Ant biology: April 2010 Archives

I live in the Northern USA and wanted to know if Fire Ants will ever be a pest in my yard?

The Red Imported Fire ant, Solenopsis invicta, is an introduced pest in the United States from South America. There are also native fire ants (species of the genus Solenopsis) found in many parts of the world, including the United States. Although the Red Imported Fire ant is an introduced pest in many parts of the United States, Australia, and some islands, it is unlikely you will ever have the invasive Red Imported Fire ant in the northern US since they are not able to survive long winters with hard freezes. Red Imported Fire ants are considered "hot climate specialists". This means they are unlikely to survive in your North Dakota yard, but may still be able to survive in places with temperature controlled environments like greenhouses. This species has even made the list of "100 of the World's Worst invaders":

Solenopsis invicta - Red Imported Fire ant. Photo by Alex Wild (

Where in the US are Red Imported Fire ants found?

The Red Imported Fire ant is thought to have been first introduced in the US in the late 1930's in the port of Mobile, Alabama. They are considered a serious problem due to many factors that include their ability to spread rather rapidly, their painful sting, aggressive behavior, and damage to some agricultural crops and livestock. In the United States fire ants have spread from Alabama across the southern US and into isolated areas of California, which has resulted in quarantines of movement of some products like soil and plants to help stop the spread of these invasive ants. Although we are not certain how much further north and west they will spread, we do know that they will not be able to survive outside in areas with long, cold winters.

Distribution of Red Imported Fire ants in USA. Map from:

Why are they called Fire ants?

Well if you have ever been stung by a Fire ant you can answer this question. Fire ants get their common name from the fact that when they sting you it feels as though you have been touched by a red-hot flame. These ants bite onto you (or other enemies, intruders or prey) with their jaws and then inject a dose of venom with the sting on the rear end of their body. Their sting is not only painful, but for some people this can be a real problem since it can result in anaphylactic shock or even death in very extreme cases. Also most people develop an itchy, puss filled bump after being stung.

Fire ant stings USDA.jpg

Fire ant stings. Photo from:

How can I identify a Fire ant?

Telling fire ants apart from other ants can be difficult since they look like most ordinary red/brown ants, although AntWeb and a microscope will help. Two of the key signs are their behavior (they are very aggressive and sting readily) and mound-shaped nests. Each of these mounds can contain up to 300,000 individual ants.

Fire ant mound AlexWild.jpg

Fire ant mound. Photo by Alex Wild (

Although this species is considered an invasive pest in some areas like the United States and Australia, it is important to keep in mind that they are not all bad. In their native range of South America it is one of many important ants in the ecosystem. For more information on the Red Imported Fire Ant, check out this webpage which contains many informative links:

- Corrie Moreau & the AntAsk Team

Ryan, this is a good question. The answer is not that easy though. Different ant species can have different numbers of queens in their colonies. In the majority of ant species, a single female establishes a new colony on their own (only one queen). When we talk about ant colonies that have one queen we use the term "monogyny" (mono = single; gyn = female/queen), and when talking about ants with multiple queens we use the term "polygyny". Polygyny occurs when young queens get together in groups of young founding queens (primary polygyny). Still others return to the nest they were born into and join their mother and sisters in this already established colony to also lay eggs (secondary polygyny).

Also, a single queen can mate with one or more males before starting her colony. There are quite a variety of different colony structures that have been discovered in ants ranging from the "standard system" of one singly-mated queen per colony to colonies with multiple queens or queens that mated multiple times. A good overview of different colony structures can be found in Heinze (2008). In analogy to the terms monogyny and polygyny we refer to mating once as "monoandry" (mono = single; andr = male/mate) and mating several times as "polyandry". The queens of army ants and leaf-cutter ants show extreme cases of polyandry and mating with 20 males is not unusual for these ant species. Monoandry is often common in ant species that have multiple queens. So there seems to be a trade-off between queen number and matings per queen.

Sometimes the only way to know how many queens a species has in the nest is to dig up the entire colony to count them. With over 14,000 ant species there are many that have never had their nests studied, so for many species we still do not know how many queens are in a nest or how many times she has mated.

Heinze J (2008) The demise of the standard ant (Hymenoptera: Formicidae). Myrmecological News 11:9-20

- Steffi Kautz & the AskAnt Team

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Good question Claude. As I am sure you know, ants, like most insects, don't do very well in the cold. But ants are always around in the spring when the weather warms up, so how are they surviving the winter? In general, the temperature underground is quite a bit higher than the air temperature. Ants take advantage of this by moving deeper underground in the winter. Some ant nests can be over 15 feet (4.57 meters) below ground level. They can also stay warm by grouping close together and sharing body heat.And ants in places where it is too cold to gather food during the winter may store food in their colonies and fill their crops (an extension of the gut used to store food and water) so that they do not starve.

So generally, ants hibernate during the winter, moving deep underground, grouping together, and generally limiting activity to conserve energy. Ants that live in particularly cold climates, like Leptothorax canadensis from Québec, Canada, and New England, USA, produce their own biological antifreeze so that the water in their bodies does not freeze. These ants are sometimes exposed to temperatures below -20° C (-4° F) but are able to survive even long cold winters by combining all of these methods for staying warm.

- Ben Rubin & the AntAsk Team

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