These aren’t only in dungeons, they are also found in the south cave AND lava cave! Trust me, I’ve seen them in there. The ones in caves usually want spoiled meat, but I’ve done passive tames and if it says, for example, (on a diplo) “feed azulberry to tame” you don’t have to. You can give it kibble instead. So I guess you can give dung beetles poo if they want spoiled meat. Raw meat also works to tame them. Oh, and have yourselves a good day with beetles! (Sorry it was long.)
They can destroy wooden structures. I was in the east underwatercave for deep SEA loot and Had a 1x1 wooden House with a bed. I had No weapon and so a lvl 200 dungbeatle Killed me nearly, Destroyer my bed and my foundation not what i expected.
On the island, I think the easiest place to find them is in the lower south cave. Go in with a longneck or a shotgun, turn left at the first intersection, kill the boas and spiders I. The first chamber, near the end of it there’s usually 1-3 beetles. Tame, and carry back to base w/ Petra. Easy fertilizer.