In which I pretend to be an archaeological entomologist

Shortly before Christmas, I was contacted by everyone's favorite gay archaeologist, Homer. He was working a dig in Tucson and had been uncovering artifacts from the 1890s. One of them was an old can that contained a bunch of dirt mixed with insects. If he sent me a sample, would I be willing to try to identify them? Ever up for a challenge, I said yes. A few days later, a vial of dirt mixed with insect parts arrived. I dug out some equipment and got to work.

Leg

The sample contained a bunch of fragments from what appeared to be a fairly large kind of beetle. From the size, color, and location, I had a pretty good idea right away what I was working with. The leg fragments (femora and tibiae only) were the first big clue. The tibia (straight, narrow section above) is about 6.5 mm long and the femur (the more oval secction) is about 7 mm long. They come from a pretty big bug. The metallic green coloring is distinctive. There were what looked like fragments of ribbon of the same color. These were sternites, the ridges of the abdominal segments.

Sternites

The sample also included a number of oddly shaped plate-like structures that were not metallic green. These were pronota. the pronotum is the dorsal covering of an insect's thorax.

Pronotum

By this point, I was pretty sure that I was working with parts of a biggish scarab beetle called a fig eater (Cotinis mutabilis) . They are bright green with a metallic luster below, and are green and brown with a matte luster above. I have several in my collection, including a couple collected right in Homer's back yard. When I compared the legs and pronota to those on my mounted specimens, they matched beautifully.

Cotinis mirabilis mutabilis
The pronotum is just towards the head from the pin

Cotinis mirabilis mutabilis showing the metallic green underside

Fig eaters range from Texas to California and south into Mexico. In the Tucson area they are a common species and fly from July to September during the summer monsoons. As their name implies, they eat fruit, especially if it's overripe or fermenting. I wonder if they had not entered the can to find fruit or fruit residues inside. Something was probably attracting them to the can, since I found so many remains. I recovered 18 pronota from the sample, which means that there were at least that many beetles in the can at one point.