Why do bug bites itch so much? What cause that?

Why do bug bites itch so much? What cause that?
I do not know for ALL bugs...
- but for mosquito's - that straw thing that comes out of their mouths?
It certainly is two straw things - the first goes contained by your skin and injects their saliva - this helps your blood not to clot within that spot -it is also the chemical reaction that make you itch!
They inject their saliva so the second straw like article can suck up the blood and get stored contained by their bellies with no problem.
Female mosquito's do not nurture on blood for food - the blood nourishes their eggs. A typical mosquito lives two weeks - roughly speaking the same time it take for the egg to go through the pulpa stage...
Hope this help!
WHEN THEY BITE THEY LEAVE A SO CALLED SALAVA THAT YOUR BODY REACTS TOO WHICH CAUSES IT TO ITCH
Some bugs introduce toxins, enzymes, blood anti-coagulants, proteins, saliva, poisons, etc. etc. etc. when they bite. Because the bug is so tiny and because the amount of the substances are so miniscule, for humans, the worst case scenario is normally a minor skin reaction such as an itch or a small bump or some other skin antipathy which often go un-noticed. Most bugs cannot even bite through human skin - which is why the majority of insects and bugs can be handled undamagingly. We're quite au fait with the usual unlikeable list of bugs resembling bees, flies, mosquitoes, etc. etc. because they all pack a hurtful bite, but for the majority of bugs on the planet, their buzz is worse than their bite.
you might have morgellons disease. google it.