Wasmannia auropunctata, known as the Little Fire Ant (LFA), was first detected on the island of Hawai‘i (the Big Island) in 1999. It is estimated that LFA has now spread to over 4,000 locations on the Big Island. LFA threatens native biodiversity, alters tropical ecosystems, impairs human health, impedes tourism, diminishes agricultural productivity, mars horticulture sales, and accordingly ranks among the world’s worst invasive species (Lowe et al. 2000).
LFA will sting endangered reptiles and birds, interfering with reproduction, nesting, and survival of young. LFA will sting cats and dogs in the eyes repeatedly over time and blind them (Theron 2005). Human stings are described as intense and painful with each encounter entailing a dozen or more stings. Human behaviors and habitats allow LFA to move quickly, disperse widely, grow to high densities, and inhabit locations not otherwise possible.
In Queensland, Australia, the government declared LFA invasions a “state of emergency” and took intensified actions in order to eradicate and stop the spread of LFA. There efforts have been much more successful then ours here in Hawaii. One main difference between Australian and Hawaiian LFA infestations is climate. Hawaii’s tropical climate is much more ideally suited for Little Fire Ant establishment and spread.
Arboreal (aerial nesting) - LFA can nest in an array of different locations but primarily like to be above ground, in a wet pocket of trees/plants/foliage. The three desired types of food come in the forms of sugar, protein, and oil. LFA are able to collect either one of these types of food by harvesting insects like aphids and mealy bugs, making these arboreal nesting ants completely self sustaining. Unlike in drier climates like in Australia where the ants must come down for food, LFA can live in trees forever. As of 2013, the Little Fire Ant has been recorded on four of the seven main populated islands of Hawai‘i: Kauai, Maui, Oahu and Big Island. Because of their mutualistic relationships Little Fire Ants prefer to nest close to where they can farm their food. Mealybugs, aphids and other tree insects are located above ground which in turn leads to LFA nesting in the air. LFA are arboreal creatures, they nest in trees. Sometimes those trees can be over 100 feet tall, and in some cases when food is short, or populations are extremely high they will be nesting that high above ground. This creates a great degree of difficulty to successfully control LFA infestations.
Polygyny (more than one queen per colony) - A typical ant colony consists of a single reproductive queen attended by many sterile worker ants. In a mature colony, new queens and males are produced at times when conditions for colony founding are optimal. The new queens and males fly from the nest in synchrony, mate while in flight, and the newly mated queens return to the ground, each attempting to form their own independent colony. The role of males ceases at this time and they do not return to the parental nest. However, nests of many invasive ant species (including Little Fire Ants) contain many queens, and workers do not appear to distinguish between them or attempt to assassinate surplus queens. This feature gives the species two competitive advantages. First, with most ants the founding phase of a new colony carries a high risk of failure. A newly mated queen needs to lay an initial clutch of eggs and care for them until the larvae reach adulthood, before focusing exclusively on egg-laying. New queens often suffer from predation or fail to raise sufficient workers to form a colony. For Little Fire Ants and many other invasive ant species however, newly mated queens simply re-enter the parental colony, or move a short distance with existing workers to found a new satellite colony that remains in contact with the parental one The second advantage of polygyny is that the task of egg laying is shared between multiple queens. In single queen colonies, the death of the queen results in the end of the colony however this is not true with LFA.
Polydomy and unicoloniality (multiple nest sites which are inter-connected) - Ant colonies, even from the same species, are highly competitive and expend great resources to defend their territory and resources from other colonies. Large amounts of energy may be expended in this activity. Almost all invasive ants share the traits of polydomy and unicoloniality which dramatically reduces their cost maintaining territory. Individual Little Fire Ant colonies do not compete with each other. Instead they form an inter-connected network of nodes or buds. They work cooperatively, share food, workers, brood and queens and jointly defend their combined foraging areas against competing ant species. Territorial defense is only needed at the outer edges rather than around each individual colony and the ratio between border length and foraging area reduced substantially. The surplus energy resulting from this strategy is re-allocated to colony expansion and is one key to their invasive ability..
Density - Introduced Little Fire Ant populations can achieve extraordinary population densities far greater than the species they displace. In Hawai`i’s tropical orchards, LFA populations average 20,000 individuals per square meter (Souza et al. 2008). Queen density is also high. Using empirical data for worker to queen ratios elsewhere (Ulloa-Chacon and Cherix 1990) queen density in Hawai‘i are estimated to be between 36 and 77 per square meter. This level of queen redundancy confounds efforts to control the species. At one time Dr. Cas estimated that on an average 1/4 acre house lot there can be as many as 20 million worker ants and 40,000 queens. Each queen can lay hundreds of eggs a day.