The Argentine ant is one of a gazillion non-native species that have been labeled “invasive species.” Like most non-native species, they are considered aggressive competitors of native ants. The usual tools are employed to eradicate them, e.g., pesticides.
But wait! Now scientists are suddenly noticing that the Argentine ant is disappearing from some of their colonial haunts. Scientists in New Zealand have recently reported the disappearance of the Argentine ant from 40% of sites they populated in the past and their populations have shrunk significantly where they are still found. Native ants have “reinvaded” the areas vacated by the Argentine ant. The scientists reporting this finding “concluded the species naturally collapses after 10 to 20 years.”
The scientists in New Zealand don’t claim to know why the populations of Argentine ant have disappeared. They speculate that a virus is to blame. They don’t claim “pest control” deserves credit for the disappearance which is estimated to have cost $53 million (NZ$68) per year since the Argentine ant was originally found there in 1990. That’s right, New Zealand spent approximately $53 million per year trying to eradicate the Argentine ant, which apparently is disappearing on its own.
This is apparently not an isolated phenomenon. An entomologist at UC Davis reports that the Argentine ant has been declining in California as well. How much pesticide was poured on Argentine ants before they showed the good grace to just disappear?
The Africanized Bee: Another scary story that didn’t materialize
Another example of an “invasion” that seems to have resolved itself is the Africanized bee. Do you remember about 15 years ago when the media created a panic about the Africanized bee? We were told that it was spreading rapidly from Latin America, headed our way and that it was so dangerous that it was capable of swarming people and animals and stinging them to death!
What happened to that particular “alien invasion” story? Professor Gordon Frankie (UC Berkeley), our local expert about bees, was asked that question in a lecture he was giving to Cal Alumni in October 2011. He said that the Africanized bee didn’t turn out to be as aggressive as it was originally thought to be and that it didn’t spread as far or as fast as predicted.
Does “Invasion Biology” make more problems than it solves?
Some months ago we created a Google alert for “invasive species.” Now we are treated to a daily barrage of scary “alien invasion” stories from all over the world. We wonder how many of these “invasions” will eventually prove to be benign. We wonder how much money will be spent, how many animals will be killed, how much pesticide will be poured on our public lands, before we figure out that we need not be afraid of everything that is new in the environment. We wonder how many people are making their living on these eradication efforts and what role they play in frightening the public into funding their projects and tolerating the destruction they inflict on the environment.
Conservation Sense and Nonsense 
i have been thinking why oooh why, what is their reasoning. I will keep your examples in my mind the ant and wasp did not need us to interfere.
I have been keeping a close eye on Japanese Knotweed here in my village, one of the plants on the list in the UK to be controlled. Yet it has not spread by much here on this particular spot. It appears on a spot where trees have been cut so little competition. i wonder if i plant a tree there what will happen? The village has not used any herbicides here, lucky as it lays right next to a flowing creek and it would kill more than Japanese Knotweed. Perhaps a good selection of plants and no mono-culture could be an answer to stimulate natural competition which would limit ‘invasion’ naturally.
Webmaster: Yes, you are definitely on the right track with your assessment and your remedy. Most “invasions” occur when there is a vacuum. Nature hates a vacuum. New species are therefore most likely to occupy land that has just been cleared. So, yes, study what this knotwood needs. If it needs full sun to keep growing, then a tree that would create shade seems like a good choice.
http://www.landcareresearch.co.nz/news/release.asp?Ne_ID=319
Webmaster: Thanks for this link to an article that speculates that the Argentine ant hasn’t “disappeared” from some places in New Zealand, but has just moved elsewhere. Current location not known or at least not mentioned in this article.