Darkling Beetle

Darkling beetles are a huge family of beetles found almost everywhere on Earth, from deserts to forests to kitchen cupboards. They belong to the family Tenebrionidae, which has around 20,000 known species. The best-known darkling beetle is the mealworm beetle, whose larvae, mealworms, are sold as food for pets.

Darkling beetle Quick Facts

Common name	Darkling beetle
Scientific name	Tenebrionidae
Kingdom	Animalia
Phylum	Arthropoda
Class	Insecta
Order	Coleoptera
Type	Insect (beetle family)
Diet	Decaying plants, fungi, seeds, grain, dead insects
Habitat	Deserts, grasslands, forests and stored grain
Native range	Worldwide except Antarctica
Size	About 2 mm to over 3 cm long
Colours	Mostly black or dark brown
Special feature	Larvae of the mealworm beetle are mealworms

Darkling beetles get their name from their usually dark colors and their habit of hiding in dark places during the day. Many species come out at night to feed.

Description

Darkling beetles come in many sizes, from about 2 mm to more than 3 cm long. Most are black or dark brown, often with a smooth or slightly bumpy shell. They have chewing mouthparts and antennae made of many small segments, often thickened toward the tip.

Like all beetles, darkling beetles have hard front wings called elytra that cover and protect the soft flying wings underneath. In many desert species, the elytra are fused together, so these beetles cannot fly at all. The sealed wing covers also help them hold in moisture. Other darkling beetles, including the mealworm beetle, can fly.

The adult mealworm beetle (Tenebrio molitor) is about 1.2 to 1.8 cm long and shiny black or dark brown.

Habitat

Darkling beetles live on every continent except Antarctica. They are especially common and varied in dry, desert regions, but they also live in grasslands, forests and farms. Some live in animal burrows, ant nests or caves.

During the day, most species hide in cool, dark places, such as under rocks, logs, leaf litter and loose bark. Some, like mealworm beetles and flour beetles, live in barns, mills, warehouses and kitchens where grain and flour are stored.

Diet

Most darkling beetles are scavengers that eat almost any kind of dead or decaying material. Their diet can include:

• Rotting wood and decaying leaves
• Fungi
• Seeds and grains, including stored flour and cereal
• Dead insects and animal droppings
• Living plants and seedlings (some species)

Many desert darkling beetles get almost all the water they need from their food. A few species in the Namib Desert in Africa have an amazing trick: on foggy mornings, they climb to the top of a sand dune and tilt their bodies into the wind. Tiny droplets of fog collect on their backs and roll down into their mouths.

Life Cycle

Darkling beetles go through complete metamorphosis, with four stages: egg, larva, pupa and adult. Here is the life cycle of the mealworm beetle:

• Egg: The female lays tiny, white, bean-shaped eggs in soil, flour or grain. Over her life she can lay a few hundred eggs, sometimes up to about 500. The eggs hatch in about 4 to 19 days, depending on the temperature.
• Larva (mealworm): The mealworm is long, shiny and yellow-brown, with a hard outer skin. It looks like a worm, but it has six tiny legs near its head. Mealworms eat a lot and molt (shed their skin) many times as they grow. This stage usually lasts a few months.
• Pupa: The larva turns into a pale, cream-colored pupa that does not eat and barely moves. After about 1 to 3 weeks, the adult beetle comes out.
• Adult: Newly emerged adults are pale but soon darken to black. Adult mealworm beetles usually live for a couple of months.

The whole cycle takes several months, often less than a year in warm conditions. Some larger desert darkling beetles can live much longer as adults, sometimes several years.

Behavior and Defense

Many darkling beetles defend themselves with smelly chemicals. Some North American desert darklings, called stink beetles or pinacate beetles, have a funny warning pose: when disturbed, they stick their back end up in the air, almost like doing a headstand. If the predator keeps bothering them, they release a foul-smelling spray.

Darkling beetles also have tough outer shells and often play dead when picked up.

Why Darkling Beetles Matter

Darkling beetles are important recyclers. By eating dead plants, fungi and other waste, they help break down material and return nutrients to the soil. They are also food for many birds, lizards, rodents and other animals.

Mealworms are raised in huge numbers as food for pet reptiles, birds and fish, and in some countries they are even eaten by people. Scientists have also discovered that mealworms can chew and digest some kinds of plastic, such as polystyrene foam, which may someday help with plastic waste.

As a Pest

Some darkling beetles are pests. Flour beetles and mealworms can infest stored flour, grain, cereal and pet food. The lesser mealworm is a common pest in poultry houses. In gardens, a few species chew on seedlings at ground level or nibble leaves and young fruit.

To keep darkling beetles out of stored food, keep flour and grain in airtight containers, clean up spills and throw away any infested food. In the garden, remove boards, piles of debris and weeds where the beetles hide, and protect seedlings with collars or row covers.

Darkling beetle FAQs