Where did Shakespeare learn about scorpions?

I'm researching scorpions for a client and I suddenly rememembered a quote from Macbeth:  

“O, full of scorpions is my mind!” 

And  I thought--how did Shakespeare know about scorptions? They don't HAVE scorpions in England. Do they? (Yes, I know, he would have known about scorpions from the constellation Scorpio, but work with me here.) Turns out they did have scorpions in England. This from Wikipedia:

Scorpions are found on all major land masses except Antarctica. Scorpions did not occur naturally in Great Britain, New Zealand and some of the islands in Oceania, but have now been accidentally introduced in some of these places by human trade and commerce.

Who knew?