Formica subsericea (Silky Field Ant) Care Sheet

This guide was compiled and written by serafine of the 'Ants and Antkeeping' discord server, which can be found here. 

This guide has been posted with the permission of the authors. The original article may be found here:

I have edited this guide to make it more applicable to North American Formica-fusca group.

Caresheet - Formica fusca

Formica fusca-group is a group of large, black Formica species, many of which reside in North America including but not limited to F. podzolica, F. argentea, F. subsericea, F. accreta and F. glacialis. They can thus thrive in a broad variety of nests and nesting conditions.

In the wild, many species of the Formica-fusca group are regularly raided by Formica sanguinea-group ants and Polyergus (Slave-Maker Ants), Formica fusca-group ants are very forgiving - even if half a colony dies from flooding, escaping or a feral ant raid they will recover quickly.

Their relatively small colony size combined with their robustness and fast growth makes them a perfect beginner species, however they are also scared very easily and should be provided with a calm place that gets little to no vibrations. In addition, Formica demand a constant food source, and it is not unknown for queens to stop laying eggs for a period of months if their hunger is not satisfied.


-Familia: Formicidae/ants (Latreille, 1809)

--Subfamilia: Formicinae/scale ants (Lepeletier, 1836)

---Tribus: Formicii (Ashmead, 1905)

----Genus: Formica (Linnaeus, 1758)

-----Subgenus: Serrviformica (Forell, 1913)

------Species: Formica fusca (Linnaeus, 1758)

-------Subspecies: Formica fusca alpicola (Gredler, 1858), Formica fusca fusca (Linnaeus, 1758), Formica fusca fuscolemani (Samsinak, 1951), Formica fusca hyrcana (Arnol'di, 1968), Formica fusca maura (Santschi, 1929), Formica fusca tombeuri (Bondroit, 1917)

Basic information

Origin: North America, Europe, Asia

Habitat: prefers dry to mostly dry nesting spaces in open or partially shadowy landscapes, also often found in large parks and at the outer edges of city areas

Colony form: Usually monogynous, though polygynous populations are not uncommon within subsericiea, subaenescens, among other species

Colony size: usually 500-2000 workers with 1-15 queens (may grow to 5000 workers in captivity if fed well) 

Colony age: up to 25 years

Founding: claustral, pleometrosis and adoption

Workers: slightly polymorphic

Nesting sizes: soil nests under stones or in garden stone walls, sometimes also in dead wood.

Feeding: Trophobiosis, Zoophagy (liquid sugars und arthropods)

Hibernation: October – March at 5-10°C, hibernates with no brood (like all Formica species)

Reproduction: Nuptial flight from mid June to mid September, will swarm on humid warm days from noon to evening.


Workers: glossy black

Queen: glossy black

Males: glossy black


Workers: 4-8mm, varies by species

Queen: 12mm, varies by species

Males: 8mm, small head with big eyes, long abdomen

Development time

at 25°C

Workers: 4-6 weeks

Egg - Larva: ?

Larva - Pupa: ?

Pupa - Worker: ?

Antkeeping information

Recommended for beginners: Definitely yes, if you can keep yourself from disturbing them too much. The combination of fast growth, low aggressiveness and relatively small colony size makes it a perfect beginner species.

Temperature: Outworld: 18 - 30°C, Nesting area: 20 - 24°C

Humidity: Outworld: 30 - 50%, Nesting area: 50 - 60%

Nest types: Soil nest, sand-clay farm, gypsum, Ytong and 3D-printed nests (preferrably with a bottom coat of sand-clay or grout). The ants need moist areas for their brood, these can be provided by a water test tube attached to the nest.

Formicarium size: Should fit the current colony size.

Formicarium accessories: Optional heat source (heat mate, heating cable or heat lamp).

Substrate type: This species can walk well on most surfaces. Glass, vinyl tubing, acrylics, sand, clay and grout pose no issues. They can also climb vertical and upside down on glass.


Formica fusca shows very little aggression and instead does it's best to avoid conflict with other species, however big colonies can occupy aphid farms with a large group of workers and very aggressively defend them.

They are easily scared by vibrations and loud sounds (this includes playing loud music and slamming doors). In the wild they are often raided by other ants like Formica sanguinea and Polyergus rufescens against which they cannot defend, so they grab as much brood as they can and run out of the nest to make a new start somewhere else (or to return later when the raiders are gone). Since this is part of their natural behavior it's not that bad but it shouldn't happen too frequently. You should find a quiet spot for them far away from doors and loudspeakers, preferrably in a calm room (like not on your desk or in a hallway where a lot of people are walking by all the time).

Formica fusca workers use their superior speed to quickly maneuver through enemy territory looking for food sources of opportunity and even stealing food carried by other ants (in the wild they frequently steal from Lasius workers). They love to run around and while their colonies themselves don't require overly large nests they do need quite a bit of vinyl tubing and several outworlds to move around as they're meant to do. Outworlds should offer a grout or sand/clay bottom layer with some sand on top and a decent amount of decorations, so the ants can rush from cover to cover like the do in the wild.

Recruitment of nest mates is extremely quick and the workers will not hesitate to grab any food items they can find and quickly drag them back to the safety of their nest.

Additional antkeeping information

Formica fusca loves to run around. Workers forage alone or in small packs and can travel long distances while doing so. Their setup should pay tribute to this and offer wide open areas with long tubing parts in between them. Formica fusca workers are fine with sandy surfaces many other ants have problems traversing.

A water source should be available at all times but the nest itself can be kept rather dry (not bone dry though).

Formica fusca workers can walk very well on glass and due to their curious nature will always test out the escape barriers. Regular checks and barrier replacement is important, however due to their relatively small colony size and their jumpy nature this species is rather unproblematic even if a few workers should somehow manage to escape. You should definitely buy some spring steel tweezers to catch escaped workers without harming them, just in case (a transparent cup and a postcard might not be a bad idea either).

This species benefits enormously from a long and proper hibernation. Colonies that have hibernated well will outright explode into activity during the summer months.

Diet & Nutrition


Formica fusca will drink most sugary liquids, fluids are preferred over more viscous sugars.


Larger Formica fusca colonies consume a ton of insects. Their diet leans strong towards zoogphagy with sugars playing a lesser role. If you want a flourishing colony you will have to offer them insects, lots of insects. As soon as the colony has enough workers to care for the larvae they can raise an astonishing amount of brood in a very short time.

While the colony is hungry workers will immediately grab and drag everything towards the nest as fast as they can and as such any food items that can be carried by a single ant (or dragged by a small group of ants) are best suited for them. Flies and small crickets work very well but then Formica fusca aren't really picky when it comes to food. They are scavengers by nature and will avoid most living prey, unless it is tiny (like fruit flies).

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