What Do Mealworms Change Into?

The final stage in the life cycle of the mealworm (tenebrio molitor) begins with the emergence of the darkling beetle from the pupa. Mealworms are the familiar yellowish grubs commonly found in elementary school science classes. Their high protein content makes them a nutritious food source for reptiles and other exotic pets. Like the butterfly, the darkling beetle completes metamorphosis in four distinct life stages: egg, larva, pupa, and adult.

  1. Egg

    • The female darkling beetle lays up to 500 eggs, each one to two millimeters wide. The white, oval-shaped eggs hatch within 4 to 19 days. Cold temperatures can significantly delay hatching. From each fertilized egg emerges a tiny, soft white mealworm.

    Larva

    • The newly hatched mealworm's exoskeleton soon hardens and takes on a yellow tint. The grub propels its long, segmented body with six short legs located just behind the head. Mealworms have a voracious appetite and feed primarily on grains, making them an agricultural pest. Like all arthropods, mealworms grow through molting, or shedding their exoskeletons. After five to 10 molts, the mealworm reaches its full length of approximately 2 centimeters. With the final molt, the larva enters its pupal stage.

    Pupa

    • The pupa seems inactive, but within the hard outer shell the grub is transforming into an adult darkling beetle. The yellow-white pupa is conical in shape, with a distinct, blunt head and a tapered tail. The pupa stage typically lasts for two to three weeks, but the mealworm may pupate for up to nine months in cold weather.

    Adult

    • The darkling beetle that emerges from the pupa is initially white, but its color soon darkens to brown, and then black. The adult beetle is 1 to 2.5 centimeters long, has two antennae, compound eyes, wings, and a body divided into three segments. The darkling beetle lives in its adult phase for roughly 30 days, during which time it must mate and lay eggs. The entire life cycle runs its course in about a year.