Argentine Ants 

Scientific Name: Iridomyrmex humilis (Mayr)
CLASS/ORDER/FAMILY: Insecta/Hymenoptera/Formicidae
METAMORPHOSIS:Complete

Introduction:

This species, which is native to Argentina and Brazil, was probably introduced at New Orleans via coffee ships from Brazil before 1891. Argentine ants are found in the southern states and in California, with isolated infestations in Illinois, Maryland, Missouri, Oregon, and Washington.

Identification:

1/4" (4-6 mm) in length. Body varies from light to dark brown. Antenna 12-segmented, without a club. Thorax lacks spines, profile unevenly rounded. Pedicel 1-segmented. Gaster with anal opening slitlike, lacking circlet of hairs. Stinger absent but can bite on provocation. Workers emit a stale greasy or musty odor when crushed..

Similar Groups:

1. Odorous house ant (Tapinoma sessile) has pedicel/node nearly hidden by front edge of abdomen/gaster, emit a sweetish rotten coconut odor when crushed.
2. Crazy ant (Paratrechina longicornis) with legs very long in relation to body size, antenna! scape (1st segment) at least 2 times head length, anal opening circular, surrounded by circlet of hairs.
3. Other small dark ants with 2 nodes/segments in pedicel and/or thorax with 1 or more spines/teeth on
upper surface.

Biology And Behavior:

Colonies are located in moist situations near a food source. They include a few hundred to several thousand workers and many queens; numbers fluctuate seasonally. In the autumn, outside colonies join together to form huge overwintering nests. Development time (egg to adult) is 33-141 days, averaging 74 days. Winged female reproductives are rarely seen because mating takes place inside the nest. The workers are very aggressive and usually eliminate other ant species and some other insects from the area. However, ants from different Argentine ant colonies are friendly and do not fight.

All Argentine ants are the same size. They travel with well-defined trails between their web of nests and their food sources. Argentine ants feed on sweets, honeydew and oily household foods.

Argentine ant queens are different and unusual when compared to queens of other ant species. Some of those dissimilarities and behavioral characteristics are:

1. Argentine ant queens are small, about 1/6 – 1/4 inches in length, much smaller than most other species of
ant queens

2. Winged Argentine ant queens mate once with a winged male, after which they can continuously produce fertile eggs for as long as they live. While other ant species have seasonal swarming flights, these ants do not form new nests through mating swarms. Instead, they mate inside the nest.

3. A single Argentine ant colony will have several queens, each of them capable of laying as many as 60 eggs
per day.

4. Argentine ant queens help workers by feeding their young. Most other ant queens primarily lay eggs and depend on the ant workers to feed and care for the young.

5. Argentine ant queens are mobile and may be seen outside the nest along with workers, unlike other ant queens who reside inside the nest for life. Queen mobility enables the rapid movement and establishment of nests to other areas if conditions become inhospitable.

6. At times, due to temperature or colony pressures, an Argentine ant queen will leave her nest without taking flight and establish a new nest.

Reproduction and mating within Argentine ant colonies is quite different than other ant species. Winged queens mate once with a winged male, after which the queen can continuously produce fertile eggs for as long as 10 years or until her death. Unlike most other ants, several productive queens can share the same colony. When colonies become too crowded, one or more queens will leave with some workers to form a new colony in another location (a process called budding). Budding usually occurs in the spring and summer.

Habits

Inside, these ants usually nest near a moisture source such as water pipes, sinks, potted plants, etc. The workers follow regular trails when foraging, and winged queens can sometimes be found among trailing workers. Workers commonly tend honeydew-producing insects. The preferred foods are sweets such as sugars and syrup but they will feed on almost every kind of food including meats, eggs, oil, fats, etc.

Outside, Argentine ants typically live in shallow nests located in moist situations such as under boards and stones, beneath plants, along sidewalks, etc. This ant prefers sweets such as honeydew' fruit juices, and plant secretions, but also steals seeds, attacks poultry chicks, disrupts bee hives, etc. Their habit of crawling over everything including refuse, sewage, sputum, carrion, etc. affords them the opportunity to transport the causative disease organisms for dysentery, etc.

Control

Location of the nest(s) and its treatment with a residual insecticide is ideal; try following ants back from the food source. Be sure to pull back the grass from around foundation walls and the edges of concrete sidewalks and driveways because these ants will trail below the grassline where they are not visible. Baiting and use of boric acid dust in the voids of the outside ground-floor walls is the preferred treatment. Outside perimeter barrier treatments are essential and must be well maintained.