👯 Pets That Should Never Live Alone — and What a Pair Really Costs

Here is a cost that almost no pet-care page tells you about up front: for a lot of popular small pets, the correct number to buy is two. Not because two is nicer, but because one is a welfare problem — and in some countries, a legal one.

We rated all 50 pets on this site for whether they need company of their own species. 22 of them do. Below is the full list with the real monthly cost of keeping them properly, so nothing surprises you at the checkout.

The 22 pets that shouldn't live alone

The Group size column is the smallest group a pet should be kept in. For the first group below the monthly bill really does multiply by it — each animal eats and sees a vet separately. For the second it does not: those pets share one tank or bin, so the figure shown already covers all of them.

Pet	Group size	Monthly cost	What you actually pay
🐾 Pets where a friend doubles the billEach animal eats, drinks and sees a vet separately, so the cost really does multiply.
Mouse	At least 2	$8–$18/mo each	$16–$36/mo
Gerbil	At least 2	$10–$20/mo each	$20–$40/mo
Rat	At least 2	$15–$30/mo each	$30–$60/mo
Parakeet & Small Birds	At least 2	$15–$35/mo each	$30–$70/mo
Degu	At least 2	$15–$35/mo each	$30–$70/mo
Guinea Pig	At least 2	$25–$45/mo each	$50–$90/mo
Chinchilla	At least 2	$25–$50/mo each	$50–$100/mo
Quail	At least 3	$15–$35/mo each	$45–$105/mo
Rabbit	At least 2	$30–$60/mo each	$60–$120/mo
Sugar Glider	At least 2	$30–$60/mo each	$60–$120/mo
Chicken	At least 3	$20–$45/mo each	$60–$135/mo
Ferret	At least 2	$40–$80/mo each	$80–$160/mo
Duck	At least 3	$25–$55/mo each	$75–$165/mo
Goat	At least 2	$40–$90/mo each	$80–$180/mo
Mini Pig	At least 2	$50–$120/mo each	$100–$240/mo
Pony	At least 2	$150–$400/mo each	$300–$800/mo
🪴 Pets that share one habitatOne tank or bin covers them all, so the monthly figure already includes the whole group.
Ant Farm	At least 10	$2–$8/mo	Same habitat, same bill
Isopods	At least 10	$3–$10/mo	Same habitat, same bill
Hissing Cockroach	Pair or group	$5–$15/mo	Same habitat, same bill
Shrimp & Snails	At least 10	$8–$20/mo	Same habitat, same bill
Hermit Crab	At least 3	$10–$25/mo	Same habitat, same bill
Goldfish	At least 2	$15–$40/mo	Same habitat, same bill

In Switzerland, some of these are illegal to keep alone

Switzerland is unusual in writing this into law. Article 13 of its Animal Protection Ordinance says animals of social species must be given proper company, and the rules that follow from it are a good sanity check on your own plans: guinea pigs, mice, gerbils, rats, degus, chinchillas, ferrets, budgies, lovebirds, parakeets, parrots, macaws, cockatoos, canaries, finches, and Japanese quail all have to be kept with company.

Two things stand out. The first is how far it reaches beyond the obvious pets — Swiss authorities also say goldfish should be kept in groups, because they are a shoaling fish and the lone fish in a bowl is a genuinely poor life. That one is guidance rather than a ban, but it makes the point. The second is who is not on the list: the Syrian hamster, which Swiss regulations explicitly describe as a loner that should be kept alone. Sociability is a fact about the species, not a general rule about kindness.

When a friend doubles the bill — and when it doesn't

This is the distinction that matters for your budget, and it splits the list cleanly in two.

Animals that eat, drink, and see a vet individually really do cost twice as much in a pair. Two guinea pigs eat two guinea pigs' worth of hay and pellets and need two guinea pigs' worth of vet care. The same goes for rabbits, rats, mice, gerbils, chinchillas, degus, ferrets, sugar gliders, and budgies. For chickens, ducks, and quail the practical floor is three, not two, so the multiplier is bigger again.

Tank and colony species are the happy exception. Goldfish, shrimp and snails, hermit crabs, hissing cockroaches, isopods, and an ant farm all share one tank, one bin, one heater, and one bag of food. Their monthly figure already covers the group, so a second animal costs almost nothing to run. What it does cost is space: a second goldfish wants roughly another 10 gallons of water, and that is a one-off tank purchase rather than a monthly bill.

One thing the monthly figure never doubles is housing. A bonded pair shares a cage — they need a bigger cage than a single animal, not two cages. Our setup cost guide covers that side of it.

The pets that are genuinely happier alone

If your budget or your space really only stretches to one animal, do not compromise by getting one of the social species. Get a solitary one instead. Genuinely solitary pets include the Syrian hamster, the betta fish (two males will fight to the death), the hedgehog, and most reptiles — geckos, bearded dragons, snakes, chameleons — along with tarantulas, scorpions, praying mantises, and crayfish, several of which will simply eat a tankmate. A single pet from this list is a better pet than a lonely one from the list above.

You can't just add a second one

The last thing worth knowing is that pairing is a process, not a purchase. Small social mammals are territorial about their own space, so two adults introduced by dropping one into the other's cage will usually fight. The standard approach is neutral territory, short supervised sessions, over days or weeks, and even then not every pairing takes — same-sex pairs of siblings are the easiest, and unneutered mixed pairs will simply give you babies.

There is a shortcut, and it is the best advice on this page: adopt an already-bonded pair from a rescue. Guinea pigs, rabbits, and rats all turn up in rescues in bonded pairs, the hard part is already done, and it is almost always cheaper than two animals from a shop. Our adopt, don't shop guide has more on finding one.

Work out what fits

The Pet Finder has filters for both sides of this: "needs a friend" if you like the idea of a pair, and "happy on its own" if one is all you have room for. Costs on every pet page say whether the figure is per animal or already covers the whole group, so you know the real bill before you decide. You can also take the free pet quiz or compare the running costs of all 50 pets in how much do pets cost.

🛒 Recommended supplies

Hand-picked gear for this guide. Affiliate links — we may earn a commission. The $/$$/$$$ badges are a rough budget guide, not live prices.

❓ Common questions