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Beginners Guide to Beetle Description Part 2

I remember the first time I saw this beetle. It was a sunny day, and there were no clouds in sight. I was on a walk and saw what looked like any other darkling beetle (Family Tenebrionidae). In my area, the Head-Standing Darkling Beetles are very common. As I got closer, I realized it was not your typical darkling beetle because the body was far bumpier (nodulous) (Figure 1). The pronotum was wider near the head and tapered off into the abdomen. When I crouched down to the ground to get a better look, the beetle quickly tucked all of its appendages. It looked like a tiny black nodulous stone approximately an inch in length. The legs and the antennae seemed to blend into the rest of the body. The beetle was the Diabolical Ironclad Beetle (Phleodes diabolicus), a native to California. Phleodes diabolicus is the beetle under my digital microscope this week.

Fig. 1. The picture shows Phloeodes diabolicus and its bumpy texture. Photo by N.Morrison/MYOPS

The following is the taxonomic classification of Phleodes diabolicus:

  • Domain - Eukarya or a cell with a true nucleus

  • Kingdom - Animalia

  • Phylum - Arthropoda or an invertebrate with a segmented body and jointed limbs

  • Class - Insect

  • Order – Coleoptera or sheathed wings

  • Suborder – Polyphaga

  • Family – Tenebrionoidea (Darkling and Blister Beetles)

  • Genus – Phloeodes

  • Species – diabolicus

The Diabolical Ironclad beetle has bead-like antennae (moniliform) received by the antennal sclerite attached to the beetle's head. The head recesses into the concavity of the prothorax (amplected). The tarsal formula displayed is 5-5-4 (Figure 2). The front tarsi have five segments, the middle tarsi have five segments, and the hind tarsi has four segments.

Fig. 2. The picture shows the tarsi formula-5-5-4 and the bead-like antennae. Photo by N.Morrison/MYOPS

You will notice that the elytra lack a scutellum, the small triangle-shaped piece between the pronotum and the abdomen on closer inspection. You will also see the elytra suture, which hints at the beetle's lack of hind wings. The Diabolical Ironclad Beetle is a ground-dwelling beetle that has invested all of its energy into becoming impenetrable. The sutured elytra are very thick and are rumored to be tough enough to keep the beetle alive, even after being run over by a car. In addition to its toughness, it has small grooves for its antennae to fold into (antennal fossa) (Figure 3). The antennal fossa allows the beetle to fold all of its appendages tightly to avoid being broken off during blunt force trauma.

Fig. 3. The picture shows the antennal fossa on the underside of the beetle's head. Photo by N.Morrison/MYOPS

The Diabolical Ironclad Beetle has quickly become one of my new favorite beetles because of its timid nature, efficient use of its body plan, and durable anatomy. Thank you again for following along. Hopefully, you will join me for next week's part 3 in the series.

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