Darkling beetles are one of the most common members of the beetle community in the Columbia Basin.
One in four named insects is a beetle. Beetles have biting and chewing mouth parts and two pairs of wings, although many common shrub-steppe beetles are wingless. The first pair of wings are leathery or hard and are not used in flight. Beetles have four stages of development: egg, larvae, pupa, and adult. Beetles range in size from both the largest and very nearly the smallest insects in the world and occupy more different habitats and niches than any other class of insect. The bodies of beetles have three main parts: head, thorax, and abdomen. Did you know beetles have a better fossil record than many other insect groups do? Scientists have estimated the oldest fossilized beetles are 280 million years old.
What is a darkling beetle?
In the Mid-Columbia Basin, darkling beetles are one of the most common members of the beetle community. Mostly, they are dark colored and spend a good deal of time walking about on the ground. Darkling beetles feed on dead plants (detritus) but also will eat fresh plant material. They prefer walking to flying. Their tracks easily can be observed in sandy areas, especially in early morning before wind has blown the tracks away. Darkling beetles are active both at night and during the day.
About 20 species of darkling beetles live in the Mid-Columbia Basin. The most common species, Eleodes hispilabris, is about 3.5 centimeters long and black in color with ridges down its back. You can find these beetles in your yard and garden or scurrying between clumps of vegetation in sagebrush/bunchgrass.
How do darkling beetles defend themselves?
Many darkling beetles have a very interesting defense mechanism. If disturbed, they assume a head down and tail up position, and if handled roughly, they emit a dark-colored, foul-smelling fluid. This behavior is enough to discourage all but the most determined predators. The fluid washes off easily with water in case of contact with your hands. Coyotes, foxes, hawks, snakes, ravens, and crows often eat darkling beetles. The larger species have no other insect predator as adults.
Where do darkling beetles go in winter?
Most species of darkling beetles are active above ground from spring to late fall. With the onset of winter weather, some species seek shelter below ground in burrows of other animals and remain there until warmer weather returns in the spring. Other species of darkling beetles do not live through the winter as adults. They lay eggs in the soil during warm weather and die with the onset of freezing. Their eggs hatch into larvae when warm weather returns. These larvae live in the soil for up to two years before the adults emerge to eat and reproduce.
"Science is constructed of facts as a house is of stones. But a collection of facts is no more a science than a heap of stones is a house." Henri Poincare
Keep in mind this fact sheet is intended to be used only as background information to support your effort to encourage inquiry-based science, which parallels the way scientists uncover knowledge and solve problems.
Raise a flour beetle.
Here's how: Mealworms are the larval stage of the darkling flour beetle. Mealworm larvae are commonly sold in pet stores as food for other animals (such as birds, lizards, snakes, and hedgehogs). Use a plastic shoe box or a food keeper with a tight-fitting lid. Cut ventilation holes in the lid, and cover these with fine mesh screen (fasten with a glue gun). Put a 2-centimeter layer of clean soil in the bottom of the container, and cover the soil with a 2-centimeter mixture of crushed cornflakes, cornmeal, three or four 1-centimeter-thick slices of potato or squash, used birdseed, and/or wheat bran/chaff. Shredded newspaper or wood chips can be sprinkled on top, giving the beetles a place to breed and hide. Mealworms feed on dry grains and need very little water to survive.
Identify the stages of the life-cycle of the beetle.
Here's how: Time the different stages of development. Conduct an adult population survey of the beetle farm and graph it over time. The adult beetles can be fed to pets just as the mealworms are. The adults also can be released into the environment. They will not become pests unless considerable numbers are released at one time.
Where are they going?
Take a trip outdoors to a sagebrush/bunchgrass community and find some darkling beetles scurrying about. Do not disturb them. Observe them in their random travel.
Questions a scientist might ask: How much time does a darkling beetle spend feeding, resting, and moving? Where do they go to feed? What are they doing when they feed? What are they eating? Where do they rest? If you find an extremely large population of darkling beetles, report it to the U.S. Fish and Wildlife Service.
Start a business.
Here's how: Expand your mealworm farm and start a business. Sell mealworms as pet food to private pet owners, pet shops, schools, and universities. Build a Web Page advertising your product. Develop your own recyclable package for mailing mealworms to customers. Apply for and receive a private business license. Keep records of sales and production. Use the Internet to communicate with private mealworm farmers nationwide.
- How to Know the Beetles, Arnett, 1980. W.C. Broan Company, New York.
- Peterson Field Guides: Insects, D. Borror and R. White, 1970. Houghton Mifflin Company, New York.
- Great Explorations in Math and Science (GEMS), Lawrence Hall of Science, University of California, Berkeley, California, Animals in Action (5-9), Terrarium Habitats (K-6), and Animal Defenses (Pre-K).
- The Private Eye, K. Ruef, 1992. The Private Eye Project, Seattle, Washington.
- Enchanted Learning - http://www.enchantedlearning.com/subjects/
- Teachers Corner - http://www.teachersnetwork.org/dcs/critter/mealworm
- Darlking Beetle/Mealworm Information - http://insected.arizona.edu/mealinfo.htm
- Coleopterists Society - http://www.coleopsoc.org/
- Tree of Life Web Project Coleoptera - http://tolweb.org/tree?group=Coleoptera&contgroup
Initial development and printing of this fact sheet was funded by an Eisenhower Grant to the Partnership for Arid Lands Stewardship. Written by Marilyn Fike; Series Editor: Georganne O'Connor; Design: WinSome Design; Printing: Eagle Printing and Graphic Design; First Printing: December 1997; Web Development: WinSome Design.