Grouping Kentucky Ants
By Their Number of Petiole Nodes
07/26/2024 – by pest expert Matthew S. Hess
Grouping ants based on the number of petiole nodes present between the thorax and the gaster is one step in helping distinguish one species from another. By making this grouping and memorizing which ants belong to which group, it becomes much easier to recognize each species.
As hexapod invertebrates, ants belong to the class Insecta, the order Hymenoptera, and the family Formicidae. Insects are the largest group within the arthropod phylum and Hymenopterans are the third largest group of insects. The order Hymenoptera also include bees, wasps, sawflies, ichneumons, and gall wasps. This order completes metamorphosis and is divided into two groups: Apocrita, which have a narrow waist (like ants and wasps) and Symphyta, which have no waist. Ants are further classified into one of 17 living subfamilies that belong to one of three clades (descendants of a common ancestor): formicoid, leptanilloid, and poneroid. The subfamily is used as the first step in identifying ants by classification. There are 21 subfamilies of ants worldwide. Of those 21, there remain 17 living taxa and four found only in fossil records. Myrmicinae are the largest species, followed by Formicinae.
Ants are classified as follows:
- Domain: Eukaryota
- Kingdom: Animalia
- Phylum: Arthropoda
- Subphylum: Uniramia
- Subphylum: Hexapoda
- Class: Insecta
- Order: Hymenoptera
- Family: Formicidae
- Genus: over 300 genera world-wide
- Species: over 15,700 named species and subspecies
Understanding Where the Petiole Nodes are Located
Here, the primary anatomical features of an ant can be seen.
Thorax
The thorax of ants comes after the head and before the petiole. This are will either have an even or uneven profile. All six legs attach to the thorax by way of the apodeme. The apodeme forms a joint with the basal segment of the leg called the coxa.
Petiole
When distinguishing between ants and termites, a key feature to look for is the difference in waist shape. Ants have a pinched waist, while termites have a broader waist. This distinction is caused by the petiole. The petiole is the constricted area of the gaster that connects it to the thorax, resulting in the unique “pinched” waist of ants. This area is flexible, allowing ants to move the gaster for various reasons.
Nodes
Depending on the species, ants may have one or two nodes on the petiole. The nodes are upright, angular structures affixed to the superior portion of the petiole. To properly identify the number of nodes, a magnifying glass or jeweler’s loupe may be necessary. Identifying the number of nodes helps in identification purposes.
Here, the petiole and nodes can be clearly seen
Gaster
The ant’s gaster is the abdomen, which contains the heart, defense chemicals and venom, and the digestive system. The gaster may be used in defense or against prey. The petiole nodes are in front of and connected to the gaster.
Ant Species with One Petiole Node
- Black Carpenter Ants
- Red Carpenter Ants
- Field Ants
- Large Yellow Ants
- Odorous House Ants
- Small (False) Honey Ants
Black Carpenter Ants (Camponotus pennsylvanicus)
The Black Carpenter Ant is polymorphic, meaning there are several different sizes of ants within the colony as small as 1/4 inch to as large as 1/2 inch (and sometimes a bit larger). These can range in color from black to red. The thorax has an evenly rounded profile and only one node is present on the petiole. At the tip of the abdomen there is present an acidopore (a round orifice circled by hairs). Carpenter ants can induce a painful bite.
- Subfamily: Formicinae
- Tribe: Camponotini
- Genus: Camponotus
- Species: Camponotus pennsylvanicus
- Caste Phenotype: Polymorphic
- Size: 1/4 to 1/2 inch in length (queens are 3/4 of an inch long)
- Color: Black to red
- Thorax: Evenly rounded profile
- Petiole Nodes: 1
- Acidopore: Present
- Sting: Absent
- Bite: Yes
- Ocelli: Absent
- Threshold:
- At sight of 1 or two indoors, action should be taken to eliminate
- Best Management Practices
- Remove nests if located indoors (vacuum and destroy contents)
- reduce moisture indoors
- Keep landscape clean and free of debris and moisture
- Maintain 16″ distance between plants and structure
- Eliminate limbs hanging over structure
- Treatment Methods
- Direct nest treatment with proper insecticides
- Bait designed for carpenter ants
- Other identifying or unusual characteristics
- Carpenter ants destroy, but do not eat wood
- Largest of Kentucky’s native ant species
Red Carpenter Ants (Camponotus sayi)
Like the Black Carpenter Ant, the Red Carpenter Ant is also polymorphic. However, sizes are smaller and range from about 1/4 to 3/8 inch for major workers and 3/16 inch for minor workers. The thorax is evenly rounded from a side-view. Only one petiole node is present. A circle of hairs is present at the tip of the abdomen.
