I've been bitten on my upper arm - it happened when I was outside in the garden and noticed the discomfort. It's like the size of a mozzie bite but there are two small red marks not one, it doesn't itch at all. It's now hard underneath and I've got a red patch around it about the diameter of a mandarin that is raised up about 10mm, it's not changing in size but WTF has bitten me?