Bombardier Beetle
Brachinus sp.
Observed along Madera Creek in Madera Canyon, Sta. Rita Mountains, Sta. Cruz Co., Arizona, USA. Sept 2010.
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That black and red coloration provides just a slight hint of the amazing defense possessed by these insects. Upon being disturbed or threatened two batches of biochemicals are ejected from the abdomen that then mix and literally explode. An audible popping sound and sometimes visible vapour from rapidly heated water is the result. Tapping a beetle lightly under a finger is sufficient to elicit this behavior. They hunt and scavenge along the muddy banks of riparian streams at night then retreat under debris or rocks by day.
Several species could be found in Arizona. The immature stage is an aquatic, larva (grub) that inhabits the flowing waters and there parasitizes the pupae of other types of aquatic beetles.