- Subfamily: Formicinae
- Tribe: Camponotini
- Genus: Camponotus
- Species: Camponotus sayi
- Caste Phenotype: Polymorphic
- Size: 3/16 to 3/8 inch in length
- Color: Red with black gaster
- Thorax: Evenly rounded profile
- Petiole Nodes: 1
- Acidopore: Present
- Sting: Absent
- Bite: Yes
- Ocelli: Absent
- Threshold:
- At sight of 1 or two indoors, action should be taken to eliminate
- Best Management Practices
- Remove nests if located indoors (vacuum and destroy contents)
- reduce moisture indoors
- Keep landscape clean and free of debris and moisture
- Maintain 16″ distance between plants and structure
- Eliminate limbs hanging over structure
- Treatment Methods
- Direct nest treatment with proper insecticides
- Bait designed for carpenter ants
- Other identifying or unusual characteristics
- Carpenter ants destroy, but do not eat wood
Field Ants (Formica spp.)
Field ants are about 3/8 of an inch long and have variable colorations including tan, brown, red, black, or red and black. This species is often confused with carpenter ants. Unlike other species, this ant worker has ocelli (simple eyes) on the front of their head above and between the compound eyes. The thorax is uneven. There is one petiole node. At the tip of the abdomen there is present a circle of hairs.
- Subfamily: Formicinae
- Tribe: Formicini
- Genus: Formica
- Species: Formica spp.
- Caste Phenotype: Monomorphic
- Size: 3/8 inch long
- Color: Tan, brown, red, black, red and black
- Thorax: Uneven profile
- Petiole Nodes: 1
- Acidopore: Present
- Sting: Absent
- Bite: Yes
- Ocelli: Present
- Threshold:
- In Turf: a few scattered mounds should be acceptable
- In Sports Fields: A few mounds could begin reducing the turf’s
- Best Management Practices:
- Inspect for and reduce potential nesting sites
- Treatment Methods
- Sprinkle ant bait granules around mounds as per label instructions
- Other identifying or unusual characteristics or behaviors:
- Often confused with carpenter ants
- Mounds, although much different, could be confused with Fire Ant mounds
Small (False) Honey Ants (Prenolepis imparis)
Also known as the Winter Honey Ant, this species has a triangular abdomen when viewed from above. They are a shiny yellow-brown to dark brown. This abdomen enlarges as the ant feeds (similar to a tick or a bed bug) and becomes greatly enlarged when the gaster is full of food. This species measure around 1/8 of an inch in length. Their thorax is uneven when viewed from the side and almost appears pinched when viewed from above. The first segment of their antenna is longer than the head. They have a one-node pedicel that appears heart-shaped when viewed at an angle. There is a circle of hairs at the tip of the abdomen.
- Subfamily: Formicinae
- Tribe: Lasiini
- Genus: Prenolepis
- Species: Prenolepis imparis
- Caste Phenotype: Monomorphic
- Size: 1/8 inch in long
- Color: Shiny yellow-brown to dark brown
- Thorax: Uneven profile
- Petiole Nodes: 1
- Acidopore: Present
- Sting: Absent
- Bite: Yes
- Ocelli: Present
- Threshold:
- Best Management Practices:
- Reduce or eliminate insects that provide protein or honeydew
- Removal of objects or debris on soil that provide harborage
- Treatment Methods:
- Direct colony injection in cracks and crevices or ground nests
- Direct treatment to foraging ants
- Sweet baits
- Other identifying or unusual characteristics or behaviors:
- Viewed from an angle, the pedicel and node appear heart-shaped
- Abdomen appears triangular when viewed from above
- Abdomen may be engorged on workers
- Thorax appears pinched when viewed from above
- First antennal segment longer than head
- Colonies are small, often less than 1000 workers
Large Yellow Ants (Acanthomyops interjectus)
Also known as the Citronella ant. These are about 1/4 inch long. Ironically, they range in color from yellow to yellow-orange, reddish-yellow, or light brown. When crushed, these ants give off an odor reminiscent of citronella. The eyes are small compared to their size. The thorax is unevenly shaped. At the tip of the abdomen, there is a circle of hairs.
