Don't do anything rash ... but Taylor Momsen just shared some intense pics of a poisonous spider bite that left her in the hospital.

Check out the pics ... you can see a fiery red splotch spreading from the bite, taking over a big chunk of her shin.

Last night, Taylor wrote, "Hospital today, show tomorrow, poisonous spiders are NO BUENO 🕷️🕷️but the show must go on, see you tomorrow Mexico City!"

She followed up with an update Wednesday morning, writing, "Or I just spend the night in the hospital…thank you to the amazing doctors who, well, they know."

The singer and former actress has incredibly bad luck with this sort of thing ... she was bitten by a bat mid-concert 2 years ago! 

Taylor made light of the awful coincidence, writing, “Add it to the list! Spider woman? Batgirl?”

After the 2024 bat bite in Spain, Taylor said she had to get rabies shots for 2 weeks ... hopefully this recovery is a lot more speedy!