Off the Beaten Path

Cover Story: Annual Ant Control Issue - Cover Story: Annual Ant Control Issue

No matter the species, identification is important to know where ants might be, what they may be feeding on or foraging for, and how to treat. They may be small, but they are mighty!

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April 3, 2021

Whitney Cranshaw, Bugwood.org
Acromyrmex leaf-cutter ants foraging at night.

I have a confession to make. I hate ants. They are cool from a biological aspect; the sociality, the diverse adaptations and the sheer numbers. But I hate identifying them: they all look like ants. I can identify a fly off of a single wing, a cockroach from a leg and half the body, a beetle based on the head and antennae. Put a whole, intact ant in front of me and I start panicking. There are many species of common pest ants from fire ants to carpenter ants to white-footed ants. The NPMA Field Guide lists 19 common ants. That’s just a fraction of the number as there are currently 792 named species in the United States alone. While some are not as common, some are regional and some not as “pest-y,” they can still be important to identify so proper and effective treatment can be implemented. Here are a few of my favorites.

LEAF-CUTTING ANTS. There are three different species of leafcutting ants in the United States, mostly in the desert southwest and spanning into Louisiana. These ants, as the name suggests, cut pieces of leaves or other vegetation and take it back to their nests. They don’t eat the leaves, they use the leaves as a mulch to grow the fungus that they feed on. So these are essentially little farmers. Their nests can be quite large with millions of workers.

Because of what they are foraging for and eating, these are almost never an indoor issue. However, they can be extremely damaging to vegetation, especially with large colonies. Customers can lose vegetable gardens, ornamental shrubs and even small trees due to defoliation by the ants. While few insecticides are labeled for use on leaf-cutter ants, the mounds are easily identified by clearly trailing ants with leaves held above their heads and they are active during the day. Since they are foraging foliage and eating fungus, baits are ineffective for treating leaf-cutting ants. Often, the nearby vegetation can be treated to prevent ant damage.

These can be confused with harvester ants based on their appearance (spines on the thorax) but based on their behavior of leaf- carrying, that’s rarely the case.

Fun fact New queens must take a small bit of fungus from her old nest to start her new one in a different location.
Rover ant
Eli Sarnat, Antkey, USDA APHIS PPQ, Bugwood.org

ROVER ANTS. Five species of rover ants are present throughout the U.S. They are tiny ants that form nests in a variety of places, mostly small cavities in or just above the soil. If you are looking for a rover ant nest, focus on damp, mulched areas; they prefer high moisture and are more often found in mulch than other landscape areas. They do not bite or sting, but they are considered a nuisance ant. They can invade structures as they are foraging for foods and can potentially establish nests indoors. There hasn’t been a lot of research but we do know they feed on nectar and honeydew-producing insects, specifically subterranean aphids and scales feeding on plant roots. Eliminating that food source is a challenge! Since they are attracted to sweets, carbohydrate-rich baits can be effective. A study looking at different active ingredients showed imidacloprid as effective. However, they do not form clear trails so placing bait can be challenging. Eliminating above-ground food sources can help reduce populations and increase bait uptake.

Rover ants can be confused with the little black ant and odorous house ants.

Fun fact The dark rover ant is an invasive species from South America and was first discovered in 1978. It has spread from Louisiana to California and north through the southern states.
European red imported fire ant
Eli Sarnat, Antkey, USDA APHIS PPQ, Bugwood.org

MYRMICA SPECIES. Of the 70 species in this group, only one has a common name: the European fire ant. As the name suggests, these ants can sting and they are widespread and common especially in cooler climates of the United States. Like the Solenopsis fire ants, they nest in the ground, but without the characteristic obvious mounds. Also similar, they have lots of individuals and can have multiple queens, so eliminating the entire colony can be difficult. They are most often in areas of higher moisture so look for low areas and sprinkler or irrigation systems. These often will be found up against structures and around cluttered areas that hold heat from the day and keep the area slightly warmer at night. To help reduce populations, cultural controls like drying out the area and cleaning up yard clutter can help.

While you won’t confuse these with the red imported or native fire ants, they can be similar to field ants (Formica sp.) but field ants don’t sting and are rarely found in the high numbers that the Myrmica species will be found in.

Fun fact In areas where they are native (Europe and Asia), ants in this genus are considered important for the conservation of rare Phengaris sp. butterflies that trick the ants into carrying the caterpillars into their nests and caring for them until maturity.

KIDNAPPER ANTS. You may not think you have encountered kidnapper ants, but there are five species in the United States and they are fairly common. You likely have seen them, but thought they were a different species because of their behavior of kidnapping other ant species. A female queen enters an established nest of another species, kills their queen, and uses her new “subjects” to raise her brood and feed her new progeny. Kidnapper ant workers will raid other colonies, often field ant colonies, and kidnap the pupae and even late instar larvae. These ants will be raised by the original abducted ants and then get to the adult stage and help raise the colony themselves. So when you come across a field ant colony, there’s a chance it is actually a kidnapper ant colony. What makes these ants particularly interesting (aside from the fact they hijack other ant species!) is they are able to put off pheromones that make their victims less aggressive and more willing to accept their new ant overlords. Treatment of this species is taking out their workers, so treat them exactly as you would field ants.

These can be confused with field ants (though kidnapper ants are typically lighter brown).

Fun fact Kidnapper ants cannot survive on their own, even in laboratory colonies with ample food and resources, they still die out without additional labor.

ACORN ANTS. I saved my favorite for last. The around 50 species of acorn ants are so named because their colonies are “small enough to fit in an acorn.” That may seem like a stretch, but colonies have been found in old wood-boring beetle galleries, in galls and hollow plant stems. The colonies are typically around 100 to 200 workers, but there can be many colonies in a small area and there are often many satellite nests in close proximity. They are often arboreal and found in trees and other high places. In one sense, these are easy to treat because colonies are so small. On the other hand, there are often many individual colonies so if there is a “heavy” infestation, it can be challenging to get them all. That’s assuming you can find the acorns or other tiny areas they are inhabiting.

Acorn ants can be confused with little fire ants or acrobat ants, though acrobat ants have a more distinctive abdominal shape.

Fun fact One study looked at the starvation of colonies. They found most colonies survived over eight months of total starvation, though water was provided.

Chelle Hartzer is a Board Certified Entomologist at 360 Pest and Food Safety Consulting. Email her at chellehartzer360@gmail.com.