- Subfamily: Formicinae
- Tribe: Lasiini
- Genus: Lasius
- Species: Acanthomyops interjectus
- Caste Phenotype: Monomorphic
- Size: 1/4 long
- Color: Yellow, yellow-orange, reddish-yellow, and light brown
- Thorax: Uneven profile
- Petiole Nodes: 1
- Acidopore: Present
- Sting: Absent
- Bite: No
- Ocelli: Present
- Threshold: Nuisance only
- Best Management Practices:
- Reduce potential nesting sites
- Treatment Methods:
- Usually no treatment necessary indoors
- Outdoors, mound drenching can be performed
- Other Identifying or unusual characteristics or behaviors:
- Smell like citronella when crushed
- Compound eyes are small
- May swarm indoors (through cracks or crevices) but rarely nest their
Odorous House Ants (Tapinoma sessile)
The odorous house ant is one of the most common ants found indoors, especially in kitchens, and is dark brown to black in color. They measure about 1/8 of an inch long. When crushed, this species gives off a rotten coconut-like odor. The thorax is uneven in shape but not as predominately as other species. The pedicel has one node that is hidden by the abdomen, which is pushed forward toward the thorax. There is no circle of hairs at the tip of the abdomen.
- Subfamily: Dolichoderinae
- Tribe: Dolichoderini
- Genus: Tapinoma
- Species: Tapinoma sessile
- Caste Phenotype: Monomorphic
- Size: 1/8 inch long
- Color: Dark brown to black
- Thorax: Mildly uneven profile
- Petiole Nodes: 1
- Acidopore: Absent
- Sting: Absent
- Bite: Rarely
- Ocelli: Yes
- Threshold:
- Best Management Practices:
- Repair/seal cracks, crevices, and holes in foundations, windows, doors, walls, and other potential entry areas
- Reduce nesting materials
- Eliminate food sources
- Treatment Methods:
- Control foraging ants with sweet, fast-acting baits
- Control the colony with sweet, slow-acting baits
- Other Identifying or unusual characteristics or behaviors:
- Most common species found indoors
- Smell like rotten coconut when crushed
- Will nest in old termite-damaged wood
- Maintain large colonies with satellite colonies
Ant Species with Two Petiole Nodes
- Acrobat Ants
- Big-Headed Ants
- Little Black Ants
- Pavement Ants
- Pharaoh Ants
- Thief Ants
- Black Imported Fire Ants
Acrobat Ant (Crematogaster lineolate)
At just barely longer than 1/8 of an inch, he Acrobat Ant derives its name from their habit of holding the abdomen (gaster) above their thorax when disturbed (similar to a scorpion lifting it’s tail forward). On the uneven thorax there is a single pair of spines. Unlike other species whose pedicel connects to the front of the gaster, Acrobat ants have a two-node pedicel that connects to the top of the gaster, giving the appearance that the gaster is upside down. When viewed from above, the gaster resembles the shape of a heart. This species has a shiny body and can be brown, black, light red, or a combination of these colors, including multicolored.
- Subfamily: Myrmicinae
- Tribe: Crematogastrini
- Genus: Crematogaster
- Species: Crematogaster lineolate
- Caste Phenotype: Monomorphic
- Size: Slightly longer than 1/8 inch
- Color: Black, brown, light red, a combination of those colors, or multicolored
- Thorax: Uneven with a pair of spines
- Petiole Nodes: 2
- Acidopore: Present
- Sting: Present
- Bite: Yes
- Other Identifying or unusual characteristics or behaviors:
- Abdomen is heart-shaped when viewed from above
- Abdomen can be lifted above the thorax
- Petiole connects to top of abdomen
- Abdomen appears to be upside down (compared to other ant species)
Big-Headed Ant (Pheidole spp. [In KY, Phediole dentata and Phediole magacephala])
The invasive Big-headed ants have two sizes of workers. The major workers have a very large head and are about 1/8 inch long while the minor workers have a much more proportional head and are about 1/16 inch long. They are typically dark reddish-brown but can be found yellow or ginger in appearance. The first segment of their antenna is short and they have an uneven thorax with one pair of spines and a two-node petiole. Big-headed ants also construct mud tubes similar to termites.
