Mealworm Beetle Tenebrio molitor
The Mealworm Beetle is a black beetle measuring 13 to 18 mm. Right after pupation the beetle is brown, but the colour changes into black in just a few hours. Like other darkling beetles it has a rather massive snout. There appear to be lines over the hind shields. The neck shield has two ditches near the edge. Other punctations, ditches or irregularities often appear as well, like the two deep pitches in the neck shield of our model.
Only 12 days after they have been being laid the eggs hatch. The larvae appear. They are slender, yellowish brown and do look like wire worms. They eat whole seeds, damaged seeds, meal etc. The larvae may live up to well over one year. Full grown larvae measure an amazing 50 mm! The larvae usually overwinter, when needed. Pupation however takes some two weeks only.
The reputation of the well known larva (the Mealworm) is weird. On the one hand they are a pest in stored grains and meal. Once infested they may destroy the contents of an entire storage room in just a short time. On the other hand they are being sold world wide as food for pets. They are fed to birds, fish, amphibians and reptiles, scorpions and some bigger insects as the Mantis. And in some countries they are considered as a delicatesse by man as well. Deep fried they are increasingly populair as a snack.
In the wild the larvae eat moulding wood and decaying seeds of grasses. Especially the House Sparrow uses grasses to build its nest. And Mealworms often appear once the nest is abandoned. The adult beetles then find their way into houses and storage rooms. However encountering just one adult beetle inside the house is no cause for alarm. It probably came straight out of a bird's nest.
The Mealworm Beetle is a species appearing all over the world. It is however more numerous in the moderate climate zone.