Arms or Legs?

 

Common Baskettail

Like all insects, dragonflies are considered to have six legs. Though they don't walk, they use those six limbs in various ways that make me wonder about the difference between an arm and a leg.

Black-tipped Dasher

When alighting on earth many dragonflies hang rather than stand. That raises the question of whether they're employing feet, hands, paws, claws, or some special solution I don't have an adequate word for.

Eastern Forktail

They do grasp, aided by flexible joints and barbs for holding onto things. But then grasping involves the kind of dexterity I associate more with arms than legs.

Blue Dasher female

Dragonflies catch and consume their prey in midair. Their limbs are configured like basket staves to facilitate scooping and clutching, rather than a linear arrangement advantageous for walking. The limbs to the rear appear to be more weight-bearing, the ones to the front more nimble for functions close to the mouth and for settling encounters with friend or foe.

In this way a dragonfly's limbs are specialized, like with many other animals. However tradition has categorized very few of even the most supple limbs as arms, in that exalted class with primates and octopi. Not even squirrels and raccoons, with their superior dexterity, have been so designated, presumably because they move about on all fours. Nevertheless, along with dogs, cats, and horses, they have skeletal parallels with us: powerful hind limbs that extend from hip sockets and articulate at knee joints; and relatively mobile front limbs fluidly connected at the shoulder, with flexible elbows and wrists. These anterior limbs are thought of as forelegs rather than arms, terminating in something not quite as marvelous as a hand.

A Stripe-legged Robberfly eating a captured Rust Fly

Just how adroitly dragonflies use their limbs on the hunt is hard to say, since they don't bring their prey back to an observable perch. They most likely operate like this robber fly, which launched from a stationery platform, landed with its victim on a similarly hexagonal group of grasping‒legs? ‒and fed itself handily.

Painted Skimmer

An intriguing diversity of solutions goes to satisfy the common needs of creatures top to bottom in the animal kingdom. Arms are certainly a marvelous development from legs, but wings! there's an aspiration.