I have a security webcam set up to send me an email of the image when there is movement in its field of view.
A spider decided the camera lens (maybe the IR light was the attraction) was a nice place to do a dance. So… I started getting extremely frequent emails which had large attachments. This filled up the email box on my server and blocked incoming emails from people.
Denial of service by a spider.
It could have been worse. Do you remember my story about denial of service by a dust bunny?