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Beginners Guide to Beetle Description Part 1

Updated: Feb 20, 2021

The coleopteran highlighted in this week's blog post is believed to be a Dusty June Beetle (Amblonoxia palpalis). This specimen can be described as having an elongate oval body just under an inch long. This brown beetle has antennae with 8-10 segments with a lamellate shape. The beetle is covered in bristles (setose). The underside of the abdomen (sternum) has longer bristles, working their way up between the pronotum and the top of the abdomen. The top of the head, the exposed scutellum, and the elytra have very short hairs compared to the beetle's underside.

Fig. 1. This Dusty June Beetle is showing off its lamellate antennae. Photo by N. Morrison/MYOPScience

The legs have heavy spines on the femur and the tibia. The tarsal formula is 5 segments on the front tarsi, 5 segments on the second tarsi, and 4 segments on the third tarsi.

Fig. 2. The tarsal formula is displayed. Photo by N. Morrison/MYOPScience

To ID this beetle, I followed the taxonomic groups down to the species as follows:

  • 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 – Scarabaeidae

  • Subfamily Melolonthinae

  • Genus – Amblonoxia

  • Species – palpalis

It wasn't easy to get past the family. I struggled with choosing the family Pleocomidae or Scarabaeidae because both beetles have genus with hair. One factor that helped me choose Scarabaeidae was that this beetle has a shield-like structure (clypeus) above its mouthparts that closely resemble those from the Scarab family. I did not choose the Pleocomidae family because they tended to have a narrower and V-shaped clypeus above the mouthparts. I chose the subfamily Melolonthinae because of the beetle's elytra coloration, convex/elongate oval body shape, lamellate antennae, size, and its clypeus lacked resemblance to the clypeus of a dung beetle. Furthering my identification, I decided that this beetle was in the genus Amblonoxia due to the bristles' location, the color of its head and elytra, and the shape of the body. There were two species, one being fieldi and the other being palpalis. I chose Amblonoxia palpalis instead of Amblonoxia fieldi because this specimen has a darker brown color, longer bristle length on the sternum, and fewer bristles on the elytra. I struggled with the identification, but I am content with the classification. I am thrilled you followed along. Thank you.

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