Community Science: Japanese Beetle Survey

Community Science: Japanese Beetle Survey

Many of you might have seen pretty, shiny brown and metallic beetles in yards and parks, feeding in numbers on roses, Virginia creeper, or almost any other plant you can think of. These are Japanese beetles (Popillia japonica), a species of scarab beetle accidentally introduced to the eastern United States over 100 years ago. In the early 1990s, they arrived in the Denver area and for the last few years became a serious pest of ornamental plants and lawns. The adult beetles feed on hundreds of species of plants, preferring roses and vines. The larvae feed on the roots of well-watered lawn.

The Museum is trying to determine how far the Japanese beetle has spread in Colorado and to compile a distribution map of all the records we can obtain. For this, we sought your help in the previous two years and received hundreds of samples delivered by many citizen scientists of all ages. This year we are preparing a report to be published in a scientific journal.

How to identify a Japanese Beetle

All beetles look the same, right? Not quite so. The Japanese beetle is about 3/8” (8‒11 mm) long with brownish/copper-colored wing cases and green metallic front part. Below the wing cases is a row of white dots on each side. If you've found a small insect with these characteristics, you've found a Japanese beetle.

How you can help

The year 2017 was amazing: 215 citizen scientists brought in 2,235 specimens from Boulder to Pueblo, enabling us to produce a comprehensive distribution map of the beetle for the Denver metro area, which was published by the Denver Post in 2018. In 2018 and 2019, we wanted to see if the beetles invaded areas that were not affected the year before: western Lakewood, Wheat Ridge, Arvada, Commerce City, Thornton, and Broomfield to Loveland. While those areas were much less affected than central and southern Denver Metro, we received several records from citizen scientists. The Japanese beetle is spreading its wings and is likely to invade suburban areas previously unaffected. If you encounter Japanese beetles in areas not represented in the map below, please collect a few and preserve them in a well-sealed vial or bag. The preferred storage is in 70% rubbing alcohol in a tight container.  Attach a note with the following information:

  • the location (address) where the beetles were found;
  • when they were collected; and
  • who collected them.

Thank you again for your invaluable help! This is a project that could not be done without your support.

We will update the online distribution map and our online database with your records soon after I received them.



Krell, F-T. 2018. Japanese beetles make Colorado home. YourHub (Denver Post) July 12, 2018: 6T+9T.


Frank-Thorsten Krell, PhD

Senior Curator of Entomology

Back To Top