Sphinxes prefer warm desert climes and the hills nearby, both for the comforting warmth and the pleasant solitude. The more intelligent sphinxes have contrary social natures, alternately craving conversation and isolation as the mood strikes them. Indeed, a bored or irritated sphinx often takes leave in the midst of discussion, or perhaps slays and devours its petitioners out of sheer annoyance.

While sphinxes as a race are not truly immortal, they are fantastically long-lived, save for the violent hieracosphinxes, who rarely survive their second decade. Unless slain by accident, violence, or misadventure, other sphinxes seem to pass on only when they have at last wearied of living and will themselves to die. The older a sphinx is, the less it needs consume. The oldest of sphinxes dine perhaps once per century, making them ideal guardians for monuments, temples, and tombs.

Sphinxes prefer to converse in their own tongue, but most speak the languages of humans and dragons as well. Addressing a sphinx in its own language with all due politeness and deference goes a long way to ensure peaceful conversation. All sphinxes save hieracosphinxes enjoy stimulating conversation, though for such long-lived creatures their memory for detail is sadly lacking. In some cultures, “a mind like a sphinx” serves as a sarcastic alternative to “scatter-brained.”

Though sphinxes have a reputation for loving riddles, in truth, only gynosphinxes truly enjoy them. Androsphinxes prefer lofty philosophical discussions, while criosphinxes prefer worldly topics or fawning praise. Hieracosphinxes rarely converse at all, and respond only to threats from creatures more powerful than they are.

Neighboring humanoids generally adopt a policy of avoiding local sphinxes, as the creatures grow increasingly irritable each time their solitude is invaded. Even so, once a sphinx's lair is known, it can expect a steady flow of visitors in search of the fabled wisdom of its race. Some sphinxes move to quieter abodes once the interruptions become too much to bear; others devour a few of the more irritating supplicants until the visits cease.

Sphinxes have peculiar breeding habits, contributing in no small part to their scarcity and the strange diversity of their species. Indeed, matters of mating occupy much of the thoughts of all of the sphinxes save the prudish androsphinxes. The female gynosphinxes have nothing but scorn for animal-headed sphinxes, craving only the attentions of the masculine androsphinxes. For their part, androsphinxes consider petty rutting a waste of time and energy, both of which are better spent on loftier pursuits than the fleeting pleasures of the flesh. Criosphinxes and hieracosphinxes alike lust after gynosphinxes. The former abase themselves and attempt to curry favor with lavish gifts. Hieracosphinxes scorn any such civilized gestures, and mate by force on the rare occasions they have a female at their mercy.

From these rare couplings, two to four sphinxes of any type may be born, regardless of the breed of the parents. Instead, the nature of the coupling itself influences the species of the resulting offspring. From those rare matings engendered by love or respect, androsphinxes and gynosphinxes are born. Those couplings motivated by carnal lust or selfish urges most often produce criosphinxes. Hieracosphinxes come from acts of hate and violence, and their disgusted mothers quickly abandon them to the mercy of the elements, lest the young turn against them. Of all the males, only the criosphinx willingly helps rear its own young, often as part of the bargain for mating in the first place.

People of the desert sometimes honor the sphinx's form by crafting great stone sphinxes, often bearing the faces of their own rulers and nobles. Legend holds the first such monuments were modeled on the eldest and greatest of sphinxes, paragons of knowledge and wisdom far larger in size than any common sphinx. The oldest and largest of these sphinxes settled into the desert sands when at last they tired of immortality, and as they passed into their final sleep, their bodies became as sandstone.

These elder sphinxes may be androsphinxes or gynosphinxes, or very rarely criosphinxes. They have at minimum the advanced template, many additional Hit Dice, and a size of at least Huge (and more often Gargantuan or Colossal). They can use commune, contact other plane, and legend lore as spell-like abilities once each per day (CL equals the sphinx's CR), and frequently possess other powers and special attacks. Many such sphinxes can enter a state of stony suspended animation that resembles the freeze special ability, though they cannot easily rouse themselves from such slumber. Other sphinxes, even the bestial hieracosphinxes, defer to elder sphinxes in all matters, treating them almost as gods.