How to Care for Pheidole rhea | The Giant Big-Headed Ant Guide
Photo: Jake Nitta, via iNaturalist, licensed under CC BY 4.0.
Pheidole rhea is the giant of the big-headed ants. From the mountains of Arizona, New Mexico and Mexico, it has three sizes of worker, from tiny minors to supermajors with heads like little helmets.
A warm, well-fed colony grows astonishingly fast, and watching the supermajors crush seeds is unforgettable. This guide explains Pheidole rhea care step by step, from a queen in a test tube to a colony of thousands.
Pheidole rhea is a North American ant, and Best Ants UK does not sell it. North American ants may be illegal or impossible to import into the UK, and we never encourage importing ants. This guide is for keepers where it is native, and for anyone curious.
We have kept ants since 1997, and these are the care rules we use for our own big-headed ants.
👉 In a hurry? Download our free Pheidole rhea care sheet (PDF) or open the Pheidole rhea care sheet page for the key facts at a glance.
Pheidole rhea at a Glance
Also known as: the giant big-headed ant
Origin: south-eastern Arizona and south-western New Mexico, into Mexico
Sold by Best Ants UK: no, it is a North American species
Keeping level: Intermediate
Queen: very large, about 16 to 18mm, dark reddish brown
Minor workers: 3 to 4.5mm, yellowish to reddish brown
Majors: 5 to 10mm, with big, blocky heads
Supermajors: 11 to 13mm, with enormous heads
Colony: one queen, tens of thousands of ants when mature
Nest temperature: 26 to 30°C
Nest humidity: 50 to 70%
Workers before moving into a nest: 50+
Winter: no full hibernation, never below 15°C
Escape risk: high for the minors, so a PTFE barrier is a must
Meet the Giant Big-Headed Ant
In the wild, Pheidole rhea lives on grassy, rocky slopes and upland plateaus, often well over 1,000 metres above sea level. It nests deep in the soil, often under large rocks that keep the nest at a steady temperature.
A colony has three kinds of worker. The minors are the busy all-rounders: they forage, clean and look after the eggs, larvae and pupae (the brood). The majors help to cut up food and dig.
The supermajors are the stars. Their heads are enormous, and their jaws crush hard seeds and insects that the smaller workers can't open. They also guard the nest entrance. Colonies keep making bigger soldiers as they grow.
Pheidole rhea is bold and defends its food fiercely. In the wild it eats seeds, dead insects and sugary liquids. Mating flights happen in the summer rainy season, mostly from June to August.
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
Every Pheidole needs far more workers than most ants before it moves into an ant farm, and rhea is no exception. Its minors are small, so even a whole young colony takes up very little space. Keep it in its test tube until it has at least 50 workers.
Moved too early, a small colony is lost in the bigger space: the workers abandon the queen and the colony dies. The same 50+ rule applies to a queen on her own.
A queen on her own still needs a little food. 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.
A rhea queen also needs warmth: at normal UK room temperature her brood barely develops. With heat, the brood takes about 3 to 6 weeks from egg to worker, and the bigger castes take longer. The first supermajors may take several months to appear.
Moving Into the Ant Farm
When the colony is big enough, 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. Ants sometimes leave a little 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 once a month at most.
The Best Ant Farm for Pheidole rhea
Pheidole minors squeeze through the smallest gaps, so their home must be well made and escape-proof. A young colony also feels safest in a nest it can fill. Plan for more room as it grows, because rhea colonies get big fast.
For every Pheidole we recommend the A7 Plus ant farm kit only (you will find the link at the end of this guide). Its small nest suits tiny workers, and its pre-installed digital meter shows nest temperature and humidity at a glance.
Place the ant farm in normal daylight, never direct sunlight: the sun can overheat a nest within minutes. Avoid windows, radiators and heaters, vibrating surfaces, speakers and TVs, and rooms with strong smells such as the kitchen.
Temperature and Heating
For this species, heating is the most important part of the whole setup. Keep the nest at 26 to 30°C. At normal UK room temperature the colony barely grows. Never let the nest go above about 32°C.
