Scyther is mostly based on the mantis. Like most Pokémon, Scyther is a simplification of the creature, albeit with giant killer scythes to Pokémon-ifiy it.

There are about 2,400 different species of mantis, belonging to the family Mantidae. Mantises in general are commonly called "praying mantises" because their bent forelegs look as if they're praying. Mantises use these limbs to capture prey, making it fitting that Scyther's are replaced with scythes. Mantises have two sets of wings, one for protection and camouflage, the other for limited flight. Mantises can see up to 20 meters, and are generally diurnal.

Mantises generally prey on other insects, but large species of mantises can prey on larger creatures like snakes, birds, frogs, and rodents. Mantises rely on camouflage to defend themselves, blending in with their surroundings to better ensnare their prey. They can also slash at predators with their forelegs — inspiration for Scyther, perhaps?

One of the most notable traits of the mantis is their proclivity for sexual cannibalism. Typically, the female bites off the male's head during intercourse. Sorry, man.

All of these features fall in line with things talked about in Scyther's Pokédex entries. The one thing about Scyther that doesn't come from the mantis is its head: it looks more like a reptile's or dragon's head, and nothing like a mantis.

If you'd like to see images of mantises, and learn more about them, I suggest Wikipedia. Bugs are not my thing; I like Scyther in spite of its buggy aspects, not because of them.