I have started using a script, closecomments.php, to block any comments on posts older than thirty days old. At least, if I run the script every day, that will be the case, and otherwise it may be 31 or 32 days.
I did this because I get comment spam and also trolls, and often they use one or two particular entries. I suppose that particular URL has been handed on.
There’s one entry I would have liked to leave open, and that is Macroglossum Stellatarum, which may come to life again when the moths return. I suppose there is no way of opening a single comment?