Like one of those 24 hour bugs? (9)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

Cryptic.  ‘Ephemera’ is a fever that lasts only a day. Certain insects such as the mayfly are sometimes termed ‘ephemera’ because of their very short life-span (typically 24 hours) and I guess some people might class them as bugs.