What could this be made of?

They told me it was a wasp, bee or something like that, but when I noticed the redness started, it looked like a mosquito bite.

This happened not only to me, but also to my neighbor, but on my leg. It started in the same way, only it spread much more and blisters appeared.

At first they thought that a snake had bitten her, but it turned out not to be the case.

What should I do? Shall I immediately cut off my hand with an ax?