How would you react if you saw one of these?
You can't tell from the photo, but this insect is roughly an inch-and-a-half long.
No need to be alarmed, however. That is not a stinger pointing out of it's body, but the wasp's extra-long abdomen.
Unless my recollections are wrong, it is a male ichneumonid wasp of the genus Megarhyssa.
In any case, no cause for alarm.
Note: This particular wasp emerged from a pile of firewood. The larvae feed on grubs within the wood.