Solenopsis molesta
From Antweb.org
From Antweb.org
Introduction
Solenopsis molesta is a tiny species from the subfamily Myrmicinae and Tribe Solenopsidini. These ants earned the nickname 'thief ants' due to their tendency to sneak into other species' nests and steal their food and brood. Their miniscule size makes them difficult to detect, and even if the victims manage to detect their presence, they are still incredibly hard to target and grab onto.
Range
A highly successful species, S. molesta is found across the majority of North America. Its northern range includes the Canada's southern provinces that border the U.S. Its southern range extends far into northern and central Mexico. The species is present on the Atlantic, Pacific, and Gulf coasts, as well as the center of the continent and the entirety of the United States.
Worker Size and Coloration
Workers are between 1.2 mm and 1.3 mm in length according to AntWiki. Queens are between 4 mm and 5.5 mm. Workers are monomorphic, and do not have a major subcaste. Color varies from dark brown to bright yellow, although the majority of specimens are typically orange, yellow, or in between.
Taxonomy and Relation to Fire Ants
Solenopsis molesta are related to fire ants. The genus Solenopsis can be split into two groups: fire ants and thief ants. Fire ants include species groups such as the S. geminata group (which has S. geminata, S. xyloni, the parasitic S. aurea, etc.) and the S. saevissima group (which has S. invicta, S. richteri, etc.). They are typically medium sized and several mm in length, much larger than S. molesta. Thief ants are a part of the S. molesta species complex, which besides S. molesta includes Solenopsis texana, Solenopsis krockowi, Solenopsis carolinensis, Solenopsis validiuscula, etc. All thief ants are around 1 mm - 1.5 mm in length and behave similarly if not identically to S. molesta. The S. molesta complex does not possess stingers capable of penetrating human skin, unlike fire ants.
Made by Aaron567
Solenopsis molesta as a species is understudied, and many speculate that it is actually multiple species within the S. molesta species complex, separated by geographic range.
Diet and as an Agricultural Pest
Solenopsis molesta is a major agricultural pest. It is primarily granivorous, feasting on seeds. These ants enjoy corn kernels, which is a problem for farmers who plant corn in the ground. They not only destroy newly planted corn seed but also damage corn cobs. They enjoy other varieties of seeds as well, though are still omnivorous and will readily accept insects as supplemental protein.
Brood Development Time
Brood development occurs rapidly due to their small size, taking 3-4 weeks if properly heated.
Nuptial Flight Details
Nuptial flights occur in August and September. In South Dakota, Solenopsis molesta flights typically coincide with Lasius neoniger and Lasius brevicornis flights, and their main flights typically occur in late August - early September. Small flights have been observed as early as July and as late as October. These flights occur in the late evening around dusk, beginning around 7:00 PM CST, again coinciding with Lasius flights. In their main flight on August 18, 2025, queens began falling to the ground after mating around 7:30 PM, and dealate queens can be found in large numbers well into the night. Stragglers can be found the following morning. The high for the day was around 30 degrees C or 86 degrees F. It rained roughly 8 mm or 0.3 inches the previous night, and wind speed was 6 - 10 kph, or 4 - 6 mph with gusts never exceeding 16 kph or 10 mph. The conditions were sunny and humid. Solenopsis molesta flights are not conspicuous due to their small size, though the flights of Lasius neoniger, whose flights typically coincide with S. molesta, are quite conspicuous. Workers will swarm their nest entrances making them wider, and eventually (for mature colonies) hundreds of queens and thousands of males will be released. This is a good indicator that S. molesta are also flying. Dealate queens were found in 'pockets'. Certain areas of pavement had dozens of queens congregating and trailing towards their parent nest or a new nesting site. Other areas, predominantly those with established colonies of other species, were devoid of dealates.
Polygyny and Nest Inbreeding
Many populations of Solenopsis molesta, primarily east of the Rocky Mountains, are highly polygynous. Formiculture user Mdrogun from Illinois (at the time) documented his captive colony's alates breeding in the nest, turning his 5 queens into 15 queens. He caught multiple mating pairs in the act on camera:
Roughly 4 weeks later, that number quickly rose to 40 wingless queens:
Both videos by Mdrogun
In South Dakota, queen number varies. Some smaller colonies only have 1 queen, though I have observed multiple wild colonies with hundreds of queens. From my observations and experiments, it appears the local populations will readily accept new queens into the nest. It is a logical assumption that besides nuptial flights, this population of this species reproduces by budding as well.
