A perpetually happy Venezuelan Leptogenys
We don’t really know why some species of Leptogenys hunting ants sport a permanent grin. The oddly ecstatic mandible shape might, however, have something to do with handling the broadly curved exoskeleton of their preferred prey: isopods (the sow bugs and pill bugs).
Flickr user “venwu225” recently uploaded a fantastic series of the related species L. falcigera in action. Some of the shots show how the mandibles allow the ant to grip the isopod both above and below its wide skirt of armor. Cool stuff.
photo details: Canon MP-E 65mm 1-5x macro lens on a Canon 20D
ISO 100, f/13, 1/250 sec, flash diffused through tracing paper
Myrmecos Blog 
I see a heart shape there. Maybe she is saying to the isopod, “I love to eat you”.
Man those are scimitar like mandibles! But the action shots show they work quite well!
Nice pic.. Thanks for the link. From that I learn about the insect enthusiast groups there, so I rushed to upload my pics there.
Cheers.
Another shot right after the Flickr Leptogenys series shows Anoplolepis attacking a cockroach. While the leptos use those big mandibles to handle the body of the prey animal directly, the anoplos go for the legs. Seems there could be a different set of advantages or disadvantages to each method. Leptos have an additional advantage of having a long sting and powerful venom to immobilize their armored, but “clunky” prey, while the anoplos lack a sting and do well to immobilize prey by spread-eagling it before smearing formic acid on it.