting), the infestation would be able to rebound with ever more workers.  

Fortunately, those workers provided us the Achilles heel we needed: their job was to feed the queen.

What we needed was a way to get the workers to carry pesticide back to the queens. And that required innovation on a number of fronts.

It appears to have worked. But how can we be sure?

And after a series of applications, and careful follow up monitoring, our method appears to have worked. After just a couple years, we reached a point where we can no longer detect Argentine ants.

That lack of detection ushered in a whole new scientific question – and problem to solve. Does a lack of detection mean that they are actually gone, or only that they are at such low abundance they’re hard to find? If it’s the latter and we don’t detect and treat the residual colonies in time, we could easily lose all of the progress and investment to date.

But how to find such a tiny invader?

Our plan is to sniff them out. Working with expert dog handlers, we have trained dogs to detect Argentine ants, differentiating them from all the other ants they may encounter in the field. By running these conservation canines through the (formerly?) infested zone, we will be able to increase our confidence that the ants have indeed been eradicated from the island.

If the project is determined to be successful, it introduces yet another scientific challenge: how do we reduce the risk of Argentine ants stowing away on a boat or a plane and reinvading the island? That requires robust “biosecurity” protocols, implemented on the mainland as well as the island, aimed at keeping ant, weeds, and other pests and pathogens from gaining a foothold on this highly sensitive and unique island conservation area.