I recently returned from a stay in the south of France where I had more contact with mosquitos than I would have liked. During a visit to Arles I was beset with extreme itching of my left upper arm. It was as if a long needle had been inserted, with the difference that the result was itch rather than pain. This led me to wonder about the mechanisms resulting from a mosquito bite. The only bites on the part affected were at least two days old and had had no consequences of comparable intensity prior to that. I am familiar enough with the coming and going of the swelling due to mosquito bites collected in the garden at home. I have, however, never carefully observed the course of events or tried to find out what is known about how it works. On that day I decided that the time had come and that I should consult the internet and other sources. I had read that the mosquito injects some kind of anaesthetic but I knew no more than that. I was afraid that these phenomena, while so irritating, might have been considered of too little importance to be studied seriously.
Looking at what is on the internet and books I have at home provided some information but I did not find a comprehensive account to satisfy my curiosity. Some things I did find are as follows. Local allergic reactions are often associated with the production of immunoglobulins of type IgE and the activation of mast cells. The mast cells release substances contained in their granules and this causes an immediate reaction. Substances they produce later lead to the activation of white blood cells such as eosinophils and this may well be what causes a second phase of itching and swelling. Some questions remain. Is it an observational fact that a single bite leads to at most two phases of itching (and not three, for instance)? Perhaps I can do some field work on that point. If the mosquito saliva produces an allergic reaction when injected into to the blood why does it not, at least in the vast majority of cases, produce something really bad like an anaphylactic shock? Something I did not find anywhere is what the substances in the mosquito saliva are which lead to the itching. Presumably they affect certain nerves. I wonder if the mechanism of this is understood.