Wasps love Sugar!

Often people will leave old Cola or other soft drink cans outside or in the bin. If just one wasp gets a taste of just one item, it will encourage other scavenger wasps to join it. This can end up with more than a dozen hanging around one bin!

Jam and other sugary substances are prime for encouraging wasps to hang around.

To avoid this... put sugary items in a bag in the bin. If they hang around the bin, try moving it; they navigate via recognition. If you change the location of the bin, they may well lose interest in it... but I do not guarantee this.