The Fire Ants: Chapters 4-6

Anyone wade through chapters 4-6 of The Fire Ants yet? If so, let’s get started. (For those of you jumping in late, we are discussing the book a few chapters per week. Click “The Fire Ants Book Discussion” category for related posts.)

Chapter 4. A summary of the current thinking about where, when and how the various fire ants arrived in the southern United States from parts of Argentina and/or Brazil in South America.

Basically, it appears that one species of fire ant, Solenopsis richteri, was introduced to the port city of Mobile, Alabama area around 1918 and what we now know to be Solenopsis invicta showed up in the same area in the early 1930’s. At the time the two species were thought to be two color variants of the same species, and the lighter-colored Solenopsis invicta was called the “red imported fire ant.” It is interesting to ponder why the fire ants established only in Mobile, rather than in other nearby, and presumably similar, ports such as New Orleans and Pensacola.

The area of South America where Solenopsis invicta originated is also the home of several other migrant species of ants, including the Argentine ant, Linepithema humile, and my personal backyard “pet” ants, Brachymyrmex patagonicus, the rover ants.

In a way, this chapter is also about the formative years of E.O. Wilson, as well. Can you imagine the excitement/dismay of following the spread of Solenopsis invicta through your home state?

Does anyone have any more recent information to add? How about the genetic analysis of the central South American species? Are there any recent insights about the introduction/taxonomy that you would like to share?

Chapter 5. The historical spread of Solenopsis invicta and the eradication programs to eliminate it.

Time to admit a bias. I studied with W.L. Brown Jr. at Cornell, and he told about the mistakes of the fire ant eradication programs from the first week I arrived. He explained how using Mirex to kill fire ants had actually increased the rate the fire ants were able to spread. These days any pest management book or class will talk about pest resurgence, although at the time it seemed counter intuitive. How could a pesticide that killed a pest cause it to explode in numbers? Now we know that fire ants are a weedy species that thrive where other ants are knocked out, which is exactly what Mirex did. We killed the fire ants’ competitors for them.

Bill Brown wrote some of the early papers on the subject.

W.L. Brown Jr.  (1961). MASS INSECT CONTROL PROGRAMS:  FOUR CASE HISTORIES. Psyche. (click on link towards top for a free .pdf)

What do you think of the fact that Mirex was used in the 1970’s, only roughly a generation ago? Mirex is very persistant and moves through food chains like other chlorinated hydrocarbons.

Chapter 6. Where is Solenopsis invicta going in the future?

Maps are always fun.

This one is from 1982 by Strongbad at Wikipedia.

Map of the  status of Solenopsis invicta from Purdue.

In this case, the purple colors indicate establishment, green is areas that are fire ant free. Go to website for more information and yearly maps.

Tschinkel goes into quite a bit of detail about the biological requirements of Solenopsis invicta, and how that will probably limit their future distribution.

Tschinkel does not mention the effect of competing ants. Do you think that may be a factor in areas where the environment is marginal? What about Argentine ants in California? Is it going to be the battle of the South American ants instead of ant eradication by humans?

What are your thoughts on these chapters?

Let’s read Chapters 7-9 next, with the interludes. Tschinkel explores what a fire ant colony needs to survive: shelter, space and food. If you read nothing else, be sure to read the interlude, Mundane Methods on page 130.

I’m going slightly off topic. Blame it on too little sleep.

A few months ago when I first read these chapters, I had the distribution maps above and from the book on my mind.

Then I saw this map of the distribution of ADHD prevalence of treatment from the CDC (2003):

Comparing the purple areas above with the dark red areas here… I’m not saying fire ants cause ADHD… But, well, hum…. weird.

6 Replies to “The Fire Ants: Chapters 4-6”

  1. I just wanted to say that although I’m not reading the book (I’m reading “The Ants”), I really enjoy your presentation. Keep up the good work!

  2. You’ve inspired me to buckle down and read the book — And, it will be good to have done this before I see Walter next summer.

    Chapter 4 is important in pointing out a current area of interest among some who study invasive ants in North America, the importance of the native range of RIFA as a source for quite a few other invasive ants in the US SE. Questions arise as to whether this is a historical accident due to shipping routes, or is it something about the ecology of that fauna that spawns such aggressively colonizing species that seem so well made to live in Sun Belt, USA?

    Chapter 5 — I was a student of both Brown and Buren, but I also participated in research in Floirda on fire ant invasion post-pesticide. We started with uninvaded sandy and rather close-cropped pasture land. The short grass made surveying for all ant nests in the 1/8 acre study plots a lot easier. The plots were surveyed before treatment, and quarterly after treatment for two years. No fire ants were present in the treated plots before treatment, but half became dominated by them by the end of the study. Control plots had low numbers of fire ants at both the beginning and the end of the study. Plots that didn’t get taken over by fire ants after pesticiding where the driest and sandiest, less suitable for fire ants in any case, which prefer moist soil. We concluded that cleaning the ant community slate with Mirex or other formicides can indeed facilitate invasion or resurgence. One wonders how much Mirex is still around. We don’t hear about it much.

    Cahpter 6 — I have some doubts about the likelihood of fire ants invadingf all the “potential” areas that have been mapped. Lack of humid, hot summers such as in their native range and in the US Southeast may limit them, even more than it has Argentine ants, which do not stray far from irrigation or the light frost zone in the West.

  3. James,

    I’m glad reading the book is working out for you. I have to agree with your assessment of Chapter 6. Seems like Solenopsis invicta have had plenty of opportunities to seed into the drier areas of the Southwest, and they don’t seem to be.

    I do have a question for you. Although the main fire ants here in the Phoenix area have been identified as Solenopsis xyloni, the workers are more darkly colored than in other regions. Although coloration doesn’t seem to be a reliable taxonomic characteristic in ants, have you any thoughts on this?

  4. Re: Mirex

    Yes, it would be interesting to know what kind of monitoring is taking place and what the result are. Anyone have any information for us?

  5. Actually I’m out of the fire ant biz, now, so I don’t know about the monitoring question. But the color variation in S. xyloni is striking. Some are almost black, others almost as yellow as S. amblychila and aurea. But, this is actually true for S. invicta in South America, too. It’s just that we have a restricted gene pool of them here.
    BTW, I see the study I mentioned above in comments on Ch. 5 is cited as Stimac and Alves in the book.

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