- Subfamily: Myrmicinae
- Tribe: Attini
- Genus: Pheidole
- Species: Pheidole spp.
- Caste Phenotype: Polymorphic
- Size: 1/16 to 1/8 inch long
- Color: Dark reddish-brown (sometimes yellow/ginger in appearance)
- Thorax: uneven with a pair of spines
- Petiole Nodes: 2
- Acidopore: Absent
- Sting: Absent
- Bite: Yes
- Other identifying or unusual characteristics or behaviors:
- Some workers have very large head
- Construct termite-like mud tubes
- Invasive and may compete against other species
Little Black Ant (Monomorium minimum)
The little black ant is monomorphic and about 1/16 of an inch long. Their shiny coat ranges in uniform color from dark brown to jet-black. Besides their color, they are similar in appearance to the Pharaoh Ant. They have a 12-segmented antenna with a 3-segmented club. The uneven thorax has no spines present and the petiole has two nodes.
- Subfamily: Myrmicinae
- Tribe: Solenosdini
- Genus: Monomorium
- Species: Monomorium minimum
- Caste Phenotype: Monomorphic
- Size: 1/16 long
- Color: Dark brown to jet-black
- Thorax: Uneven
- Petiole Nodes: 2
- Acidopore: Present
- Sting: Present (very small)
- Bite: Yes
- Threshold: Difficult to control. Any sighting of activity should prompt action.
- Best Management Practices:
- Keep cracks and gaps in foundations, walls, windows, and vents sealed.
- Remove plant mulch and debris from foundation.
- Reduce moisture indoors.
- Remove food sources and keep food in containers.
- Treatment Methods:
- Remove nests with vacuum (also vacuum up some cornstarch with the nest) and destroy contents afterwards. Use approved baiting methods.
- Other identifying or unusual characteristics:
- Besides their color, they resemble Pharaoh Ants
Pavement Ant (Tetramorium caespitum)
In KY, the pavement ant is the only ant whose head is covered in visible grooves. Additionally, their thorax contains striations. They are about 1/8 inch long and monomorphic. They range in color from reddish-brown to dark brown or black with a specifically shiny abdomen, and have lighter colored legs and antenna. Their abdomen ends with a sting.
- Subfamily: Myrmicinae
- Tribe: Solenosdini
- Genus: Tetramorium
- Species: Monomorium minimum
- Caste Phenotype: Monomorphic
- Size: 1/8 inch long
- Color: reddish-brown to dark brown or black with a shiny abdomen
- Thorax: Slightly uneven with pair of spines
- Petiole Nodes: 2
- Acidopore: Absent
- Sting: Present
- Bite: No
- Threshold: One or more ants should prompt control action, especially where grease and food debris are present.
- Best Management Practices:
- Keep food areas clean.
- Sweep and mop floors regularly, removing food debris from becoming embedded in corners and under baseboards.
- Seal cracks, holes, and gaps in foundation walls, windows, doors, etc.
- Store foods in pest-proof containers.
- Treatment Methods:
- Remove grease and food debris.
- Place foods in pest-proof containers
- Use baits (sometimes up to several applications to achieve control)
- Other identifying or unusual characteristics:
- Head and thorax are covered in striations.
- Abdomen is shiny.
- Legs and antenna are lighter in color than body
Pharaoh Ant (Monomorium pharaonis)
This species may be easily confused with the Thief Ant except for their 3-segmented antennal club rather than the 2-segmented antennal club of the Thief Ant. Like the Theif Ant, the Pharaoh ant’s antenna has 10 segments. They range in color from yellowish or light brown to a slight reddish color with their abdomens often noticeably darker. However, their bodies are almost transparent, making them difficult to see. They have no spines on the thorax and a 2-node petiole. Pharaoh ants have a harmless sting present and an acidopore at the rear of the abdomen. Pharaoh ants are of particular importance in medical or medical related facilities because of their small size, almost transparent bodies, and preference for warm, dark, and humid areas indoors. They are known to carry and transmit dozens of bacteria, diseases and pathogens to people and pets.
