I'm sure it's not their poison attack. I haven't died against Queen and King mirelurks in at least 100 levels, but today both a 3* Legendary Mirelurk King and Queen (on two different servers) created deathzones around them. I had to give up on the King, and The Queen even died in her own deathzone (I am also sure nobody else killed her). After her death the zone seemingly disappeared.

Both time it was in nuked areas of the bog, but in neither there was a Scorchbeast nearby or at any point that I could tell. The first was the King in the tracks of the Flooded Trainyard, the Queen was just north of the Glass Caverns.

Anybody else had a similar experience? If there's a pattern that's a problem.