Forelius pruinosus Ants and Saguaro Cactus Fruit

Fallen Saguaro fruit and _Forelius pruinosus_ ants

One day in late June, 2003, I was walking through Saguaro National Park East. The Sagauro Cactus fruits were starting to ripen, and a few had fallen to the ground.

Looking at one of the fruits, I saw what looked like little red sparks walking on the fruits and heading away in a single-file line. What on earth?

I knelt down to look a little more closely.

Fallen Saguaro fruit and tiny _Forelius pruinosus_ ants, with my fingers for scale.

There were tiny ants - Forelius pruinosus - filing into the  opening on the end of the fallen fruit. The ants were gorging themselves on the sweet red juice inside.

Close-up of opening into Saguaro Fruit. You can see the red flesh inside the fruit, and the _Forelius pruinosus_ entering the opening.

Close-up of _Forelius pruinosus_ worker drinking juice from fallen Saguaro fruit.

They were eating so much of the juice that their gasters were swollen like over-filled water balloons with the bright red fruit juice. You could see the bright red fluid in their crops through the stretched membranes of their gasters.

_Forelius pruinosus_ workers on Saguaro Fruit. You can tell which one has filled up on the fruit juice - the membranes of that ant’s gaster are stretched so far that the armour plating of the ant’s sternites and tergites no longer overlap as they normally do.

I got a real kick out of seeing this. It was a little bit like watching bright-red animated Christmas lights walking along the desert floor.