Saturday, January 24, 2009

Fire Ants Attack - Lizards Adapt

Fire ants (Solenopsis) are an invasive species in the US, and they’re a big problem here in Florida – there are no less than two nests in my backyard at any given time. Their hunger for new territory and their proclivity towards violence has resulted in conflict on more than one occasion. Although, thousands have been slain locally (and righteously, in my view) the battles are ongoing – and I have more than one scar on my legs and feet to attest to this brutal history!

I’ve battled Solenopsis not for glory, but for the safety of the other backyard fauna; massacred frogs, fledgling birds and anoles have all been discovered – Kitsune and Zita (my dogs) have also endured the wrath and sting of these imperialists…

OK, OK – I’ll stop with the war metaphor.

In all seriousness these gals are hardy to say the least. My understanding is that their rate of expansion into North America is driven by a genetic discrepancy between the invading lineages and those native to South America that has resulted in social polymorphism. In Argentina, Solenopsis queens emit a pheromone that identifies her to the colony – make way for the queen! If a foreign queen should enter the colony, workers detect the foreign pheromone and quickly dispatch her (essentially she’s drawn and quartered). In contrast, a genetic mutation in the DNA of the US invasive variety has altered a pheromone binding protein (Gp-9) to such extent that invasive queens are no longer recognized by workers. Because of this, a single colony in the US may have multiple reproductive queens (polygyny) coexisting at the same time – reproductive rates go through the roof.

{This pic shows the colony "rafting" following flooding}

The pheromone recognition behavior, when functioning, has the affect of geographically limiting the proximity of any two colonies. This results in fewer individual colonies per a given area. When, due to mutation, foreign queens aren’t recognized, inter-colony conflicts don’t occur as frequently thereby opening the door to “super colonies” and shared territories.

This mutation is positively selected in the relatively open ecosystem of the US; however as Solenopsis populations continue to raise their numbers may reach a threshold that gives advantage to the more territorial variety (monogyny), this may push the species towards more geographic balance, as is evident in the South American native type.

I bring up Solenopsis because I just read a Science Daily article discussing how native lizards in the southeastern United States are adapting to potentially fatal invasive fire ant attacks by developing behaviors that enable them to escape from the ants, as well as by developing longer hind legs, which can increase the effectiveness of this behavior. This according to Penn State Assistant Professor Tracy Lang Penn, recently published in the journal Ecology

Here’s a nifty little video from Penn’s website showing a noosed lizard flicking away attacking Solenopsis - FYI the video skips for the first couple seconds:

Better the lizard than me! Solenopsis are aggressive, they like to lock on with their mandibles and sting multiple times – with painful and skin blistering alkaloid venom, Ouch!

Tracy Langkilde (2009). Fence Lizard Bulletin of the Ecological Society of America, 90 (1), 36-37 DOI: 10.1890/0012-9623-90.1.36

M. J. B. Krieger (2005). Molecular Evolutionary Analyses of the Odorant-Binding Protein Gene Gp-9 in Fire Ants and Other Solenopsis Species Molecular Biology and Evolution, 22 (10), 2090-2103 DOI: 10.1093/molbev/msi203


  1. Please forgive my ignorance about fire ants which we don't have in the UK (though some say we will get them - I don't understand how) but what do you destroy colonies in your yard? Can't you just spray them or powder them with insecticide? Or are they just too prolific that it's not worth doing? And do they ever, as some species over here do, turn into flying ants for a short period every year?

  2. Anthony:

    Fire ants (red variety) originally came to the US in the 1930’s as stowaways on cargo vessels; they made land fall along the Gulf Coast – probably at ports in Alabama. From there they spread like wildfire across the southeast. Although I’m not familiar with the UK’s situation in regards to Solenopsis, I’d venture to guess that they could cross the pond in a similar fashion.

    As you might guess, the trick to controlling them is to kill the queen (or queens) – which is no easy task; particularly given the rampant polygyny resulting from the Gp-9 mutation mentioned in the above blog. Although fire ants seem very tolerant of most insecticides designed for use around the house, some contact insecticides such as sprays and powders will work on the smaller mounds – if the queen isn’t too deeply burrowed. The queen(s) will even travel deeper into the mound if it’s disturbed, so digging out the nest before applying insecticide isn’t always a successful strategy either.

    I’ve personally had the best luck when using baited poisons that are collected and then carried to the queen by foraging workers. This however is a short term strategy, because the baited poison only remains affective within a meter or so of the treated mound, this leaves plenty of room for any surviving queens to retreat from the battleground and seed/join new nests elsewhere. Treating the entire yard with insecticide isn’t a great option either because it would be both expensive and risky to other wildlife. The expense of large scale insecticide treatments is one of the major issues facing farmers, ranchers and agriculturists. This is why many in the US have begun looking towards more natural and affordable biological solutions.