Most populations on the west coast (most likely candidate to be a different species) are monogynous.
Resources
Journals
Solenopsis molesta Journal - Ant Keeping Journals - Ants & Myrmecology Forum
Ender Ants' Solenopsis cf. molesta Journal - Ant Keeping Journals - Ants & Myrmecology Forum
Articles
Solenopsis molesta species complex - AntWiki
The Thief Ants, Solenopsis molesta Group, of Florida (Hymenoptera: Formicidae) on JSTOR
A Preliminary Report on the Life-Economy of Solenopsis molesta, Say.
Solenopsis molesta (Thief Ant) Care Sheet – Canada Ant Colony
ADW: Solenopsis molesta: INFORMATION
Thief Ant - PennState Extension
Thief Ant, Solenopsis molesta - Urban and Structural Entomology Program at Texas A&M University
Solenopsis molesta - Mississippi State University (Say)
Solenopsis molesta – OhioAnts
Southwestern Thief Ant (Solenopsis krockowi) | Stateside Ants
Pergande's Thief Ant (Solenopsis pergandei) | Stateside Ants
Update 1
August 28, 2025
On the night of August 18, 2025, Solenopsis molesta, Lasius neoniger, and Lasius brevicornis had their main nuptial flight. Ants_Dakota and I collected hundreds of Lasius brevicornis and Solenopsis molesta queens near Dunham Park in a suburban environment in Sioux Falls. See more details of the flight in the 'Nuptial Flight Details' segment of this post.
Seeing as colonies in the area can naturally accumulate hundreds of queens, I am attempting to create a self-propagating supercolony of these ants with hundreds of queens and tens of thousands of workers. As the colony produces alates, they will breed in the nest and their queens' numbers will grow. I chose a high number of queens to start with for their high nanitic count and to bring as much genetic diversity as possible to mitigate the effects of inbreeding.
As of today, August 28, the queens laid a gargantuan mountain of an egg pile, easily 10x the mass of a single queen. It has several hundred if not close to 1,000 eggs. Only 4 queens have died thus far, which for such a large group of queens is a tremendously high success rate. They are in a 20mm test tube, and despite their numbers their size allows them to fit comfortably in the same test tube. They only fill half of the test tube including their egg pile, and the queens prefer to pile on top of each other instead of spreading themselves out.
I have noticed that large groups of slow-moving queens tend to behave like a liquid. If you move around the test tube (don't try this once they've laid eggs), the queens will take the shape of their container, can be poured, and can flow. The large number of queens means very few of them have a good grip on the walls, and instead grip each other, making them behave in this way. I have developed a set of laws to explain this phenomenon:
Assume the following:
Queen Liquidity = Q
Number of Queens = n
Average Queen Velocity = v
Group of Queens' Surface-Area-To-Volume Ratio = A
Queen Grip Strength = g
Queen Stress = x
Queen Viscosity = s
Queen Movement = m
How Seriously You Take This = c
Your Stupidity = lmao
RushmoreAnts' Laws of Queen Liquidity:
1st Law
As average queen velocity decreases, liquidity increases.
Q = -nv
2nd Law
As a group of queens' surface-area-to-volume ratio decreases, the number of queens able to grip a surface decreases. As the number of queens able to grip a surface decreases, liquidity increases.
A = ng and Q = -ng.
Therefore,
Q = -nA.
3rd Law
Queen stress is directly proportional to queen liquidity. As queen stress increases, queen movement increases. As queen movement increases, queen viscosity increases. As queen viscosity increases, queen liquidity decreases.
m = nx, v = nm, and Q = -nm.
Therefore,
Q = -nx.
4th Law
lmao = kc
In the wild these ants are mostly cryptic, hiding behind leaflitter and parasitizing other ant colonies. In captivity, they are much more aggressive and love being out in the open. I look forward to their first batch of several hundred nanitics.
Edited by RushmoreAnts, Yesterday, 9:10 PM.
