For clarity, the encounter is 1d8+2 stirge, and they rolled an 8.
Ouch.
No, my players have also developed a healthy fear of these little buggers. I think my party was a little higher level than yours at their first encounter with them, because I did not have any compunction about swarming as many as eight on a single target (and that was generous, as tiny creatures they aren't limited to one body per "square," and generally dropped two or three PCs per encounter. I avoided ignominious PC death by having the stirges disengage upon unconsciousness, as you did -- in general I think it is logical they would defend themselves first and feast later.
Now the running joke of the group is whether something is "stronger or weaker than a mosquito attack".
Stirges are the size of cats. Their probosces are not unlike stilettos slaked with an anticoagulant. Mosquitos they are not.
I wouldn' t have allowed stirges again so soon. Repetitive encounters can be quite boring.
Or indicative of an ecology. You'll forgive me for saying so, TC, but labeling two encounters with the same monster in three days 'boring' is a bit heavy handed.
I don't think you did anything wrong (although I think a maximum of two stirges per person is an awful generous ruling, I believe Basic and 1e specified that stirges generally spread out amongst available targets fairly evenly, and I still keep to either that rule of thumb or "random targeting on!" methods of stirge allocation).
That's kind of you. My stirges understand the benefits of a swarm are quickly lost when spread out over more than one or two targets.
It's good to have some basic monsters to inspire true fear in adventurers. Stirges, green slime, rust monsters still all seem to have it where things like medusas, wights, and wraiths have had their teeth pulled.
This is why I'm really posting.
I think many of us who have been doing this forever have become jaded. I'm running a table for eight folks who are either brand new to the game with D&D5 or who haven't played for 20+ years, and it is /hard/ for me to reconcile my own impressions of the game with theirs. I look at the wraith and I agree with you -- life drain healing on a long rest? What is that about? -- but defanged or not, the experience scared the /bejeezus/ out of these guys. They ran like the dickens, and only came back to fight the wraith in Wave Echo after a boatload of prep and planning.
I am trying /so hard/ not to enforce my perceptions on this group and their adventures, because an encounter that seems like a throwaway cakewalk to me will be the subject of hushed and cautious whispers three weeks later.
The more I play with these guys the more convinced I become that it's not the game that's broken -- it's us.