It could be a flexible cuticle instead of a rigid exoskeleton. I was wondering about the size issue and saw that Chamax is only size 6 so the weight might be explained that way. Less gravity, less weight. Of course the things need some better respiratory system than crustaceans or arthropods, but maybe a supercharger system to supplement at least book lungs might work for short bursts in order to catch their prey.
The acid might help serve as a component of this supercharger system which could also explain why the things need something like that in the first place.
The beetle predators could have semi-rigid chitin layer that doesn't have to be heavy enough to support weight, just create a shield to prevent acid damage. It could be concentrated around the head and forequarters, with flexible, softer sections layered over the limbs. This would reduce weight and protect the areas most likely to get sprayed.
If the beetles triangulate and are a bushwacking type of predator that lunges out from the surrounding earth to attack the chamax as they tunnel through it maybe more protection can be found from the earth's composition itself. Does it have a high alkali content that neutralizes the majority of the acid effects?
The predator in that case might have stiff, sticky hairs that cover the areas not protected by the semi-hard shell so the high alkali soil cakes onto the body and acts as that "ablative" layer you were describing. The advantage here would be that the ablative protection would be repaired as the creature tunnels through the ground. No caloric expenditure. Reduced caloric expenditure means more energy for search and catch time.
Maybe a good weapon for capturing a chamax that would also help limit exposure to the unprotected (or less protected) areas of the predators would be a harpoon that the predator "fires" in a manner similar to a cone snail. Again, the chemicals within the creature could form an explosive mixture that propels the dart through the wall of the chamax tunnel so the predator doesn't have to expose so much of itself. The dart doesn't even have to be poisoned because the chamax will destroy itself.
Then the predators can continue following the tunnels and signals to the maternal's lair.
Just some thoughts.
The acid might help serve as a component of this supercharger system which could also explain why the things need something like that in the first place.
The beetle predators could have semi-rigid chitin layer that doesn't have to be heavy enough to support weight, just create a shield to prevent acid damage. It could be concentrated around the head and forequarters, with flexible, softer sections layered over the limbs. This would reduce weight and protect the areas most likely to get sprayed.
If the beetles triangulate and are a bushwacking type of predator that lunges out from the surrounding earth to attack the chamax as they tunnel through it maybe more protection can be found from the earth's composition itself. Does it have a high alkali content that neutralizes the majority of the acid effects?
The predator in that case might have stiff, sticky hairs that cover the areas not protected by the semi-hard shell so the high alkali soil cakes onto the body and acts as that "ablative" layer you were describing. The advantage here would be that the ablative protection would be repaired as the creature tunnels through the ground. No caloric expenditure. Reduced caloric expenditure means more energy for search and catch time.
Maybe a good weapon for capturing a chamax that would also help limit exposure to the unprotected (or less protected) areas of the predators would be a harpoon that the predator "fires" in a manner similar to a cone snail. Again, the chemicals within the creature could form an explosive mixture that propels the dart through the wall of the chamax tunnel so the predator doesn't have to expose so much of itself. The dart doesn't even have to be poisoned because the chamax will destroy itself.
Then the predators can continue following the tunnels and signals to the maternal's lair.
Just some thoughts.