The Equestrian changeling (Equus equestrianensis changelingis) is an equine-shaped creature with insectoid characteristics, native to the Badlands region of the southern part of the continent of Equestria, located on its eponymous planet. It is noteworthy for its unusual diet of others' care and affection, and its ability to change its physical appearance at will, similar to the European mythological creatures of the same name.
Its outer body is a black exoskeleton, resembling a hybrid of a beetle's and an ant's, with a blue plate on its back from its withers to its rump, where it rests its cyan webbed wings. Each of the four legs that sprout from its body are riddled with several holes on the sections nearer to their hooves, which are mostly covered with their bodies' exoskeletal substance (save for the soles, which are of a fleshy material for the occasional hoof-holding). Two mane-like fins course from its bare head down its upper neck, and a curved horn protrudes from its forehead for its magical abilities. Its teeth resemble those of their "normal" Equestrian pony counterparts, but with two long fangs it uses (alongside all four legs) to attack enemies or defend itself. A blackish-grey webbed tail sprouts out on its rump.
The height of the average changeling, from legs to withers is approximately 41 inches, around the same height as those of the Equestrian and Shetland ponies. Its average weight is around 573 lbs. , a bit lighter than an Equestrian pony's 800~1,400 lbs. (800~1,000 for Unicorns, 1,100~1,290 for Earth Ponies, and 1,400 for Pegasi)
The changeling's diet is mostly on "love", which is usually affectionate feelings created by other beings, picked up by receptors on the neck that converts those "feelings" into chemicals that its stomach digests and nourishes its body. That same "love" is more stronger if it is from a more sapient being, and even more if the changeling itself is the recipient of said "love". However, "love" produced by another changeling does not provide enough strength to sustain one changeling, although the queen's "love" is roughly equivalent to the amount produced by only a single Equestrian alicorn. Changelings can still eat other kinds of food, such as berries, carrion, shrubs, grass, flowers, and garbage, although all other kinds of food are not as "delicious" or "strengthening" as others' affection. Contrary to popular belief, they do not hunt, kill, and eat other creatures (unless they are served in a platter or found as corpses in a garbage dump), nor do they ever practice cannibalism (which they consider abhorrent); when famished, they fly off in search of food.
Changelings make cricket-like chirps, flash their horns in a code, dance at the air, awkwardly gesture with their front hooves, and buzz their wings in different tempos to communicate with each other. They can also speak languages (especially Common Equestrian/"English", spoken in many universes and dimensions, and an unwritten pseudo-Greek dialect), although not as often as their queen does.
All of the approximately three and twenty million changelings naturally live in an underground hive, where they follow a hierarchy, similar to many insect-based species. On the top is the queen, who ultimately rules and commands the movement, actions, and decisions of the hive. Under her are the "elder" changelings (palaeyo-i), from whom she appoints as among a hooffull of "captains" to guide her numerous soldiers. They may look just like any other changeling, but aside from their occasional bluish-black armor, they are more experienced and skilled than the rest in fighting, strategy, seducing, disguising, and love-gathering. At the bottom of all this is the majority of the changeling horde, those unfortunate ponies from all over Equestria who were already captured and forcibly transformed into such creatures, having with only a little of their original personalities with them - these reserve "soldiers" and "gatherers" also build the hive alongside their slaves, and produce its characteristic green goo structures. Below this raucous dark winged mass are tens of thousands of enslaved ponies (and every non-pony captured), willing and unwilling alike, who provide the nowadays-unsatisfying amounts of affection the changelings need to sustain themselves.
Last but not least is the basis of their name: their ability to change their physical appearances, and even some of their structure in the process. Each changeling does this by thinking of itself as another pony, and green flames burst from its legs, sweeping upwards until it has become a doppelgänger or an imposter of its target. They mainly do this to infiltrate target settlements for prey, to fool ponies into following or loving them, and for scouting, spying, or ambushing and assassinating enemies.