    One of the most promising biological control methods is the introduction of Solenopsis’ natural predators from South America - Phoridae.

    Phorid flies are known parasitoids of Solenopsis as well as a number of other ant species. The adult flies oviposit on foraging workers; their hatched maggots then travel into the ant's head capsule where they feed on muscle and nervous tissues. Within a week or two, this consumption leads to the decapitation of the ant.

    Decapitation is the dramatic end result of the fly’s work, but the biggest effect in regards to population control is the “fly avoidance behavior” exhibited by the Solenopsis. In the presence of the fly, workers will retreat into the mound to prevent oviposition. This avoidance behavior restricts the ability of the colony to forage and in turn weakens it to such extent that it readily becomes prey to rival native ants.

    Winged ants: Yes, both reproductive males and females grow wings, typically in the spring. Winged males will swarm together in response to certain pheromone signals by the female. She’ll then fly up and mate mid-air amongst the swarm. Following the romantic interlude, she’ll land, shed her wings and seed a new nest; the males die.

  3. Thankyou, fascinating reply. My god, they're much much worse than I feared, and winged ones too - help! I'm intrigued that a tiny little fly can conquer the mighty Solenopsis, but presumably they can, at best, only slow their spread. Then of course the introdction of "foreign" control species is hedged around by all kinds of problems - see, I think, the African land snail in Hawaii (and many other introduced species). Are there any viruses/fungi which can be used? And lastly, are their any benefits of fire ants?
    Damnit, it's really difficult to comment here - keeps coming back with an error message.

  4. AnthonyK,

    You’re absolutely correct – introduction of foreign species can be a roll of the dice. There are far too many variables to precisely predict what the long term consequences of such ecological alteration would be.

    As far as viral and fungal agents, I’m sure there are some out there – and I recall hearing that the University of Florida and the US Department of Agricultural were working on some pathogenic options a while back - but I really couldn’t speak knowledgeably about their current status or application. But you’ve certainly given me something to look into!

    Benefits: Solenopsis have tremendous appetites and feed on a variety of other arthropod species - many of which are agricultural pests. Although there may be situations in which a limited population of fire ants may be of benefit to a farmer’s crops, I’d be inclined to think that their bad outweighs their good. If at some point down the road a better ecological balance is reached through the natural selection of more territorial varieties, this may change, and Solenopsis may become less of a foe and more of a friend.

    If you continue to get an error when posting comments please take a screenshot or copy the message and email it to the address listed in my profile. I’ll see if there’s anything I can do from my end.


  5. Hi Johnny, et al,
    I fight fire ants in the Dallas Texas area, and have some hints for control from over here. First, the contact poisons do almost no good, besides being very harmful to the environs. The ants behavoir is to carry the queen away, down deep when they feel threatened, and they can smell the chemicals in acephtate(Ortho) and other mound treatments. Baits work pretty well, but you do not want to bait the mound. A ant mound is the colonies trash heap, they forage out a ways away from the mound. Baits, preferably with a slow acting poison, such as Spinosad(an organic stomach poison) work best. It takes very little bait to be effective. Ants do not actually eat the bait themselves, they feed it to their larva, which digest it into a liquid, which the mound then shares and drinks. The queen eats a lot so she gets it too. They thus have built in "tasters". Its important to bait all high importance areas, regardless of whether there are actually mounds present, as most fire-ant colonies are small pre-mound forming ones. This is an ongoing battle. You never actually win, just keep them at bay.

    I've have very good results with another organic method, with beneficial predatory nematodes. The nematodes only attack the soft bodied "grub" phase, but they do a pretty good job of reducing the populations. Nematodes seem to work best in shady moist areas, whereas baits work best applied in dry areas in the evening, as the ants are quit fussy about gathering old stale soggy bait. Any bait you buy and don't use at once should be sealed very well and stored cold and dry. The nematodes should be available at better garden centers or from Gulf Coast Biologicals.

    Fire ants do a lot of good, in turning the soil, they eat a lot of pests bugs, but also a lot of good bugs and other critters. They also farm aphids(and other sucking homopterians) for the honey, and can increase the problems with them. They seem to be increasing the problems on my Crapes with bark scale. I suspect that since fire ants are basically harvester type ants(grease and seed seeking) they probably eat a lot of weed seeds.

  6. chuckgoecke,

    Thanks for the info - I'm going to check into the nematodes. As you described above, a few days after applying baits I typically find small satellite mounds in the vicinity of the one poisoned – must be due to relocation of the queen.


  7. Hi,
    It makes me feel great when I read all these stories. It helps me from hopelessness and make me more stronger to fly… thank… for everything.