Moths

Moth caterpillars devour garden crops, but they aren’t all bad. In fact, they can also be important pollinators. Let’s see if we can sort out the Good Guys from the troublemakers.

Puppet the silkworm moth (Lottie) Public Domain

​As a child, I always thought that butterflies were colorful and flew in the daytime, while moths were fuzzy and flew only at night. Like everything else, it’s not that simple.

Lepidopterans, as moths and butterflies are called by scientists, are one of the easiest insect orders to recognize. Their name comes to us from Ancient Greek words that mean ‘scale’ and ‘wing’. There are believed to be over 180,000 scale wing species around the world and 160,000 of those are moths. Together, they make up approximately 10% of the known insect world. More than 11,000 moth species call the U.S. home.

Moth or butterfly?

The easiest way to tell if it’s a moth or butterfly is to look at the way they hold their wings while at rest. Generally speaking, moths hold their wings out to either side, while butterflies hold their wings upright, over their back. [butterfly/up – moth/out] You can learn more about the differences between moths and butterflies on my post about them. Did you know that moths have ears and butterflies do not? I didn’t either.

Moth lifecycle

Moths start out as eggs. Those eggs are normally laid in or around plant material. Some eggs are laid in the soil. When those eggs hatch, moth larvae (caterpillars) appear. Those larvae eat a lot. Seriously. It is that feeding that causes all the damage in the garden. Eventually, those caterpillars eat their fill and build cocoons around themselves. Within those cocoons, some pretty amazing changes take place. What started as a squishy, worm-shaped digestive system is transformed into a fuzzy, winged creature of the sky.

Good moths

Most adult moths only eat nectar. Some moths don’t eat at all. They simply do not have mouthparts and do not live long enough to need food. This nectar-feeding means that moths are important pollinators. In some parts of the world moths are an important food source and some moths give us silk.

Hummingbird moth (Dwight Sipler) CC BY 2.0

Hummingbird moths are an example of a daytime moth that acts as a pollinator. While most of their clearwing cousins are troublemakers, these lovely specimens are a good sign your garden has abundant biodiversity. In most cases, however, moths are not a gardener’s friend. Or rather, their offspring, the caterpillars, are not

Codling moth (Andy Reago & Chrissy McClarren) CC BY 2.0

Apple infested with codling moth larvae (Joachim K. Löckener) CC BY-SA 3.0

Bad moths

Bad moths infest our pantries, closets, and our gardens. They chew holes in flour bags, sweaters, and leaves. Here is a list of the most common garden variety problem moths:

• Achemon sphinx moths (Eumorpha Achemon)--grape pest
• Artichoke plume moths (Platyptilia carduidactyla)—serious artichoke pest
• Clearwing moths—a large family of boring caterpillars that damage many garden crops
• Codling moths (Cydia pomonella)--apple, pear, and walnut pests
• Corn earworm moths (Helicoverpa zea)—aka cotton bollworm; major agricultural pest
• Diamondback moths (Plutella xylostella)—common pest of cole crops
• European corn borers (Ostrinia nubilalis)—invasive corn pest
• European pepper moths (Duponchelia fovealis)—invasive new pest of several garden plants
• Gypsy moths (Lymantria dispar)—invasive pest of hardwood trees
• Fall armyworm moths (Spodoptera frugiperda)—invasive pest of several garden crops
• Five-spotted hawkmoth (Manduca quinquemaculata)—caterpillars, known as tomato hornworms, can devastate tomato crops*
• Leek moths (Acrolepiopsis assectella)—aka onion leaf miner; invasive pest of Alliums
• Lesser appleworm moths (Grapholita prunivora)— major agricultural pest
• Light brown apple moths (Epiphyas postvittana)—major agricultural pest
• Melonworm moths (Diaphania hyalinata)--cucurbit pest
• Orange tortrix moths (Argyrotaenia franciscana)—aka apple skinworms; major agricultural pest
• Oriental fruit moths (Grapholita molesta)--pome and stone fruit pest
• Wax moths (Galleria mellonella, Achroia grisella)—beehive pests

New threats to plant health are occurring all the time. For example, in 2005, a single European pepper moth was found in a shipment of begonias at a San Diego Home Depot. That serious pest is now found in 13 US states and Canada.

Five-spotted hawk moth (Andy Reago & Chrissy McClarren) CC BY 2.0

Tomato hornworm (Kate Russell)

*NOTE: If you come across a tomato hornworm covered with tiny white oval protrusions, put it into something it can’t escape from but that will allow those protrusions to hatch and fly away. They are beneficial parasitic wasps

Why are moths attracted to light?

For a long time, no one understood why moths are attracted to light. Now there’s a theory called celestial or transverse orientation. Having evolved before electric lights were invented, moths were believed to maintain a specific angle in relation to the moon to fly in a straight line. Since the moon is so far away, the slightly curved line they would fly really wouldn’t make much of a difference, relative to a moth. Add your patio light and moths just don’t know what to do with themselves. In fact, light pollution is believed to be partially responsible for a severe decline in moth populations around the world.

Artichoke plume moth (Kate Russell)

Moth management

Before you start adding mothballs to your closet (or the garden), you need to know that carcinogenic mothballs are bad for us. You can more safely protect your clothing from common clothes moths (Tineola bisselliella) by bagging it or adding cedar or juniper to your closet. You can use yellow sticky sheets or commercially available moth pheromone traps to take care of Indianmeal moths (Plodia interpunctella). Garden moths are best controlled by natural predators. That list of predators includes amphibians, bats, birds, cats, dogs, lizards, and even rodents. [I have trained one of my dogs to chase imported cabbageworm butterflies out of my garden. It’s fun to watch and sometimes she even catches one.]

Since it is the caterpillars that are causing most of the damage, observation and handpicking are often the best organic controls. Personally, I allow caterpillars to grow large enough to be worth feeding to my chickens. It’s a case of how much one is willing to tolerate.