[4] Commonly mistaken with the black mealworm beetle (T. obscurus), key variations in regard to size and shape distinguish these two.

[5] Mealworms most-likely originated in the Mediterranean region, but are now present in many areas of the world as a result of human trade and colonization.

Records from the British Isles and northern Europe are from a later date, and mealworms are conspicuously absent from archaeological finds from ancient Egypt.

Larvae from the older beetles also show a rapid weight increase at an earlier age than those from young parents.

The reduction of male signaling capability may be due to increased expression of homozygous deleterious recessive alleles, caused by inbreeding.

One explanation provided by researchers for this findings is that noninfected males who are larger may allow females to gain genetic or material benefits.

[12] Evidence suggests that in many animal species, secondary sexual traits reflect male immunocompetence, the ability of an individual’s immune system to resist and control pathogens or parasites.

A study found that a single parasite-like immunological challenge, created via a nylon monofilament implant in the beetle, significantly reduced the sexual attractiveness and locomotor activity of males, it did not negatively affect their survival.

[14] When receiving constant food, male initial body mass had no correlations with phenoloxidase activity or encapsulation rate.

This shows that pheromone mediated attractiveness and the immunocompetence in terms of phenoloxidase activity of males were condition-dependent, as both decreased with nutritional stress.

molitor can be the host of many different pathogens and parasites, including entomopathogenic microbes, protozoa, and tapeworms, which can decrease the mealworm beetle’s survival or reproductive success.

[15] When the mealworms feed on infected rodent feces, they may consume the eggs of the tapeworm parasite Hymenolepis diminuta.

This also reduces the probability of the females being infected by their mates, and may cause them to pass on an enhanced level of immunocompetence to their offspring.

[15] Another way mealworms may display behavioral immunity is how they may tolerate infections by limiting negative effects on their reproductive success.

Cuticular color is dependent on melanin production, which requires phenoloxidase, an enzyme that is present in its inactive form inside haemocytes.

This shows why darker insects have a heightened immune response and are more resistant to pathogens that invade the hemocoel via the cuticle.

However, there was no significant difference in haemolymph antibacterial activity between black and tan lines, explained by how antimicrobial peptides are produced by haemocytes but are not involved in cuticular darkening.

[16] In T. molitor, the degree of cuticular melanization is a strong indicator of resistance to the entomopathogenic fungus Metarhizium anisopliae, which could be explained by the thicker and less porous cuticle displayed by darker insects compared to lighter ones.

This causes enhanced hemocyte circulation and antibacterial activity in the hemolymph, which likely maximizes resistance against bacterial infection.

[15] A study found that the effects of nutritional imbalance on body composition were buffered by the subsequent selection of complementary foods.

They found that self-selecting T. molitor beetles recovered from carbohydrate or protein deficiency within six days by selecting the complementary diet.

Specifically, the bacterium Exiguobacterium species, which was isolated from the midgut of mealworms, was demonstrated to degrade polystyrene in vitro.

Commercial growers incorporate a juvenile hormone into the feeding process to keep the mealworm in the larval stage and achieve an abnormal length of 2 cm or greater.

[21] Due to their high protein and fat content, as well as consuming large amounts of fiber, they represent a good food source for humans.

[26] Mealworm larvae contain levels of potassium, copper, sodium, selenium, iron and zinc that rival those of beef.

[26][27] Mealworms may be easily reared on fresh oats, wheat bran or grain, with sliced potato, carrots, or apple as a moisture source.

The small amount of space required to raise mealworms has made them relevant for scalable industrialized mass production.

[28] Some evidence suggests that T. molitor may pose a health risk, as humans and animals can consume the eggs and larvae of the beetle with grain-based food.

The first cases of T. molitor larvae in human organs date back to the 19th century, where their presence was observed in the gastrointestinal tract, including the stomach and intestines.