This species is believed to be native to Central America. It has been spread world-wide by human commerce and is now abundant in most tropical areas around the world. It is a close relative of the well-known common fire ant Solenopsis invicta. It does not however have the same invasive tendencies and is more restricted in its range and ability to colonize areas out of its particular environmental niche. It is classified as a 'hot climate specialist' as it resides only within warm tropical regions and habitats in other climates are unsuitable for its successful colonization.
Even in Thailand which is classed as a warm tropical country this species has only colonized areas which are open and exposed. Due to the seasonal monsoonal weather, they are unable to successfully establish colonies in areas that are too moist or heavily shaded - and are not found in undisturbed natural forest habitats.
They are unable to colonize areas in countries where temperatures regularly fall below 10 degrees centigrade for any significant length of time. At these lower temperatures the colonies become inactive and cease foraging - and as they are not programmed for hibernation and do not have any method of long-term food storage the colonies will slowly die out.
In low temperatures the colonies become inactive but they can survive several days of low temperatures without any adverse effects on the colony. This ability has helped them spread to other countries where they are inadvertently transported by ship / plane amongst commercial products such as plants etc.
The workers are an attractive red-orange coloration and are 2-3 mm in length. There is also a major form which has a larger head and is 3-5 mm in size.
Normally colonies only have a single queen which is notably larger than the workers at about 8 mm; occasionally large established colonies will accept a second or third queen. Queens are reputed to live up to 7 years and when their egg laying ability starts to fall off or she dies the workers will replace the original queen with a new one accepted into the nest after flights.
All castes are equipped with a strong sting which they will use at the slightest provocation.
New colonies are established by fertile queens following a mating flight. Colony budding also occurs in large colonies, resulting in the outwards radiation of a colony and these supplementary sub colonies will also often accept newly fertilized queens.
Unlike many species that have a seasonal swarming period this species will produce alates for several months of the year and in Thailand they can be found flying continually from late May to the end of November.
The winged reproductive male and females leave the nests on nuptial flights near dusk on days following rain, during the warmer periods of the year. The males are quite large and mating occurs on nearby shrubs or on the ground.
The mated queens then have two options and will either attempt to enter an established colony or dig a burrow to start a new colony.
The majority of newly mated queens seek moist areas within a few kilometers of the parent colony to start their own nest. Once a suitable site is found the female sheds her wings and constructs a small sealed chamber at a depth of about 5 cm. On some occasions two or three queens will dig a chamber together and aid each other to raise the first workers. However; once a small number of workers have emerged (20-50) the workers themselves will kill the weaker queens leaving only one.
A large number of mated queens frequently flood areas where this species has colonies, but most fail to produce new colonies, however those who strike lucky will form new colonies very quick.
The new queens begin laying eggs within 48 hours and will they will lay around 10 to 15 eggs each day for up to 10 days, after which she will stop laying eggs until the first workers are mature in about four weeks. The first workers are typical minims being much smaller than normal workers.
The initial speed of the brood's development is very important for these new queens and most don’t manage to establish colonies as the site chosen to establish a colony is not ideal. Environmental factors can slow down the brood's development resulting in most newly mated queens failing to raise their first workers before their food reserves are depleted. It is only the queens that are in prime open localities that have a good chance of establishing a new colony.
Fire ants are ground nesting ants. They prefer to construct nests in southerly exposed, raised dry banks which benefit from the warming action of the sun. This species generally builds nests in stony sandy soil in open, sunny areas. Contrary to reports this species does not construct large mounds as such, just slightly raised domes of soil from their deeper excavations.
They prefer to forage under covered trails and in underground tunnels which extend from the nest in all directions and they forage both during the day and night. This species prefers low to mid-elevations and is not found in highland areas. Peak foraging activity is reported to occur between a temperature range of 25 to 32°C. Above or below this and their foraging activity is greatly reduced.
The colonies will frequently move to new locations migrating over 30 meters from the original nest. These migrations are probably stimulated due to a change of habitat such as growth of shade producing plants or exhaustion of the local food supply.
S. geminata show very aggressive territorial interactions, and eliminate many other ant species during their growth in an area. They are more aggressive than most native species and hence have pushed many other ant species away from their local habitat.
Once successfully established colonies can become quite large with between 15-20,000 workers and in ideal conditions colonies will bud outwards. This species is also noted for its ability of being able to raise a large amount of brood per worker ratio, and under good conditions colonies will have a massive brood and increase in size very quickly.
They vigorously defend their nest and when disturbed they have a 'swarm reaction' pouring out of the nest in large numbers to attack any intruder. This action can be illustrated in captivity by lightly blowing on the entrance of the nest. The reaction is immediate and large numbers of ants will swarm out of the nest ready to attack!
They are opportunistic foragers and will take a wide range of foods. S. geminata is omnivorous, but at times of the year when other food is not available it is known more as a seed-feeding species. They also tend honeydew producing insects and feed on a wide range of dead or live insects.
They possess a venomous sting that gives them the ability to subdue relatively large invertebrate prey, and even small vertebrates. It prefers food with high protein content but will feed on almost anything, including many human foods rich in carbohydrates or fats.
In the past this species seems to have been frequently confused with the invasive fire ant Solenopsis invicta. There are however several notable differences between these species:
S. invicta usually forms multi queen colonies that can have anywhere from 10-100 individual queens, while S. geminata usually has only 1–3 queens per colony.
S. invicta constructs distinct mounds of soil and the colony size is very large often in the region of 50-200,000 ants. S. geminata does not produce a noticeable mound and the colonies are much smaller with only about 15-20,000 ants.
S. invicta is well known for its very painful sting, the effects of which last a long time and can leave painful blisters. S. geminata also has a painful sting but the effect is over quick and usually does not leave any painful swelling. I have been stung many times by this species and in my opinion the effect of the sting can be likened in intensity to the sting of the Common Red Ant of Europe - Myrmica rubra.
S. invicta is also much more adaptable and able to invade a wide range of habitats while S. geminata is less adaptive and limited in its habitat colonization ability.
Apart from microscopic differences an easy way to identify the different species is that S. invicta has a wide range of worker sizes, but they are all the same form with heads that are the same width as, or narrower than their abdomen. In S. geminata there is a distinct major form which have heads that are distinctively wider than their abdomen.
It is important to obtain fertilized queens, as some suppliers collect and sell all the queens they can capture, and there is a high chance that some will be infertile.
We collect our queens after they have been attracted to a night light in the early evening. They are then left overnight, and in the morning, we only select only the queens that have removed their wings - those still with wings are released back into the wild.
Queens can raise colonies individually or in small groups of 2 or 3. However, although the group queens will have a larger brood - as soon as about 20-30 workers have emerged, they will kill all but one queen.
Hobbyists who are not experienced will often fail in raising a colony from just a queen as they are quite particular regards environmental conditions, and greatly dislike any form of disturbance during the foundation stage. To be sure of success in establishing a colony, you should purchase a young queen with at least 30-50 workers.