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Beginner Beetle Description Series Part 4

My Fiancée's uncle from Williams, California, provided me a second specimen for this week's blog. He was excited to bring me the new beetle that he found that he carefully placed in a cup and covered in cling wrap. He found the beetle on the farm where he works. When I first looked at the beetle, I thought it was unremarkable. I was wrong. It was a small black beetle that was approximately a centimeter in length and about 5 millimeters in width. The oblong-shaped beetle had a black scooped head half the pronotum's size, a black rounded pronotum equal in width to the abdomen, and elytra that were a very dark shade of brown (almost black). Its prosternum had more bristles (setae) than the rest of its body. It also had lightly setose elytra, a majority of its ventral covered in setae, as well as the typical setae between the joints to block intruders from entering the exoskeleton (Figure 1). It was a scarab beetle in California! I was astounded because I had never heard or seen any dung beetles in this state.

Fig. 1. The picture shows Onthophagus taurus and its defined features. Photo by N.Morrison/MYOPS

I had a tough time identifying this beetle as it was not a native to California. What made it so hard to identify was that there were no known dung beetles that I was aware of in California. This was clearly a dung beetle due to its scooped head, leg structures, tarsi segmentation, and antennae. So, I decided to look up non-native dung beetles in California, and that is when I found an article that pointed me to the correct identification of this beetle. It turned out to be the Taurus Scarab Beetle (Onthophagus taurus). The Taurus Scarab Beetle is native to Portugal East, China, and North Africa, among others. It is believed that the beetle was intentionally released recently in California to break down sheep and cow dung on farms (https://www.ukbeetles.co.uk/onthophagus-taurus).


The following is the taxonomic classification of Onthophagus taurus:

  • 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 (sternite not divided by coxa)

  • Family – Scarabaeidae

  • Genus – Onthophagus

  • Species – taurus

Additionally, the beetle did not have a visible scutellum. It did, however, have a shield-like structure (clypeus) above its mouthpart's, elbowed antennae (geniculate) with club (clavate) shaped antennomeres that are representative of the Scarab family (Figure 2).

Fig. 2. The picture shows the geniculate and clavate antennae. Photo by N.Morrison/MYOPS

Since it is part of the scarab family, we can also expect it to have the Tarsal formula of 5-5-5 (Figure 3). That means five segments in the feet (tarsi) in the front, hind, and rear. Although it does have this tarsal formula, the front tarsomeres are hidden within the scalloped leg.

Fig. 3. The picture shows the beetle's tarsal formula 5-5-5, which is characteristic of the Scarab family. Photo by N.Morrison/MYOPS

This non-native to California appears around April to July to mate. The males display extreme sexual dimorphism where they use their bull-like horns to fight other males as a mating ritual. The horns look super cool. The specimen we have is female based on its lack of horns on the front of its head. When the pair successfully mate, they build a den underneath a pile of dung where they can raise their offspring. Thank you again for following along with my blog. I much appreciate you following along. Hope to see you here next week. Don't be afraid to comment and hit the like button.

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