Dark beetles (family Tenebrionidae) are a large and diverse beetle family with over 20,000 known species worldwide and over 1,500 species in North America. Many home gardeners who raise chickens or ducks are familiar with mealworms, the larval form of the black beetle, and may have even tried raising these nutrient-rich worms.
While a black beetle can be a nutritious treat for birds or a tasty bait for fish, it can also be problematic for gardeners. Some adults and larvae chew on seedlings and the lower leaves of plants. They leave traces of damage similar to those of cutworms or related pests, and attack leaves with their chewing mouthparts. Fortunately, more established plants over 5-6 inches typically aren't bothered by the dark beetle.
Among the thousands of species of darkling, there are several species such as the red flour beetle and the tangled flour beetle that attack stored grains. They can be pests in grocery stores and households, and are a major problem in grain elevators and other storage facilities. Fortunately, many problems with the black beetle can be solved through good gardening and hygiene.
Darkling Beetle overview
A black beetle belongs to the Tenebrionidae insect family. Source: Bernard Dupont
As the name suggests, adult black beetles are typically dark brown or black in color. They are sometimes confused with predatory ground beetles (Carabidae), but Tenebrionidae beetles generally have club antennae. However, both families of beetles tend to be most active at night and are often flightless.
Because there is so much diversity in this family of beetles, adults of different genera or subfamilies have different sizes and appearances. Most have an elongated oval shape with convex to flattened bodies. Their size ranges from 1-60mm worldwide with many species within 2.5-20mm in North America. However, according to the National Park Service, Tenebrionidae beetles found in the Grand Canyon can reach as much as 1.5 inches (~ 38 mm) in length!
As with other insect species, the black beetle's body is divided into a head, chest and stomach. For entomology enthusiasts out there, the unique differentiators of this family include marginalized eyes, distinct epistomal margin, heteromeric tarsi, closed prothoracic coxal cavities, clubbed or powerful antennae, and abdominal defensive gland reservoirs. This last property enables the beetles to expel a very foul smelling liquid as their chemical defense against predators.
Darkling Beetles life cycle
The black beetle goes through four stages of development: egg, larva, pupa and adult. Many types of darklings are only active in spring through autumn. Some adult beetles can lay eggs before the onset of winter and these eggs remain dormant until the following spring to hatch as beetle larvae.
Any female can lay hundreds of tiny white sticky eggs in her lifetime. The eggs hatch into light yellow or brown larvae, commonly known as mealworms or false wireworms. A mealworm can molt up to 20 times during the 8-10 weeks of its larval stage, gradually growing in size to reach 1.5 inches in length. After their last molt, the black beetle larvae become brittle and whitish pupae that take 1-3 weeks to mature into adult black beetle.
Common living spaces
Adults and larvae are found in the wild or near the surface of the soil. They seek shelter in weed-filled environments, leaf litter, under rocks or stones, or in rotting tree trunks. There are some specialized species that are adapted to life in caves or in dry dunes. Some specialize in housing other mammals and beetles. Rodents, termites, and birds can all involuntarily share their homes with these intruders.
Species like the red and confused flour beetle specialize in grain and are attracted to grain stores and chicken coops. They can also inhabit places where gardeners or grain producers lay out material to dry, such as sheaves of wheat before threshing. These beetles are particularly attracted to grains with a high moisture content.
Dark beetles do not usually infest people's homes. In fact, many people buy mealworms to grow at home and even start businesses that sell these worms. However, accidental visitors may be near the kitchen or pantry where there is a source of food for them. They tend to be attracted to dark, cool, and sheltered places.
What do dark beetles eat?
Both adult and larval forms typically feed on plant debris, dead insects, and decomposing plant material such as rotting wood. A few are minor agricultural pests, although seldom causing severe damage to plants when eaten, they can become a vector for disease transmission.
Because of the diversity of this beetle family, there are species that specialize in different food sources. In forests, for example, some black beetles are surface-eaters, grazing on bark, lichens, and mushrooms. In deserts and arid climates, they are capable scavengers, feeding on whatever they can find, including animal manure or carrion.
How to control dark beetles
The black beetles of the Isomira species are very round. Source: tree growth
While the damage they cause may not be too severe to begin with, darklings can be vectors of various diseases that can worsen damage to plants. Black beetle infestation can also cause problems when rearing poultry, as they can also be carriers of bird diseases and bacteria such as salmonella.
Organic or chemical control
Since insects like the black beetle are a good source of nutrients for other animals like wild birds, chickens, ducks, etc., it is not advisable to use chemical sprays to control them. On organic poultry farms, farmers can use pyrethrum-based insecticides to manage their populations.
Environmental control and prevention
Environmental control and prevention are the most effective techniques to control black beetle populations and keep them from settling in your home or garden. Remove weeds that can protect bugs and check for leaks in your grain store.
Seedlings are the most endangered plants in the garden. Regularly inspect your young plants for damage and look around the plants and soil to check the source of the damage. You may find black beetles or other insects like cutworms as culprits. You can add a floating row cover as an additional protective barrier.
If you have an infestation on hand, first remove the source of the infestation. Think about how you will store all of your grain and grain products, including pet food, bird seeds, and pantry items. Find all infected material and place it in a tightly closed container before discarding. You can also freeze the infected material for at least five days to kill the adults and eggs.
In addition, some black beetles and their larval forms are attracted to animal feces. Remove them all from your property so as not to accidentally create a breeding ground for them.
frequently asked Questions
Ecnolagia grandis is a species that tends to be brown in color. Source: m9rt1n
Q: Are black beetles harmful?
A: There are thousands of species of black beetle all over the world. Some species can harm young plants by chewing on the developing leaves. Some species also feed on grain and can be a pest in silos, chicken coops, or even around the house. While incapable of stinging or biting people, they can be a vector for both plant and avian diseases.
Q: Are black beetles invasive?
A: Black beetles are a common and diverse family of insects found around the world. There are both invasive and native species of black beetle. The U.S. Department of Agriculture has been working on projects to monitor their population and movement due to increased risk of invasive species from world trade.
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