The classical posture vocabulary is populated almost entirely by large animals: the eagle, the cow, the bull, the camel, the lion, the peacock, the crocodile, the tortoise. The locust is the one insect, and its presence says something about how the naming worked. What the compiler needed was a creature whose characteristic silhouette a reader would recognise instantly, and a grasshopper at rest, with its hind legs folded high behind a low body, is as distinctive a shape as any of the larger animals offer.
The locust also carries an association the manuals do not use. In agricultural South Asia, as elsewhere, locusts are the swarm that destroys a harvest, and they appear in that role in literature and in ritual concerned with averting calamity. Nothing of that reaches the posture entry, which names the shape and stops. The atlas records the resemblance the text implies and does not import a symbolism the text does not claim.
Reading the animal names as a group rather than one at a time is the useful move here. They are drawn from what a person in medieval North India would see in a day: livestock, birds, temple carvings, the creatures of a river bank and a field. That is a vocabulary of resemblance built from ordinary life, which is exactly what an oral technical tradition needs if a list of thirty two shapes is to be carried in memory.