Silverfish (Order Thysanura) are generally silver-dusted brown or gray insects with a tapering body resembling a sideways carrot with legs. They are known for their habit of infesting houses and eating wallpaper or bookbinding glue.
What a surprise to find silverfish in an ant nest.
The silverfish is the white insect in the center of the photo. As you can see, it is in the tunnel with the ants.
My best guess is that they are in the family Nicoletiidae, possibly in the genus Grassiella. If you know more, I'd love to hear about it.
A few silverfish are beauticians of the ant world. They approach the ants to groom and clean their outer surface. The silverfish probably also gets a share of the ants' meal as payment.
These were found under rocks with native fire ants, Solenopsis sp., which is one reason the photos aren't closer.
While I was taking photos of the silverfish, I also found a few beetles. More on that tomorrow.