Red Imported Fire Ant
\nThe
Red Imported Fire Ant (
Solenopsis invicta), or simply
fire ant, is one of the 266
species of
ant in the widespread
genus Solenopsis. Although the Red Imported Fire Ant is native to
South America, it is best known in the
United States and
Australia. Colonies were accidentally introduced to the USA in the 1930s (probably via ship to
Mobile, Alabama) and to Australia in
2001.
Fire ants are more aggressive than most native ant species and have a painful sting. A person typically encounters fire ants by accidentally stepping into one of their mounds, which causes the ants to swarm up the person's legs, attacking
en masse. The ants respond to pheremones that are released by the first ant to attack. The ants then swarm and immediately sting when any movement is sensed.
Fire ants are efficient competitors to other ants, and have been successful at enlarging their range, notably in the U.S., where they have gradually spread north and west despite intense efforts to stop them. Today they are found in most of the southern states, including
Texas. It is not uncommon for several fire ant mounds to appear suddenly in a suburban yard or a farmer's field, seemingly overnight.
(At least one community uses the presence of fire ants as a publicity opportunity:
Marshall, Texas, hosts an annual
fire ant festival.)
Fire ants are still on the move, too, often traveling from one area to another in turf, root balls of nursery plants, and other agricultural products. They are a pest not only because of the physical pain they can inflict, but also because their mound-building activity can damage plant roots and lead to loss of crops. Although their stings are rarely life-threatening to humans and other large animals, they can kill smaller animals such as birds. They sometimes kill newborn calves, if the calves do not get on their feet quickly enough.
At present fire ants in the US can be controlled but not eradicated. One of the main problems with RIFA is that they cannot be killed by conventional methods such as flooding. If the ants sense a change in water levels in their nests, they will come together and form a huge ball that is able to float on the water, with the workers on the outside and the queen inside. Once the ball hits a tree or other stationary object, the ants swarm onto it and wait for the water levels to recede. A number of products are available which can be used on a mound-by-mound basis to destroy ant colonies when they appear. With all such efforts, it is important to reach and kill the queen (or queens), which may be as far as six feet underground; otherwise the queen may simply move a short distance away and quickly establish a new colony.
During reproduction, the sexual male workers sprout wings as do the queens. The sexual males and females then fly into the air, sometimes as high as 100 ft, in a large cloud. Once a male finds a female, it latches onto the female and drops to the ground. After injecting the female with sperm, the male dies.
Since the introduction of the RIFA, it has become a major agricultural and urban pest throughout the southeastern United States. In addition, fire ants cause both medical and environmental harm.
An outbreak of the ants in
Queensland occurred in 2001. It is believed the ants were present in shipping containers. Only after sustained government inaction became a major public issue did substantial control measures begin to be put into place. A five year AU$145m eradication programme has begun involving the employment of 500 controllers and the baiting of 100,000 homes. The first of 12 chemical treatment rounds in the
Brisbane area was 80 percent successful according to Queensland Primary Industries Minister Henry Palaszczuk.
Body structure
\n
Fire ants are symmetrical along the body, meaning that the left part is the mirror image to the right. The ants have hardened exoskeleton, meaning that they have no bones or internal supporting tissues, but tough integuments for support and protection. The fire ants breathe through their tracheas.
Their bodies can be classified into three major parts: head, chest and abdomen. They have three pairs of legs, and a pair of antennae attaching to the head. (personal interview) Just like other ants, the worker and soldiers ants are female. The queen is responsible for laying thousands of eggs. The number of males is low, because only one male is needed for the entire reproduction.
Unlike most people’s perception that fire ants bite and inject venoms, they actually have stings like most wasps and bees do. The stings are located at the end of their abdomens. When the fire ants sting, they use their strong mandibles to attach themselves to the victim’s flesh, and then they can sting for many times continuously.
Life cycle
The life cycle starts with the queen mates with a male. After mating, the male dies, and the female begins to lay eggs. During the process, the queen has to survive on her previously deposited food and her shed wings as energy source. The queen would first lay about ten eggs that would also take ten days to hatch. It will be approximately twenty more days before the larvae become worker ants. As a result, the first worker ants are very small in size. Gradually, the size and the number of worker increase as the queen is fed with more nutrients.
Spread
\n\n
A Queen red fire ant captured from a neighborhood in
Houston,
Texas. The ant was placed in a
computer scanner and scanned. Its body was slightly crushed during the scanning.
Countermeasures
Red Imported Fire Ants have virtually no natural enemies in the United States or Australia. Many scientists and agencies are attempting to develop methods to stop the spread of fire ants.
The prevention of plague has been through pesticide use, but current research is introducing natural enemies of the Red Imported Fire Ant — microsporidian protozoan Thelohania solenopsae and the fungus Beauveria bassiana are promising pathogens. Pseudacteon tricuspis and Pseudacteon curvatus — parasitoid flies from South America — decapitate worker ants in the final stages of larval development. Solenopsis daguerri (Santschi), a parasitic ant, invades RIFA colonies to replace the queen in hopes of gaining control of the colony. For this reason, it is also being probed as a biological control agent.
Some work is being done in the area of biological controls. One promising avenue involves introducing a species of phorid fly found in the ants' native habitat that parasitizes the ants. A fascinating description of the parasitization mechanism may be found at this external site: [1] Large-scale use of such controls is not likeley in the short to medium term, however. Past experience demonstrates that hastily adopted biological control agents can do more harm than good (the Mosquitofish in Australia is an example), and it remains to be seen how much success biological control of the Red Imported Fire Ant will have.
See also
External link
\n*Official Queensland site
