Moths

Media
Forage looper moth perched on a brick wall, viewed from side
Scientific Name
More than 12,000 species in North America north of Mexico
Family
About 80 families in North America in order Lepidoptera that are not butterflies or skippers
Description

In North America, the Lepidoptera — the insect order comprising all the moths and butterflies — contains more than 30 superfamilies (groupings of families). One superfamily (Papilionoidea) contains all the butterflies and skippers. But all the rest of the lepidoptera are called moths. Like butterflies, moths have tiny, overlapping scales on their wings. These seem like dust when they rub off onto your fingers. The scales can be brightly colored, or they can be drab.

More than 12,000 species of moths occur in North America north of Mexico. Most of us have a general idea of what a moth looks like, but to be certain, note the following characteristics:

  • Antennae, in moths, are filaments that lack a club at the tip; sometimes they are shaped like feathers.
  • Moths typically fold their wings over their body like a tent, or flat but swept back at an angle to the body, looking triangular from above. (Butterflies, when perched, typically hold their wings straight out to the sides, or hold them together, straight up over the body.) (There are exceptions.)
  • During metamorphosis, the pupae of moths are often wrapped in a silk cocoon and frequently are positioned on the ground amid leaf litter or underground. The cocoons often incorporate bits of leaves, twigs, or other materials. (In butterflies, the chrysalis is usually attached to a plant or other object, and it is not enclosed in a cocoon.)
  • When does it fly? Moths are usually most active during at night, while butterflies are usually active during daylight hours. (Again, there are exceptions.) Many moths are attracted to lights at night.
  • Moths often have relatively thick bodies, compared to butterflies (though members of the skipper family of butterflies have thicker, mothlike bodies).
  • The larvae (caterpillars) of several kinds of moths are agricultural or other pests. Few butterfly larvae are considered economically destructive (though there are exceptions).
  • Adult coloration varies greatly, but most moths are drab gray or brown, much less colorful than many butterflies. (Again, there are plenty of exceptions.)

Missouri’s Moth Groups

Missouri has far too many moth species to cover in this nontechnical guide. Some species are so unique that you can identify them by a quick look at a picture. But in many cases, identifying moths “to species” requires scientific manuals and a microscope to see details of various body structures and wing vein patterns — or consulting an entomologist.

However, it is not too difficult to learn how to identify some of the major families of moths. Any of our various sphinx moths, for instance, can be identified by its large size, heavy body, long, pointed abdomen, and hovering flight. As another example, plume moths are small and slim, have drab colors, and rest with their wings in a characteristic T shape. Pat yourself on the back when you can begin saying things like, “That looks like some kind of tiger moth.”

Where To Find
Statewide. Different moths occur in different habitats, which usually correspond to the locations of their larval food plants.

Where do you find moths? Nearly anywhere, but here are some hints:

  • Look for moths near their host plants. These are the specific types of plants upon which a species must deposit its eggs, because its caterpillars can only eat those certain types of plants. Adults must be near these plants to mate and lay eggs. Also, because that’s where they lived as caterpillars, they are near host plants at the very beginning of their adult lives. So — for example — it’s reasonable to look for grapevine sphinxes in wooded bottomlands where grapevines grow.
  • Although some moths never eat as adults, others can be seen taking nectar from flowers, sugar from rotting fruit or tree sap, or moisture from mud, wet sand, or other damp ground.
  • Another way to see moths is to look for them around electric lights at night. Collectors hang a white bed sheet in an open area and rig up different types of light (such as black lights, incandescent, and so on) to shine on it. Different moth species are attracted to different wavelengths, and they land on the sheet where you can see them.

Moth conservation involves the same issues as many other animals, chiefly centering around habitat disruption and loss. While many moths can live on a wide variety of plant hosts, others can only survive on very particular plant species, which occur in specific native habitats, such as high-quality tallgrass prairie. Also, as with other insects, moths can be killed by indiscriminate use of pesticides. (Meanwhile, the larvae of several moth species are serious agricultural pests that are the targets of those pesticides!)

