Little Menace

When the sun is up I hang upside down,
For hundreds of years I've plagued this town.

When darkness falls I come out of the night,
To take what I need, just a little bite.

You know I exist although I'm not seen,
Tiny red marks betray where I've been.

No need to fear, for my bite does not kill,
But that which it carries may make you ill.

You'll sleep longer and it's harder to wake,
You're hot and you're cold, you shiver and shake.

I'm not all that bad, I leave you alive,
It's this thing I carry you might not survive.

But what can I do, I need to feed,
What will you do when I start to breed?