Red Imported Fire Ants

Scientific name: Solenopsis invicta

How to identify red imported fire ants

Red Imported Fire Ants (Solenopsis invicta) are coppery brown in colour. Nests will show a mix of sizes being 2-6mm in length. Workers measure between 2.4 and 6.0 mm. Queens have a head length of 1.27 to 1.29 mm and a width of 1.32 to 1.33 mm. Eggs are tiny and oval-shaped, remaining the same size for around a week. After one week, the egg assumes the shape of an embryo and forms as a larva when the egg shell is removed. Larvae measure 3 mm

Where are red imported fire ants commonly found?

Red Imported Fire Ants thrive in urban areas, especially in backyards, golf courses, parks, recreational areas, school grounds, and street verges. In residential areas, look for the loose mounds of dirt with no obvious entry or exit holes in and around, lawns, footpath edges, garden beds, near taps and utility pits. On rural properties, they can be found around dams, along the edges of cultivated land, crop land post-harvest, along fence lines, in and around piles of organic matter.

Why are red imported fire ants considered a pest?

Red Imported Fire Ants are known to have a strong, painful, and persistent irritating sting that often leaves a pustule on the skin. An animal, including humans, typically encounters them by inadvertently stepping into one of their mounds, which causes the ants to swarm up the legs, attacking en masse. The ants respond to pheromones released by the first ant to attack and sting in concert, often killing smaller animals by overloading their immune systems.

Fire ants are excellent natural predators and are biological controls for pests such as the sugarcane borer, the rice stink bug, the striped earwig, aphids, the boll weevil, the soybean looper, the cotton leaf worm, the hornfly, and many other pests harmful to crops. However, they also kill beneficial pollinators, such as ground-nesting bee species. Seeds, fruits, leaves, roots, bark, nectar, sap, fungi, and carrion are all fire ant prey, and they are not shy about creating their own carrion, either. They are proficient enough at overwhelming intruders that they can virtually clear an area of invertebrates, lizards, and ground-dwelling birds.

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, lead to loss of crops, and interfere with mechanical cultivation. It is not uncommon for several fire ant mounds to appear suddenly in a suburban yard or a farmer's field, seemingly overnight. Their stings are rarely life-threatening to humans and other large animals, causing only 80 documented deaths as of 2006. However, they often kill smaller animals, such as birds. They sometimes kill newborn calves if they do not get on their feet quickly enough. The sting of the RIFA has venom composed of a necrotizing alkaloid, which causes both pain and the formation of white pustules that appear one day after the sting.

They represent a seious threat to health, environment and economy, causing painful bites to people, pet and livestock. The venom can cause a wide variety of symptoms in humans from pustule sores, to eczema to anaphylactic shock.

What is the biology and lifecycle of red imported fire ants?

Studies have been conducted on the sex ratios exhibited within colonies of RIFAs. More specifically, it was observed that the queen actually predicts the sex ratios. In an experiment, 24 field colonies were selected with highly biased sex ratios in a monogyne population. Eleven of these colonies were male specialists, and 13 were female specialists exchanging queens, twenty-two of the 24 colonies accepted the foreign queen, and 21 of these colonies produced a new batch of reproductive 5 weeks later.

It has been observed that RIFAs workers not only tend to queens indiscriminately, but they also indiscriminately attack them. After temporary cooperation associations end between queens, a queen who produced more workers gained no advantage over the less productive queens. Queens producing diploid males reared fewer offspring but were as likely to survive as queens producing only workers. It would have been assumed that if workers controlled queen mortality, they would be expected to discriminate in favour of their mother, therefore increasing their inclusive fitness.

Management Tips For Red Imported Fire Ants

The key to fire ant control is to locate all mounds and treat them and then prevent their reoccurrence.

Mounds can be treated by drenching with liquid insecticides or by baits containing Fipronil. Fipronil is carried by back to the ant mounds by the workers and then fed to the ant population. Fipronil is then spread throughout the colony by means of food sharing by the worker ants. This slowly wipes out the entire population including the queens.

Fipronil is non-repellent to the ants, which means that they cannot sense that there is a pesticide, or toxicant present, which greatly encourages feeding and the consumption of the bait. An outdoor perimeter application of a liquid insecticide helps to prevent their entry into homes.