Why Do Moths Have Dust on Their Wings?

Updated April 17, 2017

Moths are insects that are related to butterflies. Both butterflies and moths belong to the insect order, Lepidoptera. According to the Arizona Desert Museum, more than 142,000 species of moths exist worldwide. Out of this number, more than 12,000 species, divided into 65 families occur in North America. Moths have their own unique features, including a dust-like substance all over their wings.

Moths undergo a complete metamorphosis. This means that they go through four stages in the course of their life cycle. The first stage is the egg stage, followed by the larval stage, the pupal stage and then the adult stage. Moths look different and have different needs at the various stages in their life cycle. They do not develop wings until they reach the final stage, when they turn into winged adults. It is the adult moths that have powdery wings.

Moth Wings

Both moth and butterfly wings are composed of thin layers of a protein called chitin. Moth wings have modified hairs known as scales that hold the wings together. These scales are so small that their true form can only be observed under a magnifying glass. Upon closer observation, the scales resemble interlocking tiles that serve to hold the delicate wings in place. These scales also come in different colours and give the different species of moths their unique markings and colourings. The scales are the "dust" that come off when someone touches the wings of a moth.

Eggs and Caterpillars

Moths lay their eggs on some plant species that their larvae or caterpillars will eat, when they emerge from the cocoon. They also lay their eggs in other places, such as on wool clothing, rugs and inside stored grain, for example, maize. When the larvae emerge from the eggs, they burrow into the maize and feed from it. Some plant species that moths favour -- like the tobacco plant -- have evolved to develop toxins and other defences like resinous secretions to deter caterpillars. However, moth caterpillars have also adapted to survive such defences by developing systems where they secrete the toxins from their system immediately after consuming the toxic leaves. They also eat only emerging sprouts, avoiding older leaves that have more toxins.

The Pupa

The next to final stage in the life cycle of a moth is the development of a hard outer shell known as a chrysalis. This is the pupal stage when the moth undergoes the final metamorphosis into an adult with wings. Apart from the chrysalis, moths also spin a cocoon to further protect themselves while they undergo metamorphosis. Up until the time of metamorphosis, the moth is a terrestrial insect. By the time the moth emerges from the cocoon, the metamorphosis is complete and the moth is an adult that can fly.

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