Welcome and have fun with us here at Gameboomers, mary!
I think there is only one place to lose a beetle. When I jumped off the metal steps coming down from the mountainside (after doing the Cameron bugeyed slide down the rope), my black beetle with ornate setting fell off my pocket.
Do you think this is where you lost yours?
Also check the etched stone area by the dig site.
Also, you can't climb back to the excavation site through the ladder - you have to take another ride down the rope from above - the mountain top.
Hey, that might be where you lost it since, you have to jump down from the rock pile after climbing the ladder. To get back to the rock pile (done by the dynamite) - from the boat, go behind the ruins of a building (not the path to the twisty climb up the mountains to the etched stone), take that path and it will lead to the rock pile.