Never. I repeat never use a melee weapon on this. It will just melt from the acid blood. You might aswell strip naked too when fighting them because even your flak can be melted by their acid in 1 hit.
DO NOT ENGAGE OR YOU WILL DIE! I was hunting araneos when this thing came out of nowhere and three shot me! All my dimorphs were literally devoured when I came back. It is like centipedes in real life but instead of killing you slowly with poison it kills you with bites quickly. Do not equip anything lower than Chitin or you will get one shot.