A UK home is far cooler than that for most of the year. 👉 The Advanced Heating System Small 4W holds a steady warm spot with its digital thermostat. Set it to 28°C, in the middle of the range.
The heat mat goes under one quarter of the nest only, on the side opposite the watering area. The ants can then pick the spot they like best. 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. The nest is heated, so warm the outworld too: a big gap confuses the ants.
Water and Humidity
Keep the nest humidity at 50 to 70%. 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. A heated nest dries faster, so check it often. 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. A watering test tube in the outworld gives the workers a safe drink. Never let it run dry: this species dries out quickly.
Feeding Your Giant Big-Headed Ants
Pheidole rhea is a big eater, and a well-fed colony grows at an amazing speed. Feed twice a week, in small amounts, in the outworld only. Remove leftovers after 2 days to stop mould.
🌾 Seeds are an important part of the diet. Give our 👉 harvester seed mix on a piece of tin foil or in a 👉 small feeding dish in the outworld. Never put seeds straight on the substrate: they sprout, and sprouted seeds are harmful.
🥩 For the queen and brood, give 👉 Protein Jelly or 👉 Cricket Mash. Keep protein jelly in the fridge at all times. A big colony needs plenty of protein.
🍯 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 and keep the busy minors going.
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. Never chop it smaller, and skip mealworms. The soldiers drag small pieces into the nest, the minors can't carry the remains back out, and mould follows.
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 and off-licences, dried mealworms, and live food from pet shops or online, where about half carries mites.
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 before dispatch, freeze our seeds below -60°C in a special freezer, 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
Rhea minors are small and quick, 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; roll it gently instead.
Winter Care
Pheidole rhea doesn't need a full hibernation. You can keep the nest at 26 to 30°C all year, and the colony keeps growing. It still slows down a little in winter, because its biological clock can't be tricked.
Many keepers give an established colony a gentle rest at about 18 to 20°C for around 2 months in winter. Never let it get colder than 15°C, and we never rest queens in their first year.
Never put ants in a fridge, shed or garage, and avoid any abrupt temperature change. Feed less during a rest, but never guess. At 17 to 22°C, give about a third of the summer amount. At 22 to 26°C, give about half.
Can I Release My Ants?
No. A colony raised indoors won't survive outside, and a North American ant doesn't belong in the wild here. If you ever 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 Pheidole rhea good for beginners?
No, it is an intermediate species. The colony grows fast, eats a lot, needs real warmth all year and has tiny minors that need a PTFE barrier. Start with a beginner species such as Lasius niger or Messor barbarus first.
Can I buy Pheidole rhea in the UK?
Best Ants UK does not sell Pheidole rhea. It is a North American ant, and it may be illegal or impossible to import into the UK. We never encourage importing ants.
What is a supermajor?
Pheidole rhea has three worker sizes: small minors, big-headed majors and giant supermajors with enormous heads. The supermajors guard the nest and crush hard seeds that the others can't open.
How many workers does Pheidole rhea need before moving into a nest?
At least 50 workers. A smaller group is lost in an ant farm and the colony can fail. Keep it in the test tube until it reaches 50. The same rule applies to a queen on her own.
What temperature do Pheidole rhea need?
Keep the nest at 26 to 30°C. At normal UK room temperature the brood barely grows, so use an Advanced Heating System set to 28°C under one quarter of the nest.
Do Pheidole rhea hibernate?
No full hibernation is needed. Many keepers give an established colony a gentle rest at about 18 to 20°C for around 2 months in winter. Never below 15°C, and never in a queen's first year.
What do Pheidole rhea eat?
Seeds, protein and sugars. Give our harvester seed mix on tin foil or a feeding dish, Protein Jelly or Cricket Mash, and organic honey or Ant Nectar, twice a week in the outworld only.
Ready to Start Your Own Big-Headed Ant Colony?
👉 Start with the A7 Plus ant farm kit. Its small nest suits tiny workers, its pre-installed digital meter shows temperature and humidity at a glance, and if you already have your ants, choose its Nest + Outworld option. 👉 Explore all our free ant care sheets.
