Mealworm Diagram



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Mealworms are the larvae of grain beetles Tenebriol molitor.

Complete Metamorphosis
The grain beetle has four stages in its life cycle or metamorphosis.
The four stags are egg, larva, pupa, adult.
These four stages indicate a complete metamorphosis.

Gradual Metamorphosis
Other insects have a three stage metamorphosis.
The three stages are egg, nymph, adult.
This three stage metamorphosis is called a gradual metamorphosis.

Direct Metamorphosis
The silverfish's life cycle is a direct metamorphosis.
in direct metamotphosis, the insect hatches out of its egg and looks like an adult of that insect only smaller.
It then grows to adult size.


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The tiny eggs of the grain beetle are white, oval shaped and about one to one and a half millimeters long.  Eggs are laid singly or in clusters during the spring.  Each female lays about 275 eggs.  They are covered with a sticky substance that causes them to become coated with foreign matter under favorable conditions.  The eggs hatch in one-two weeks (4 to 14 days).

The newly hatched larva are whitish in color, shading to a dark yellowish-brown with darker areas where their thirteen segments join.  This stage lasts about four to five months under favorable conditions but they may spend up to two years in this stage depending on the environment.  The larva (mealworms), emerge from the egg, and are capable of immediately eating.  As the larvae grows, they become too big for their hard skin.  Mealworms shed their skin or molt nine to twenty times, which allows them to grow larger.  When fully grown, mealworms are about two and a half centimeters long and three millimeters in diameter. Most larvae mature by fall and pupate in the spring.  Individual larvae may wander far from the food source to pupate.

Fully developed mealworms change into inactive pupa.  In the pupa stage, mealworms are changing to the adult beetle.  At first, pupae are whitish in color and slowly turn yellowish brown in colr.  pupae are inactive, but will react to being touched by flipping their hind segments back and forth.  the pupae are shorter and fatter than fully grown mealworms.  This stage lasts one to thre weeks (the pupal stage lasting 7 to 24 days).

When the adult beetle emerges from the pupae they are completely white., but turn brown and finalyy black.  The beetle's wings are vestigial, as they are not used in flight.   Their movements are restricted to running on their three pairs of legs.  Hops of 5-8 centimeters seem to be their limit.  Their life span is only a few months.   A single female beetle may lay up to five hundred eggs during her lifetime.


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