- Subfamily: Myrmicinae
- Tribe: Solenosdini
- Genus: Monomorium
- Species: Monomorium pharaonis
- Caste Phenotype: Monomorphic
- Size: 1/16 inch long
- Color: Yellowish or light brown to a slight reddish
- Thorax: Uneven
- Petiole Nodes: 2
- Acidopore: Present
- Sting: Present
- Bite: Yes
- Threshold: Any activity should prompt immediate action. Pharaoh Ants have been known to vector food-borne diseases and other illnesses and diseases not food-borne.
- Best Management Practices:
- Use IPM to reduce numbers.
- Reduce food sources inside building.
- Reduce nesting materials
- Treatment Methods:
- Do NOT apply repellant liquid or aerosol pesticides (colonies can easily bud)
- Do NOT make applications directly to nesting sites
- IGRs have been found to effectively stop reproduction of workers
- Use only baits that work well for both grease and sweet ants
- Other identifying or unusual characteristics:
- Known to transmit diseases
- Commonly infest hospitals and similar facilities
- Bodies are almost transparent
Thief Ant (Solenopsis molesta)
Also known as the Grease Ant. This species is often confused with the Pharaoh Ant. However, it is smaller, at only 1/32 to 1/20 of an inch, has much smaller eyes, has only a two segmented club on the antenna, and has a sting. Like the Pharaoh, the Thief Ant has ten antennal segments, no spines on the thorax, and two nodes on the petiole. They range in color from yellow to bronze and dark brown. Thief ants commonly nest near other species and raid them for their food cache, eggs, and larvae.
- Subfamily: Myrmicinae
- Tribe: Solenosdini
- Genus: Solenopsis
- Species: Solenopsis molesta
- Caste Phenotype: Monomorphic
- Size: 1/32 – 1/20 inch long
- Color: Yellow to bronze or dark brown
- Thorax: Uneven profile
- Petiole Nodes: 2
- Acidopore: Present
- Sting: Present (very small)
- Bite: Yes
- Threshold: Any activity should prompt action.
- Best Management Practices:
- Clean up garbage, pet foods, and other foods
- Seal entryways and other cracks and crevices
- Remove nests when found
- Treatment Methods:
- Use slow-acting baits designed for protein or grease ants.
- Other identifying or unusual characteristics:
- Often confused with the Pharaoh Ant
- Has tiny eyes
Black Imported Fire Ant (Solenopsis richteri)
Often referred to as BIFA, this invasive species can be easily distinguished from all other North American species by their 10-segmented antennae with a 2-segmented club. Along with these dissimilarities, the BIFA also has a sting. This polymorphic species has several sizes of workers present in the colony ranging from 1/32 of an inch up to 1/4, and are reddish-brown to black with a darker abdomen and sometimes have a large, reddish-orange or yellowish spot on the first segment of the gaster. Fire ants are extremely aggressive and both bite and sting. The thorax is uneven and there are two nodes on the petiole. These construct large mounds, usually no more than 18 inches tall and a few feet in diameter. What’s different about these mounds than other ant mounds is that they have no visible openings.
- Subfamily: Myrmicinae
- Tribe: Solenosdini
- Genus: Solenopsis
- Species: Solenopsis richteri
- Caste Phenotype: Polymorphic
- Size: 1/32 – 1/4 inch long
- Color: Reddish brown to black with darker abdomen
- Thorax: Uneven profile
- Petiole Nodes: 2
- Acidopore: Absent
- Sting: Present (painful)
- Bite: Yes
- Threshold: Any activity should prompt action directed at control. Fire ants can be extremely dangerous, especially to small children and the inferm.
- Best Management Practices:
- Control while in landscape, before entry into buildings
- Do not disturb mounds (ants may bud and start multiple colonies)
- Avoid receiving dirt, rock, or mulch from areas known to be infested
- Treatment Methods:
- Use slow-acting baits applied near mounds
- Do not disturb mounds.
- Only apply liquid insecticides by full-mound drench
- Other identifying or unusual characteristics:
- 10-segmented antenna with 2-segmented club
- No opening on their mounds
- Mounds may reach 24 inches tall and 24 or more inches in diameter
- Will swarm immediately upon mound disturbance
- Bites and stings are painful
- Attack in large numbers and are very dangerous
