Why do insect bites itch even after the insect has gone away?

Helen - That's a very good question because I get bitten like anything when I go researching in the tropics. It's all about what it leaves behind inside you. They actually pump saliva into you full of anti-coagulating compounds because they don't want your blood to clot while they're there trying to suck it up. They pump you full of anti-coagulants and leeches do the same. This is why you bleed a lot if you've had a leech bite. Your body can have an auto-immune response to that which is why it can swell. You can get used to it if you have a few over a few days. Some people can get used to it like having shots against allergies.