How to Care for Formica subsericea | The Silky Field Ant Guide
Updated: 3 days ago
Photo: “Silky Ant - Formica subsericea” by Christina Butler, via Wikimedia Commons, licensed under CC BY 2.0.
Shiny, black and lightning fast, Formica subsericea is one of the most common field ants in eastern North America. The silky field ant is a close cousin of our own UK silky ant, and just as much fun to watch.
Drop food in the outworld and the workers dash out to grab it, then vanish again in a flash. This guide explains Formica subsericea care step by step, from a founding queen to a thriving colony.
Formica subsericea is a North American ant, and Best Ants UK does not sell it. We don't encourage importing ants from abroad. This guide is for keepers where the species is native, and for anyone curious about it.
We have kept ants since 1997, and the care rules here are the same ones we use for our own colonies every day.
👉 In a hurry? Download our free Formica subsericea care sheet (PDF) or open the Formica subsericea care sheet page for the key facts at a glance.
Formica subsericea at a Glance
Also known as: the silky field ant, or black field ant
Origin: eastern and central North America, from southern Canada to northern Mexico
Keeping level: Beginner
Queen: 10 to 12mm, jet black with a silvery sheen
Workers: about 5 to 8mm, all one shape, black and silky
Colony: usually one queen, several thousand workers when mature
Nest temperature: 22 to 28°C, best at 24 to 26°C
Nest humidity: 50 to 60%
Workers before moving into a nest: 10 minimum, 15 to 20 recommended
Winter: a natural winter rest, never in a fridge
Escape risk: very fast climbers, so a PTFE barrier is a must
Meet the Silky Field Ant
In the wild, silky field ants nest in open ground: fields, meadows, lawns, roadsides and the sunny edges of woods. They build their nests in soil, often under stones or with a small mound of earth at the entrance.
Fine silvery hairs give their black bodies a soft, silky shine, which is where the name comes from. Workers are quick, nervous and shy, and they dart for cover at the first sign of danger.
They feed on honeydew from aphids and on small insects, alive or dead. They have no sting, but they can spray a tiny puff of formic acid, which is harmless to people.
Like the UK silky ant, they are a favourite host of slave-making ants such as Polyergus, which raid their nests for brood. New queens fly in summer, mostly in July and August, then seal themselves away to raise their first workers alone.
When Your Ants Arrive
The most important step: leave the parcel completely unopened, exactly as it arrived, at room temperature for 5 hours. The ants must adjust to your home's temperature slowly, because abrupt temperature changes make ants seriously unwell.
After the 5 hours, check the queen is safe and sound. Then leave the colony in its original packaging, with the test tube still in its tin foil and wrapping.
Put it somewhere quiet and still, away from daily household activity. Normal daylight is fine, but never direct sunlight.
Give the colony 4 to 5 days of complete rest, with no food. A good supplier feeds the ants before dispatch. Use this time to set up and water the nest. 👉 Our step-by-step ant farm setup guide shows you exactly how.
Still workers or a motionless queen after delivery are almost always delivery stress. Look at the queen's antennae: moving antennae mean she is fine. Almost all recover within 4 to 5 days.
Life in the Test Tube
Keep the colony in its test tube until it has at least 10 workers. 15 to 20 is even better. Moved earlier, the workers often abandon the queen in the bigger space, and the colony can fail.
A queen on her own still needs a little food, even though she could live on her reserves. Once a week, give her a tiny drop of protein jelly, about half a grain of rice, on a small flat piece of tin foil inside the tube, next to the dry cotton stopper.
In our experience a fed queen raises her first workers faster, and the queen and colony do far better afterwards. Keep her tube wrapped in its foil and disturb her as little as possible.
With warmth and protein, the brood takes about 6 weeks from egg to worker. The first year is slow, with dozens of workers by year two and hundreds or more after that.
Moving Into the Ant Farm
When the colony is ready, connect the test tube to the nest with the delivery tin foil still on. Leave it like that for 14 days.
Then slide the foil back about 1mm every day until the tube is fully exposed to daylight. Bit by bit, the tube becomes the bright spot and the dark nest becomes the safe home.
If the ants haven't moved 2 days after the tube is fully exposed, wrap the foil back on, wait another fortnight and repeat. Moving in happens on the ants' own time: anywhere from a couple of days to 6 months.
Once the colony has moved, leave the old test tube connected for at least another 14 days, as ants sometimes leave brood behind.
The red filter and black cover stay on the nest all the time. You can lift the black cover once a day for 2 to 3 minutes, ideally at night, and take the red filter off once a week for 2 to 3 minutes. Take colony photos no more than once a month.
The Best Ant Farm for Formica subsericea
Silky field ants are big for a field ant and love to run, so give them a nest with room to grow and a good-sized outworld for foraging.
👉 Our top pick is the A7 Plus ant farm kit. Its pre-installed digital meter shows nest temperature and humidity at a glance, which keeps watering and heating simple and mistakes to a minimum.
Place the ant farm in normal daylight, never direct sunlight. Avoid windows, radiators and heaters, vibrating surfaces, speakers and TVs, and rooms with strong smells such as the kitchen.
Temperature and Heating
Keep the nest at 22 to 28°C. The brood grows best at 24 to 26°C. The workers like to choose their own spot, so always give them a warmer and a cooler part of the nest.
In a cool home, where the room stays around 20°C or below, the brood takes far longer to develop. 👉 There, an Advanced Heating System Small 4W set to 24°C helps the colony thrive.
