Traders standing at the corner of the map

While playing Dwarf Fortress (0.34.11), I noticed that a trader had come with my last migrant wave. Instead of following the rest of the dwarves to the fortress, he decided to hang around at the edge of the map. I didn't pay much attention to that at first, but now there are suddenly five traders having some sort of meeting there.

I can find them in the Others tab of the unit screen, so they were not real migrants, but I'm clueless as to what I should do with them.

Here's an image of the little Trader club:

Do they have some sort of purpose?

EDIT: I should have made this clearer, but I'm aware of how to trade with caravans. However, these traders are seemingly not associated with any caravans.

Solution 1:

Those traders are present due to a bug, and the issue should be resolved in a newer version (whenever Toady gets around to fixing it).

In the mean time, consider them useful scouts and decoys in the ongoing Goblin conflict.