Moth-er Day

What the day is

Moth-er Day is observed on March 14. The pun is the whole premise, and the insect deserves the attention more than the joke does.

Origin and background

Moths vastly outnumber butterflies. There are roughly ten times as many moth species, and the distinction between the two is not a formal biological division at all: butterflies are a subgroup within the moths, so every butterfly is technically a moth that diverged. The familiar rules of thumb, antennae shape and resting wing position, are useful in practice and fail often enough to be unreliable.

The flame question was open for a long time. The common explanation held that moths navigate by the moon and mistake lamps for it, steering at a fixed angle and spiraling in. High-speed filming of insects around lights, published recently, supported a different account: flying insects turn their backs toward the brightest light, which is a sound instinct when the sky is the brightest thing above, and around an artificial light it tips them into banking, stalling and circling. They are not attracted so much as unable to orient.

That matters because artificial light at night is now recognized as a serious pressure on insect populations, alongside habitat loss and pesticides. Moths are significant nocturnal pollinators, and studies have found them visiting a wider range of plants than daytime pollinators in some settings, so their decline reaches well beyond the insects themselves.

The clothes moth, the one with the bad reputation, is a small minority. Only the larvae eat fabric, and only protein fibers such as wool and silk, which is why cotton is untouched in a wardrobe where a jumper has been destroyed.

How to take part

• Turn off outdoor lights, or fit warmer, shielded, downward-facing ones.
• Put a white sheet up with a light behind it and see what arrives.
• Plant night-scented flowers, which are moth-pollinated.
• Store wool clean and sealed. Larvae feed on the residue as much as the fiber.
• Look up the high-speed footage, which settles a very old question.