We describe a category of Feynman graphs and show how it relates to compact
symmetric multicategories (coloured modular operads) just as linear orders
relate to categories and rooted trees relate to multicategories. More
specifically we obtain the following nerve theorem: compact symmetric
multicategories can be characterised as presheaves on the category of Feynman
graphs subject to a Segal condition. This text is a write-up of the
second-named author's QPL6 talk; a more detailed account of this material will
appear elsewhere.