I found this little insect, which is less than two millimetres long, in a bag of walnuts imported from France. It's a psocid, commonly known as a booklouse, on account of the fact that these often turn up in the bindings of old books that have been stored in a damp place. They also like wallpaper and we used to find them behind peeling damp wallpaper in our house, before we stripped it all off and redecorated, thereby making scores of booklice homeless; I suspect they feed on wallpaper paste.
Psocids are also found on tree bark and are sometimes known as barklice.
Psocids look superficially like very small aphids but instead of a piecing feeding stylet they have biting jaws, that are visible in this side view.
Some species are wingless, others have wings that they fold over their backs like a tent, but this one only has vestigial wings - or perhaps they are wings that have yet to develop fully.
Other distinctive features are the relatively large compound eyes positioned on either side of the head and the long antennae.