Thompson and I worked on this a bit, and I think we've agreed it's just tiny, nasty mosquitoes the McGarrigles are complaining about. Sure is a great song. Here's a 1976 performance by the McGarrigles:

https://www.youtube.com/watch?v=TUr8MJYAjRk

There's a younger duo named "First Aid Kit" with a live performance of the song:

https://www.youtube.com/watch?v=oCD0oyDoFDw

And here's Kirsty MacColl:

https://www.youtube.com/watch?v=tmmelsbp96k