You might think an insect with an extra pointy derriere would pack a fearsome sting, but you'd be wrong. The extended rear appendage of the crown-of-thorns wasp is not a stinger but an egg-laying organ, the ovipositor, used to reach beetle grubs chewing through the wood below. Young wasps develop as ectoparasites of beetles in their burrows. Should this wasp take a stab at you, you'd feel as though tickled by a toothpick. Nothing more.
Why is this called a crown-of-thorns wasp? Have look at the head:
Like the vast majority of wasps, Megischus is not aggressive. In fact, a challenge I faced photographing these delicate insects was their tendency to flee when the camera approached.
photo details (top):
Canon 100mm f2.8 macro lens on a Canon 6D
ISO 400, f/14, 1/160 sec
diffuse overhead speedlite
photo details (bottom):
Canon MP-E 65mm 1-5x lens on a Canon 6D
ISO 400, f/13, 1/160 sec
diffuse twin flash
More information about Stephanidae at the Tree of Life project.