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Yellow Mealworm/Darkling Beetle Tenebrio molitor

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The adult is the darkling beetle.

The mealworm is NOT a worm. It is the larval stage (grub) of the yellow mealworm beetle, also called the darkling beetle (Tenebrio molitor). Although the grub looks a bit like a worm, the mealworm has six small, jointed legs. Both the larva and the beetle are nocturnal (active at night), but they are also active during the day.

The mealworm is the larval stage of the darkling beetle.

Anatomy: The tiny, white, bean-shaped eggs are about 2 mm long by .9 mm wide. Larvae are dark yellow with brown bands; they are up to about 35 mm long, have a segmented body, six legs (towards the front of the body) and two antennae. The pupa is white/cream with a large head and a pointed tail (it darkens as it grows). Like all insects, this beetle has a hard exoskeleton, six jointed legs, two antennae, compound eyes, and a body divided into three parts (the head, thorax, and abdomen). The adult is from 12 to 25 mm long and is dark brown.

Life Cycle: The mealworm undergoes complete metamorphosis. The female darkling beetle lays hundreds of tiny, white, oval eggs, which hatch into tiny mealworms (the larval stage) - it takes from 4 to 19 days to hatch. Each mealworm eats a tremendous amount and grows a lot, molting (shedding its exoskeleton) many times as it grows. It then enters the pupal stage (they often over-winter in this stage; this stage lasts up to 9 months). The pupa does not eat and seems inactive, but it is transforming itself into an adult. After pupating, a white adult darkwing beetle emerges from the pupa (this stage lasts from 2-3 weeks up to 9 months, if the pupal stage over-winters) -- it soon turns brown and then almost black. The adult lives for a few months. The entire life cycle takes about a year.