Russia has some scary new insects called “Vampire Moths” which are reported to suck blood for up to 20 minutes at a time. Although it isn’t much more harmful than being bitten by a handful of mosquitoes, scientists say that this might soon be a trait in other moths.
…they just haven’t yet evolved. Dum dum dum dum.
The scary part about this is that the blood-feeding is associated with the reproduction of the moths. The males are using the blood to give to salt-deficient females.
Give it enough time and I could easily see a book and movie deal about these little guys.