Introduction

Red Imported Fire Ants, Solenopsis invicta (入侵紅火蟻) , which were recently reported locally belong to the genus of insects called Solenopsis (火蟻屬) and are in the family Formicidae (蟻科). The ant was first reported from South America and spread to other parts of America, Australia and China. At least 266 species of the genus have been reported from various countries. Compared with the only species, Solenopsis geminata (火蟻 / 熱帶火蟻) , previously found locally, Red Imported Fire Ants are more aggressive and attack anything that disturbs their mounds (nests) or food source. Unlike honey bees, red fire ants can sting repeatedly. However, they will not transmit diseases through their stings.

Identification of Red Imported Fire Ants

The Red Imported Fire Ants can be distinguished from other ants by some characteristics. These ants are of medium size ranging from 3 to 6 mm in length (which are about the same size as those ants commonly found indoors). They have a 2-segmented pedicel (waist) and a sting at the end of the abdomen. Their bodies are usually red to brown in colour, with a darker abdomen. They possess a pair of compound eyes and 10-segment antennae with the last 2 segments form a segmented club. The ant has three projecting structures (so called "teeth") coming out from the clypeus, which is the front part of the head, and four projecting structures ("teeth") at the edges of the mandibles (upper jaw).

Biology of Red Imported Fire Ants

Red Imported Fire ants undergo complete metamorphosis which includes 4 stages: eggs, larvae, pupae and adults. These adults include winged, black-bodied males, red-brown winged females, one or more queens and wingless workers. Their colonies are individually established by newly mated queens following a mating flight.

The ants build their nests in form of mounds in almost any type of soil, but prefer open, sunny areas or partially shaded ones. The mounds may be built under logs, rocks or other materials lying on the ground. They usually have no obvious entry hole. They are, on average, 250 mm to 610 mm in diameter and 450 mm high. But larger mounds are not uncommon. The mounds are dome-shaped in appearance and served with tunnels which can be up to 10 m long. The mounds could be 2 m deep inside the ground. As the ants are attracted by electricity, their nests may be found in buildings and equipment around electricity systems.

Importance of Red Imported Fire Ants

1. Human health :

Red Imported Fire Ants can bite and sting the victim repeatedly. Venom injected by these ants cause an itching and burning sensation (hence the name "fire ant") followed by the formation of a white pustule to form in 1 to 2 days. These pustules are prone to secondary infection if broken and may leave permanent scar. A few people are hypersensitive to the venom and may develop chest pains or nausea, or lapse into a coma or very rarely even death.

2. Agricultural impacts :

Red Imported Fire Ants also cause economic losses by feeding on agricultural crops. They are a serious seed feeders and attack sunflowers, okra, cucumbers, soybeans, corn and eggplant. They also damage irrigation systems and their mounds disrupt harvesting operations. They cause the death of livestock such as calves, small pigs and domestic animals.

3. Economic impacts :

Red Imported Fire Ants' colonies can infest electrical equipment such as air conditioners, traffic signal boxes, electrical and utility units. Telephone junctions, airport landing lights, electric pumps for oil and water wells, computers, and even car electrical systems have been reported to be affected in many countries. The ants chew on the insulation or carry soil into these areas and cause short circuits.

Prevention and control of Red Imported Fire Ants

Inspection

1) inspect the premises particularly the shady areas of earthen floors, areas near to electricity system and water pipes, electrical boxes, switch rooms for electricity and telephone as well as machine rooms regularly to ensure the places are clean and tidy;
2) inspect ornamental plants regularly;
3) saturate the soil of potted plant in a container with hot water until water comes out from the hole at the base of the pot for expelling ants nested in the soil, if any;

Insecticide application

4) spray the exterior surface of plant pots with residual insecticide to prevent the ants from moving in to or out from the pots;
5) apply knock-down insecticide (such as domestic pesticide for the control of flies ) for getting instant killing effect on foraging fire ants indoors;
6) apply insecticide with slow killing effect, such as those baits for controlling ants and cockroaches for elimination of the ants;
7) apply a chemical barrier using residual insecticide (such as domestic pesticide for the control of cockroaches ) on frames of doors and window openings to outdoors for protection to prevent ants from entering the premises;
8) apply insecticide with knock-down effect directly to surrounding and then the centre of the mound of the ant until the liquid of the insecticide comes out from the mound for the destruction of the mound; and 9) apply insecticide in water base if the application is on plant or soil directly.

Personal protection

1) avoid direct contact with these ants;
2) avoid entering scrubby areas;
3) wear protective clothing, such as shoes or boots and/or tuck pant legs into socks during outdoor activities;
4) avoid handling soil and vegetation/plants with bare hands;
5) apply talc powder to the handles of space, plough, and other gardening tools to prevent ants from climbing on to the tools; and
6) For severe reaction following a suspected red fire ant sting, seek medical advice.

Employing private pest control company

Consider appointing a pest control company for providing professional services on Red Imported Fire Ants control and prevention. (How to select a pest control company)

Pest Control Advisory Section