The short answer for sugar gliders
Yes — a sugar glider needs at least one other sugar glider, and this is one of the least negotiable needs in small-pet keeping. Gliders are colony animals who spend their wild lives inside a family group, and a glider kept alone is not simply a bit lonely: lone gliders are known to slide into depression, lose interest in food, over-groom themselves raw, and in the worst cases injure themselves. Experienced keepers and rescues treat a same-species companion as part of the basic setup, as essential as the tall cage and the sleeping pouch.
How colony life shapes a glider
A wild glider's day is organised around its group. The colony sleeps through daylight hours packed into a shared nest, each animal layered against the warmth and scent of the others, and scent is identity — colony members mark and recognise each other, and the shared smell is the group's passport. At night they forage, glide and call to each other, keeping contact across the trees. Bonding pouches, colony grooming and that constant vocal check-in are not habits a glider can redirect onto a human schedule. Your glider may bond strongly to you, ride in your pocket and trust your hands completely, and still be missing the animal it needs at four in the morning when the colony would be awake and you are not.
What loneliness does to a single glider
The decline of a lone glider usually starts quietly. Appetite drops or turns picky; the glider sleeps at odd hours, calls at night with the bark that normally keeps a colony in touch, or goes the other way and becomes flat and silent. Over-grooming follows in many cases — fur pulled from the chest, tail or belly — and self-inflicted wounds are the recognised end of that road if nothing changes. None of this is spite or bad behaviour, and it does not reliably reverse with more handling, bigger toys or a larger cage, because none of those is the missing thing. The missing thing is another glider, and providing one early is far easier than rehabilitating a glider who has already started to fail.
Pairing gliders the right way
Plan for company from the beginning: two gliders from the same colony, or a pair already bonded, is the smoothest start. Introducing strangers takes more care — separate cages side by side so the animals can see, hear and smell each other, pouches swapped between cages to trade scents, then short supervised meetings in neutral space before any shared housing. Males should be neutered unless you are deliberately and knowledgeably breeding, both to prevent joeys and to soften territorial behaviour. Sex, age and temperament all feed into compatibility, which is why rescues that bond gliders before rehoming are such a good route for a first glider: the colony work is already done, and you take home a pair who have chosen to sleep in the same pouch.
The records a pair of gliders generates
Two gliders means two sets of everything veterinary: weights to track, neutering notes, parasite checks, and the diet and health history an exotics vet will ask about at every visit, often in an emergency, at night, when remembering which glider had which issue last spring is not realistic. Keeping the pair's paperwork bundled rather than scattered is part of responsible colony keeping. A KinsLe Pet Passport does that bundling for you — both gliders' records held together in one portable packet, ready to hand over at vet visits, boarding or any handoff, so each animal's history travels with the pair it belongs to.