Blue Death-Feigning Beetle

The blue death-feigning beetle, also called the desert ironclad beetle, is a darkling beetle native to the southwestern United States, from southern California to Utah and New Mexico, and northwestern Mexico. It lives in dry, sandy habitats such as the Sonoran and Mojave Deserts and is highly adapted to heat. Adults reach about 18 to 21 mm and are most active at dawn and dusk. The beetle is omnivorous, eating dead insects, fruits, lichen and other plant matter. When threatened it feigns death, and its powdery blue color comes from a wax coating that prevents moisture loss.

About the blue death-feigning beetle

The blue death-feigning beetle, also called the desert ironclad beetle, is a small darkling beetle of the family Tenebrionidae, the same family as the mealworm beetle. It lives in the dry, sandy deserts of the southwestern United States and northwestern Mexico. Its name comes from its habit of playing dead when threatened.

The species was described in 1851 by LeConte, and its scientific name is Asbolus verrucosus. The species name verrucosus means "warty," a reference to the characteristic bumps on the beetle's hard wing covers, or elytra.

An adult is about 18 to 21 mm (0.71 to 0.83 in) long. Its most eye-catching feature is its color, a soft, powdery blue. That hue is due to a coating of wax on the body, which also helps keep the beetle from losing moisture in the desert heat.

Males and females are similar. Males are slightly smaller than females and have bristly red hairs on their antennae.

Darkling beetles make up a huge family of more than 20,000 species found around the world. The name comes from the Latin Tenebrio, chosen by Carl Linnaeus and meaning "lover of darkness," and many species do live in dark places.

Members of the family share a few features. They have antennae with 11 segments, eyes notched by a ridge on the front of the head, and five segments on the front and middle feet but only four on the hind feet. Many of the larger species cannot fly.

Within that family, the blue death-feigning beetle belongs to the subfamily Pimeliinae. Other members of the darkling beetle family include the mealworm and superworm beetles, whose larvae are raised as feeder insects, and the pinacate or desert stink beetles of the genus Eleodes, which also live in southwestern North America.

Behavior and diet

The blue death-feigning beetle is crepuscular, most active around dawn and dusk. It is well adapted to hot, dry conditions, and its waxy coat helps it hold on to water.

It is an omnivore and a scavenger. In the wild it eats dead insects, fruit, lichen and other plant matter. This fits a broader family pattern: most darkling beetles are generalists that eat decaying leaves, rotting wood, fresh plants, dead insects and fungi.

Darkling beetles in general have slow metabolisms, and adults of most species live long lives compared to other insects, from about six months to two years. Many adult darkling beetles also carry chemical defenses that offer some protection from predators.

The beetle's best-known trick is death-feigning. When something threatens it, the beetle goes still and acts as if it were dead, hoping a predator will lose interest.

This behavior, called apparent death or thanatosis, is found across the animal kingdom, from insects and crustaceans to birds, mammals, reptiles, amphibians and fish. It is usually triggered by a predator's attack. Breeding experiments on beetles in general, not this species specifically, have shown that the length of time an individual plays dead is partly inherited, and that beetles which play dead for longer survive better when a predator is around. That suggests the behavior really does help them survive.

The larvae have their own version of the trick. A larva of this species may reflex-bleed while it plays dead, releasing body fluid called hemolymph. The fluid acts like glue, so sand and debris stick to the larva and partly cover it. That disguise helps it avoid desert predators.

The young of this beetle are larvae that later pupate before becoming adults. Darkling beetle larvae are known as mealworms or false wireworms. They usually live underground, have tough, hardened bodies and are active at night.

This species is known to be hard to breed and rear in captivity. Getting larvae to pupate takes careful control of humidity and heat. One research breeding effort that began in 2014 did not rear its first adult until 2018.

Range and habitat

The blue death-feigning beetle is native to the southwestern United States, from southern California to Utah and New Mexico, and to northwestern Mexico. It lives in dry, sandy habitats, including the Sonoran and Mojave Deserts.

It is closely tied to this environment. In captivity it does best in low humidity, mimicking its natural home, with a sandy floor and places to hide under. Darkling beetles in general mainly occupy deserts and forests, where they act as scavengers of plant material.

Conservation status

The blue death-feigning beetle has not been assessed for the IUCN Red List, so it has no global conservation status.

The species is becoming more and more popular in the pet trade because it is easy to care for, hardy and long-lived. Most captive beetles are caught in the wild, and breeding them is difficult. Captive beetles need little heating, a sandy floor and hiding spots. They cannot climb smooth plastic or glass. They do best on protein-rich food but accept a wide range, including vegetables, fruit, lichen, shrimp and dead insects.

The species has also been studied in the lab. In 2015 its complete mitochondrial genome was sequenced, the first fully assembled one for a darkling beetle in the subfamily Pimeliinae.

Other invertebrates with pages here include the emperor scorpion and the Madagascar hissing cockroach.