Unidentified Beetle Pupa Found Near River Bank

Observation by Charles Prince:

First time seeing these and we would like to find out what they are. They found these under a sheet of plywood near their camp by the beach.

Jessie Moan, Forest Health Technician with the UAF Cooperative Extension, writes:

This is some kind of beetle pupa (the lifestage between a larva and an adult). Pupae are generally a non-mobile, non-feeding lifestage and are really interesting because the insect is undergoing massive changes in body structures, etc. between the immature and adult forms. It's a pretty cool find! 9/13/2018

Comments from LEO Editors:

There are approximately 57 beetle species in Alaska. Beetles go through four life stages: egg, larval, pupal, and adult. Beetle eggs take anywhere from 7 to 10 days to hatch in to a larva. During the larval stage, beetles begin to eat, and grow for approximately three months. After the larva has grown, its skin begins to harden and it transitions in to a pupa. Beetles remain in pupal stage for another 7 to 10 days, before reaching its adult stage. Erica Lujan Source: Arizona State University- Beetle Life Cycles, -Insect Identification - Beetles of Alaska