Arizona Road Trip Jan-Feb 2018 Part 9
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Arizona Road Trip Jan-Feb 2018 Part 9
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    Miscellaneous Images Taken In This Beautiful Area During Jan & Feb Of 2017!  
Miscellaneous Images (2)

Be Careful When You Check Your Pitfall Traps!

This 4 inch centipede fell into a pitfall trap! I carefully released it.

Bombardier Beetle In Queen Creek (Boyce Thompson Arboretum State Park)

I saw my first bombardier beetle on a field trip to the San Gabriel River in my Entomology class at California State University at Los Angeles. The approximate date was in the early 1960s. Today (6 February 2018) I found another one in scenic Queen Creek at Boyce Thompson Arboretum State Park, Arizona. This is such a fascinating beetle that I decided to include it in my 2018 Arizona Road Trip. After making several minor explosions directed at me, I carefully released it back into the creek bed.

Queen Creek: Where I found bombardier beetle while searching for ants.

Bombardier beetles of the genus Brachinus, a member of the large ground beetle family (Carabidae). These small beetles are about 13 mm long (1/2 inch). They are fairly common in southern California, particularly near streams, lakes and marshy areas. The wing covers (elytra) are dark blue-brown with a contrasting reddish-orange head and prothorax. This image is from my original insect collection over 50 years ago (circa early 1960s).

The bombardier beetle (Brachinus) is an example of irreducible complexity that is often used by advocates of intelligent design in their arguements against natural selection. How could such a complex and potentially lethal mechanism for repelling predators be produced by natural selection? This suborder of beetles known as Adephaga secrete a number of chemicals for a variety of purposes, only one of which is defense. Bombardier beetles inject an explosive mixture of hydroquinone, hydrogen peroxide plus several potent catalysts into a reaction chamber in the abdomen. Catalase breaks down the hydrogen peroxide into water and oxygen gas. Peroxidase oxidizes hydroquinone into benzoquinone. The mixture of chemicals and enzymes volatilizes instantly upon contact with the air, generating a puff of "smoke" and an audible popping sound. This caustic flatulence is totally controlled by the beetle, otherwise it might accidentally blow up its rear end. The explosive discharge apparently discourages predators, either by chemical irritation, heat or repugnance. The temperature of the explosive mixture of gasses and fluids is over 100 degrees Celsius, the boiling point of water. This astonishing chemical defense mechanism is discussed by D.J. Aneshansley and T. Eisner (1969) in Science Vol. 165: 61-63.

MIT scientist Eric Arndt and his colleagues have discovered that the superheated mixture comes out of the combustion chamber in a series of pulses rather than a continuous spray. This prevents the beetle's body from overheating while still scalding its would-be predator. See: Arndt, E.M. et al. 2015. "Mechanistic Origins of Bombardier Beetle (Brachinini) Explosion-Induced Defensive Spray Pulsation." Science 348 (6234): 563-567.

Other arthropods also produce some of the same chemicals found in bombardier beetles. Like bombardier beetles, these chemicals are used for defense or make the animal distasteful to predators; however, the mechanisms are not as sophisticated as bombardier beetles. Starting with these simpler mechanisms, a plausible step-by-step microevolutionary pathway culminating in bombardier beetles can be constructed. In fact, Mark Isaak (2003) discusses this in his on-line article entitled: "Bombardier Beetles and the Argument of Design."

One Fifth Of All The 1.5 Million Living Species On Earth Are Beetles!

This is probably a more accurate representation of the number of described species of beetles compared with other animals, plants, algae and fungi. There are at least 350,000 described species. Considering all the undescribed species, the number may exceed 400,000!

  University of California Museum of Paleontology Evolution 101: Why So Many Beetles?