Solenopsis species: the Fire ants

MYRMICINAE

TRIBE: Solenopsidini

The Genus Solenopsis Westwood:
the Fire ants

Much of our general information about the genus is sourced from Wikipedia. 
There are more than 200 Solenopsis species around the world. Many species are known as ‘fire ants’, for two reasons: not only are most reddish-yellow in colour and occurring in large, vigorously biting swarms that reputedly resemble restless flames, they also have painful stings which cause a burning sensation and which they employ vigorously and without hesitation. However, not all are known as ‘fire ants’. Some are known as ginger ants, thief ants or merely red ants, but their habit of attacking in large numbers, with strong and painful stings, is pretty universal. 
The venom of fire ants (known as Solenopsin) is composed of alkaloids derived from piperidine. Some people are allergic to the venom, and as with many allergies, may experience anaphylaxis, which requires emergency treatment. Other problems are concentrated at the site of the sting. The sting swells into a bump, which can cause much pain and irritation, especially when several stings are in the same place. The bump often forms into a white pustule, which can become infected if scratched, but if left alone will usually flatten within a few days. The pustules are obtrusive and uncomfortable while active and, if they become infected, can cause scarring. Severe allergic reactions to fire ant stings, including severe chest pain, nausea, severe sweating, loss of breath, serious swelling, and slurred speech can be fatal if not treated.
Several Solenopsis species have become invasive in various countries. Solenopsis invicta, known in the United States as the red imported fire ant, is a serious pest in the USA, Australia, China and Taiwan, but fortunately has not yet been reported in South Africa. We do, however, have its invasive cousin, S. geminata [see below].
Most Solenopsis species have workers of several sizes, from small minors to much larger majors, but there are also workerless species that parasitize other ants, etc etc.


Solenopsis punctaticeps (Mayr, 1865)
Cape fire ant

First collected by Mayr in the Table Mountain forests [probably Newlands] in 1865, the species is widespread through sub-Saharan Africa, with several subspecies. The major workers have stings that are perfectly capable of penetrating human skin in softer areas, such as between toes and fingers. Some research suggests that some human individuals can have dangerous allergic reactions to Solenopsis stings (see above).



Solenopsis puntaticeps should not be confused with Solenopsis puncticeps, which does not occur in Africa. Why taxonomists should choose to give two such similar-looking ants such confusingly similar names is only something they can answer for, and hopefully one day they might have to.
The Cape fire ant comes in a range of sizes; the smallest minors are amongst the smallest of our ants and are indistinguishable with the naked eye from small yellow Monomorium ants. However, the smooth range of sizes from about 1.7 mm to about 3.7 mm distinguishes the species as a whole from any Monomoriums, Pheidoles or even Tetramoriums. The Monos and Tetras are always all the same size, whereas the Pheidoles only come in two sizes: normal and Extra Extra Large. What’s more, the XXL Pheidoles have very distinctive huge, square heads.
With a good mini-microscope fire ants can also always be told apart from other Myrmicine ants by the antennae, which consist of a shortish scape and only ten additional segments. The ‘club’ or tip of the antennae consists of only two segments, whereas in the Monomoriums with which they can be  easily-confused there are always three segments in the antennal club.
More technically, the clypeus of all Solenopsis species includes at least two, three or two pairs of prominent teeth. As the specific name of the Cape fire ant suggests, the head especially is pitted with distinctive ‘punctures’.
Most Solenopsis puntaticeps are a fairly consistent dull yellow ochre in colour, but the largest majors may have dark brown or reddish brown heads and even gasters. The Table Mountain ants are usually redder than our specimens, which are from the Grootvadersbosch biodiversity hotspot.
Our indigenous Solenopsis are all forest dwellers, nesting in rotting stumps and leaf litter. The colonies can be large, often numbering thousands of individuals. The queens are large [6.6 mm] and darker-coloured, and several may be present in the colony. The winged males are relatively large [5 mm] and black.

There are some good photos of this species at the following links, including one of winged alates [new queens] being launched on their nuptial flight:
www.ispotnature.org/node/555146
www.ispotnature.org/node/475889
www.ispotnature.org/node/568310

Arnold’s taxonomic description of Solenopsis punctaticeps is at 
http://antsofafrica.org/ant_species_2012/solenopsis/solenopsis_punctaticeps/solenopsis_punctaticeps_1_arnold1916.jpg

Survive invasive species:
Linepithema humile       : Argentine ants       : unknown
Pheidole megacephala  : House ants            : unknown
Lepisiota sp.                  : Small Black ants    : unknown
Technomyrmex albipes : White-footed ants  : unknown
Anoplolepis gracilipes   : Yellow Crazy ants  : unknown


Solenopsis geminata (Fabricius 1804)
Tropical fire ant
INVADER

The Tropical fire ant is an invasive ‘tramp’ species that has invaded tropical, sub-tropical and even some cool temperate regions around the world (they have been reported from Oxford, England). The ant is not only a problem because of its aggressive elimination of local small fauna and the agricultural damage it causes, but also because of its unpleasantly-aggressive behaviour towards humans. Some accounts claim that if you stand barefoot near a nest of these ants they will quietly swarm over your feet and then all sting you at once. We have not tested this unusual claim, but as this ant has been known as a pest since 1804 it’s not surprising that it has generated a few housewife’s tales. That said, its sting is powerful and may lead to dangerous allergic reactions in some people.



The ants are slightly larger than the Cape fire ant, ranging from about 2.2 mm to 5mm in length, and tend to be redder in colour, though in some parts of the world they are almost black. The colonies are very large and spread by ‘budding’. Antwiki quotes the entomologist  Creighton: 
“In general geminata prefers to nest in open fields or sunny glades, avoiding the shade of deep woods. The nests are usually irregular, sandy craters of loose construction but sometimes rotten stumps are utilized as nesting sites. The ferocity of this ant is proverbial, for the activity of the workers when disturbed never fails to attract attention, however callous the observer” (1930). 
S. geminata is also famous for its ability to form ‘rafts’ of ants, queens, and brood by linking legs together and ‘swimming’ across rivers or floodwaters to safety.
Although they are reputedly found in Cape Town in the Western Cape, we have not yet come across them here; our specimens are from East London, where we found them in 2010.

Creighton’s taxonomic description of Solenopsis geminata and its sub-species is at
http://antsofafrica.org/ant_species_2012/solenopsis/solenopsis_geminata/solenopsis_geminata_creighton1930b.pdf


Survive other invasive species:
Linepithema humile       : Argentine ants       : unknown
Pheidole megacephala  : House ants            : unknown
Lepisiota sp.                  : Small Black ants    : unknown
Technomyrmex albipes : White-footed ants  : unknown
Anoplolepis gracilipes   : Yellow Crazy ants  : unknown

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