The heat mat goes under one quarter of the nest only, on the side opposite the watering area. Never heat the whole nest.
In the outworld, aim for about 18°C overnight up to 28°C by day. By day it should ideally match the nest or be a degree or two cooler. If the nest is heated, warm the outworld too, because a big gap confuses the ants.
Water and Humidity
Keep the nest humidity at 50 to 60%, and never let it dry out completely. Use distilled or purified water only. Never use tap water, rainwater or bottled mineral water, even boiled: they cause mould and fungus, which is deadly for ants.
Water the nest with the pipette provided. Pour slowly, a few drops at a time, through the watering hole. Stop as soon as 1 or 2 drops appear inside the nest. That is how you know it is done correctly.
Water about once a week, a little more in summer and a little less in winter. With a meter, simply water when the nest humidity drops below 50%.
Never water the outworld. Keep it dry, at about 50% humidity, like an average UK home.
Feeding Your Silky Field Ants
Silky field ants are keen hunters, and a growing colony has a big appetite for protein. Feed twice a week, in small amounts, in the outworld only. Remove leftovers after 2 days to stop mould.
🥩 For the queen and brood, give 👉 Protein Jelly or 👉 Cricket Mash. Keep protein jelly in the fridge at all times. The larval stage is short, so feed a little extra protein when you see larvae.
🍯 For energy, give our 👉 organic ant honey or 👉 Ant Nectar, which has even more carbohydrates than honey. Both are far better than sugar water or home-made mixes.
Serve food on a small piece of tin foil or in a 👉 small feeding dish, so leftovers are easy to lift out.
Live food, such as crickets or locusts, is only for big, established colonies, never small ones. Always scald it first: wearing gloves, hold it with tweezers in just-boiled water (above 90°C, no longer bubbling) for 10 to 15 seconds.
Then cut it in half only, and serve it in the outworld.
Keep Mites Out of Your Colony
Blood-sucking mites are one of the biggest dangers for any ant colony, and they are not rare. They often arrive with bird seed from local shops, dried mealworms, and live food bought from pet shops or online marketplaces.
Dried mealworms are also useless as ant food. Buy ant food only from established, reputable ant-keeping suppliers. At Best Ants UK we clean our foods in several ways before dispatch and check every colony twice a month.
Now and then, look at your queen with a magnifying glass. Tiny white or reddish specks on her joints and legs, together with ants dying fast, are a warning sign of blood-sucking mites.
Stopping Escapes
Silky field ants are among the fastest climbers you can keep, so escape prevention is a must. Paint a band of 👉 PTFE Fluon escape barrier around the top inner edge of the outworld lid. The ants slip off it and can't climb out.
PTFE wears off as the ants keep testing the same spots. For a small colony of up to about 100 ants, reapply it roughly every 4 weeks. For 300 to 500 ants or more, reapply it about every 2 weeks.
Never shake the bottle, because it foams. Roll it gently in your hands instead.
Winter Care
Silky field ants come from places with cold winters, and they have a natural winter rest. Their development slows down from late autumn whatever you do, because their biological clock can't be tricked. We never hibernate queens in their first year.
A full hibernation is only safe at a steady 5 to 10°C, roughly from November to the end of March. That needs a specialised hibernation unit with precise temperature control. Never use a fridge, shed or garage, and avoid any abrupt temperature change.
Without a hibernation unit, keep the colony at room temperature all winter. Feed less, but never guess. At 17 to 22°C, give about a third of the summer amount. At 22 to 26°C, give about half. In full hibernation, give fresh water only and no food.
Can I Release My Ants?
Never. Formica subsericea is not a UK ant, and a colony raised indoors won't survive outside. If you can't keep your colony any more, 👉 visit our ant adoption page and let us know. We'll see whether we can take it in.
Frequently Asked Questions | FAQ
Is Formica subsericea good for beginners?
Yes, it is a hardy, forgiving species that grows well with steady warmth and plenty of protein. The workers are very fast and shy, so a PTFE barrier on the outworld is essential.
Can I buy Formica subsericea in the UK?
Best Ants UK does not sell Formica subsericea. It is a North American ant, and we don't encourage importing ants from abroad. Its close UK cousin, the silky ant Formica fusca, is a great native alternative.
How many workers before moving Formica subsericea into a nest?
At least 10 workers, and 15 to 20 is even better. Moved earlier, the workers often abandon the queen in the bigger space and the colony can fail.
What temperature do silky field ants need?
Keep the nest at 22 to 28°C, best at 24 to 26°C. In most UK homes an Advanced Heating System set to 24°C under one quarter of the nest keeps the brood growing.
Do Formica subsericea hibernate?
They have a natural winter rest. A full hibernation is only safe at a steady 5 to 10°C in a specialised hibernation unit, never a fridge, shed or garage. Otherwise keep them at room temperature; they slow down anyway. We never hibernate queens in their first year.
What do Formica subsericea eat?
Protein Jelly or Cricket Mash for the queen and brood, plus organic honey or Ant Nectar for energy, twice a week in the outworld. Growing colonies are big protein eaters.
How big does a Formica subsericea colony get?
A mature colony can reach several thousand workers. Most colonies have a single queen, although some wild populations have several.
Ready for Your Own Formica Colony?
A silky field ant colony soon fills its first nest with fast, shining workers. When yours needs more room, 👉 the A6 ant farm kit with meter gives a bigger Formica colony space to grow, with a digital meter to keep care simple.
Print this guide and keep it next to your ant farm, so the essentials are always close. 👉 Explore all our free ant care sheets.
