A Cremastocheilas relative, Lissomelas flohri, Bates 1889

During the July Sabino Canyon Butterfly Count Doug Mullins found a beetle that he described as big, black, rectangular and flat. It seemed too big for any Cremastocheilus, and though I suspected Lissomelas, there was something missing in this description...

Sca Cet Cre: Lissomelas flohri Bates 1889

Now I finally got the beetle.What a strange guy! 24mm long, it  looks like a plastic toy model of a beetle, with all unnecessary detail omitted. Even mouth parts and antennae were hidden under a round plate that completely closed off the head before I teased it open

 This photo of  the type specimen curated at the British Natural History Museum was posted for me on flickr. Many thanks to the curators for their help!

Photo: Hillary B. Warner NHM

I couldn't find much about the biology of these beetles. By most accounts they hilltop here in Arizona after the first summer rains. Doug, the butterfly man, notes that  this one was on "Cynea" hilltop with a mating aggregation (I still need to find out what that means. Aren't field notes fun? He told me later that several of the beetles were seen in the tops of smallish trees on a ridge close to Windy Point on Catalina Highway).
A guest at Fred Skillman's Beetle Bash in early July mentioned that he watched Lissomelas cruising the road in front of the Madera Canyon Lodge that morning.
Charles O'Brien found a whole series of very fresh dead ones after watching them cruise the parking lot of Kitt Peak. These fresh ones had a big patch of velvet on their elytra. The total, traceless lack.of this feature  made me doubt my initial identification of Doug's beetle until Bill Warner checked the picture above.

CW O'Briens's specimen with velvty spot on the elytra

Biology of Cremastocheilini:
I have often watched our tiny local fire ants grab half inch-sized scarabs that tumble down after blundering into the wall at the porch-light. The giants have no chance against those Lilliputian armies. In that case it means certain death for the beetle.

Solenopsis xyloni (Southern Fire Ant) tackles a small aphodine Scarab

 Cremastocheilini - Anteater Scarab Beetles make use of their own of this ant behavior. In Arizona, they  fly after the first monsoon rains until they find a fitting ant hill (species specific association, I think). They drop like dead and the ants will come running to grab the easy "prey" and carry it into their nest. But these beetles are uniquely  protected.

They pull down the lid that covers their heads (including antennae and mouth parts) like a soldier in a tank in battle mode. Ants dismember their prey by pulling off the legs, but here they find few spines or texture to grab onto. No exposed membranes to place a paralyzing sting- the sclerites of these beetles are a tight-fitting armor. Some sacrifice of leg flexibilty is noticeable. Once in the nest, the pitted bodies of most species of Cremastocheilus seem to absorb the ant's odor while also producing pheromones of their own from Thoracic glands to pacify the hosts. The velvety patch on the elytra of Lossomelas may serve a similar purpose. Supposedly the adult Cremastocheilus feed on ants and their brood. They lay their eggs in the ant nest and the beetle larvae feed on decaying plant material that the ants have discarded at the nest entrance.
The position and reduced size of the mouth parts of Lissomelas flohri make me wonder whether this species feeds much at all as adult. Lissomelas has not been found in any ant nests and the biology of this mostly Mexican beetle is still largely unknown Scarabaeus 11/1980