Sherbrooke, Wade C.
Southwestern Research Station
American Museum of Natural History
Portal, Arizona USA
Kimball, Bruce A
Monell Chemical Senses Center
Philadelphia, Pennsylvania USA
Horned lizards are largely myrmecophagus and successfully squirt systemic blood defensively at certain
mammalian predators that react with revulsion. We used bioassay-guided fractionation of blood plasma
with coyotes and mice in attempting to identify the active compound(s). Plasma was from blood-squirting
(P. cornutum and P. solare) and “non-blood squirting” (P. platyrhinos and P. modestum) species,
sometimes on and off from Pogonomyrmex diets. We believe that access to this widespread seed-
harvester ant diet, largely avoided by vertebrates due to their very potent vertebrate-selective toxin stings,
only became available to stem horned lizards with their evolution of unique prey capture techniques.
These involved visually tracking for extremely fast micro-second adjusted tongue capture specifically
directed at the ant’s thorax, avoiding the jaw-biting head or stinging abdomen of these dangerous ants.
These captures are coupled with rapid buccal passage, lacking mastication, but enhanced in subjugation of
ant defenses by application of massive mucus coatings — from tongue and other tissues — that continue
to the stomach. This uniquely broadened diet, with its antipredator defensive compound(s) acquired, led
to expanded opportunities and the diversification of the genus as its radiating clades spread across much
of arid North America.