I have gotten bit by 3 different bugs that have all given me itchy bites but they are oh so different.
The most recent one is a tick bite, today is the first time I ever remember having a tick bite. I could not feel the tick at all until I felt my neck with my hand. It didn't suck much if any blood(how do I know? It looked deflated and alive after I grabbed it and pulled it off). It immediately started itching after I pulled the tick off but that itch is resolving. There is no swelling at the moment.
Mosquito bites are also from a blood sucking bug but this is way different. I actually once endured a full mosquito bite while awake at night. I can tell you from that experience, a mosquito bite is painless at first and then as it continues to suck blood it becomes painful, almost as though it injected venom. After the mosquito flies off nothing happens for several hours. But then it becomes irresistibly itchy(so I rub instead of scratch it) and is like that for a few hours at a time, several times a day.
Spider bites are even more different. Whether I am awake or asleep, the spider biting me is unnoticeable. Then a few hours later it is just like a mosquito bite but worse(again irresistibly itchy for a few hours at a time, several times a day but the itch is much worse.
So yeah, 3 bugs, all give itchy bites, but the bites are so different in timing and/or severity. No allergies to anything except pollen and pet dander. Why are they so different, especially the tick and mosquito which both suck on blood?