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Formica subsericea, commonly known as Silky Field Ants, are medium-sized and fast-moving ants often found in forests, grassy areas, and suburban neighborhoods. These ants are part of the Formica fusca complex and can be confused with similar species such as Formica argentea, F. podzolica, and F. glacialis.


Silky Field Ants are relatively easy to care for, despite being fast and somewhat anxious. They can recover from significant worker or brood losses, as they are often targeted by slave-making ants such as Polyergus mexicanus and Formica sanguinea-group ants. As long as the remaining workers can adequately feed the queen and brood, the colony can quickly rebound. However, queens may stop laying eggs if the food supply is insufficient.


This species can become easily stressed by noise, vibrations, and intense light, which might lead the queen to eat her eggs. Therefore, it's best to keep them in a quiet and undisturbed environment.


Silky Field Ants are omnivorous, feeding on liquid sugars, insects, and other arthropods. They typically build nests against trees, under rocks, or in logs, and are commonly found in the eastern United States and Canada.


Colonies are usually monogynous but can sometimes be polygynous, growing up to 2000 workers, and in captivity, they might expand even more if well-fed. These ants are known for their resilience, often recovering quickly even if half the colony is lost to external factors.


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Formica Subsericea (Field Ants)

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  • Scientific name: Formica subsericea


    Geographical distribution: All throughout Canada and USA.

    Queen size: 7-10mm


    Male size: 4-8mm, varies per species


    Worker size: 8mm


    Natural habitat: As the name suggests, the Silky Field Ants usually nest in open or shadowy grasslands and plains while also being able to nest in dead wood. They are usually seen in city edges or in neighborhoods with chunks of vegetation and forests for the Formicas to get food and nest.

    Circadian activity: Formica subsericea is mostly diurnal so their activities are performed during sun hours.


    Mating flight period: The Silky Field Ants fly anywhere from mid June to early September. They will have multiple flights, after a significant rain at around 12-5PM, instead of having one or two big flights. 


    Queen founding method + ¿polygynous or monogynous? : Formica subsericea is olygynous, meaning they start with multiple queens but then they usually end up killing each other once workers arrive, meaning they are mostly monogynous. Some species of the fusca complex may be able to have polygynous colonies but unless you have the specific identification for you queens, the multiple queen foundation will end with a massacre between the queens until one remains or the workers will choose the most dominant queen and kill the rest.


    These fusca group species are all fully claustral so they do not need any food to raise the first generation of workers. They can also be boosted with other colonies' brood if the growth of the queens foundation isn't doing well.


    Average growth rate:

    Egg to larvae: 6-15 days

    Larvae to pupae: 7-21 days

    Pupae to worker: 5-14 days

    The average growth rate of this species in the first brood batch is of 5-6 weeks (at a stable temperature of 26 °C/78.8 °F)


    Average colony size: The Silky Field Ants colonies can get to a couple thousand individuals, over 5000 in polygynous species but in captivity, it's usually colonies of around 500-1500 workers but they can get to the higher thousands of well fed.


    Nesting preferences: The usual subsericea will like nests on the dry side, ~50-65% of RH (relative humidity), inside the nest. They will also prefer soil nest, sand-clay farm, gypsum or Ytong with a moist area for the brood and queen. Giving them sand and other substrate can be very useful for the ant's survival as the Silky Field Ants are anxious ants and they like to build their own nests so if you give them 3D nests and ytong/other similar material nests, it's better to give substrate. An additional note is that the subsericea ant likes vertical nests.


    Recommended temperature: A temperature of 22°C to 27°C is more than enough for a stable and healthy colony growth but their sweet pint is probably 25-26°C/76-78°F, while the outworld can be several degrees higher than the nest temperature.


    Recommended humidity: As it's been already mentioned, the nesting humidity should be of around 50% to 65% of RH even though the moist area for brood and egg development should be a little higher. The outworld should be at around 25-50% of RH or up to 60% of humidity for the short term. It should be noted that the whole setup should be well ventilated to prevent any fungus growth that could be harmful for the ants.

    Food preferences: These ants eat most sugars, like honey and sugar water and small fruit pieces, they aren't picky for that. Now, these ants are very fast and aren't aggressive, they don't like living prey for proteins. Formica subsericea is mostly a scavenger species and it will often adventure into other colonies' territories to rob food the other ants have found, they avoid any type of confrontation with other ants. The Silky Field Ants are mostly protein consumers so they need good quantities of insects which can go from grasshopper legs to fruit flies and small roaming prey like baby roaches and crickets.

    Feeding schedule: When it comes to these Field Ants, proteins should be prioritized, so for small colonies of 5-25 workers, feeding them proteins 2-3 times a week with small protein quantities, such as 5-10 hydei fruit flies or 1-2 baby crickets/half a mealworm. Carbohydrates like honey water/sugar water should be fed 1-2 times a week. As the colony grows, the amount of food should augment and once the colony is a couple dozen workers big, close to a hundred, you can feed them more often, if you want their growth to stay fast. Larger colonies' (50+ individuals) workers (including the queen) will look pretty skinny and will try to escape when they are hungry. In extreme cases, they'll eat their brood!


    Hibernation (Diapause) details: Subsericea ants' nests usually stay at -5°C or above. It is recommended to stay above freezing point in captivity as we cannot easily duplicate the slow cool down into freezing temperatures. Hibernation is recommended between 39F (4°C) - 50F (10°C). The Silky Field Ants hibernate with no brood so don't get stressed if you see little to no eggs/larvae while they are in hibernation. You should check the colony monthly while they are in dormancy and feed them if necessary (carbohydrates only).


    Escape barrier: Fluon, petroleum jelly, oils and talcum powder + isopropyl alcohol methods work fine. Apply a barrier along the top edges in a circular motion covering several centimetres.

    Difficulty rating: The Silky Field Ants are a rather easy species to care for as they have not so big colonies compared to other ants and they are not very aggressive either. One bad thing about them is that they always need water and food or they will stress and start eating their brood and the queen can stop the egg production for several weeks/months and they really like nests with soil so they require a little bit of special care but they aren't good at escaping so I think these speedy ants can get a 8/10.

    Bite/Sting rate: Formica subsericea has a powerful bite but it only hurts when multiple ants do it and they also produce Formic acid so receiving a large quantity of it can be painful as well.

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