This beautiful big wasp was clearly looking for a place to lay eggs. Bug Guide notes that females are 38 mm long, ovipositor 130 mm, antennae 24 mm. The ovipositor is something to behold when unfurled. I have seen that with the other Megarhyssa wasp, M. macrurus (which is a bigger wasp): https://pbase.com/laroseforest/image/114209686
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