As with butterflies, moths do nearly all their growing as caterpillars, so that’s when they eat the most. Different species eat different foods, with most eating plant foliage. Still, among the thousands of moth species, some bore into plant stems or roots, some are leaf miners (tiny caterpillars that eat the inside layers of a leaf), and some use silk to fold over leaves to make a shelter while they feed. Some are generalists, eating a wide variety of plant types, while others are limited to certain plant families (for example, oaks, nightshades, or grasses), plant genera, or even to a single plant species.

Some moth caterpillars eat dead plant matter, such as paper, including wallpaper; animal materials, such as leather, wool, fur, and feathers; or fungi. Grain, carpet, and clothes moths are notorious.

Most moths spend only a few weeks as an adult, so they typically take moisture and nutrients only to maintain themselves as they find mates, mate, and lay eggs. The adults of some moths lack functioning mouthparts and cannot eat — these include the spectacular large saturnids such as the luna, cecropia, and polyphemus moths — their inability to eat helps explain their brief lives as adults.

Several moths are Species of Conservation Concern in Missouri, meaning that their numbers may be declining or their presence in our state may be threatened. Among these are the marbled and precious underwing moths, a noctuid moth called Dichagyris reliqua, and a geometrid called Lytrosis permagnaria.

The caterpillars of several moth species feed destructively on trees, shrubs, flowers, vegetables, and crops. They can range from simple nuisances to economically significant pests. One example is Agrostis ipsilon: as an adult, this noctuid moth is called the ipsilon dart, but the larva — called the black cutworm — can be a serious pest of corn, soybeans, cotton, lawn grass, and garden plants.

Some moths have a special capacity for destruction. One of these is the invasive gypsy moth, a native to Europe whose larvae feed on oaks and many other species. With few natural enemies in North America, gypsy moth infestations can kill thousands of trees, destroying much of our forest resources.

Life Cycle

Moths, like beetles, bees, and flies, undergo complete metamorphosis: after a series of wormlike juvenile (larval) stages, they enter an inactive phase called a pupa, then emerge as sexually mature, winged adults. (Other insects, such as grasshoppers and true bugs, have juvenile stages that look more or less like the adult form, only smaller and minus the wings — their life cycle is called incomplete metamorphosis.)

Some species have only one brood a year, while others have two or more.

Moths begin life as eggs that are typically laid on or near the host plant or other larval food source. The larvae (caterpillars) hatch from the eggs and begin eating and growing. As they grow, caterpillars repeatedly molt into larger exoskeletons (“skins”). Each stage is called an instar. The caterpillars within a single species may look different upon each molt.

When the caterpillar has eaten and grown sufficiently, it typically burrows into the soil surface leaf litter and enters the pupal stage. The pupa is usually protected by a silken cocoon, often with bits of leaves or other materials incorporated into it.

Different moth species overwinter at different points in the life cycle: some overwinter as eggs, some at different points in the caterpillar development, and some as the pupa. A few overwinter in sheltered places as mature, winged adults. Most species only live a few days or a few weeks as winged adults.

Moths are attracted to lights at night, and the image of a moth hopelessly attracted to a flame — often leading to its death — has long been used in poems, music, and stories. Why are they (and other insects) so attracted to lights? Biologists have several ideas, but so far there’s no single clear answer. One idea is that our many bright lights disorient them. Moths evolved as nocturnal animals with usually only one bright light to be seen: the moon. The nervous systems of moths and other insects might be coordinated to use that extremely distant point of light as a navigation beacon — always keeping the moon at a certain position relative to their body. But when presented with a bright nearby light, their simple navigation system cannot compensate, so they spiral closer and closer toward it.

There is evidence that some populations of moths, living in cities, might be so disrupted by light pollution that they are losing their instinct to fly. But if they don’t fly, how will they find mates and reproduce? And what happens to the plants they pollinate?

In the past, many people used mothballs to prevent the larvae of clothes moths from chewing holes in their clothing. Because of safety concerns and their unpleasant smell, and because of improvements in cleaning techniques and clothing storage, mothballs have lost their popularity.

The University of Missouri Extension division provides helpful information on caterpillars (most of them moths) that feed destructively on trees, shrubs, flowers, vegetables, and crop plants.

Silk, used for making the fabric, is created by the caterpillars of certain moths, especially Bombyx mori, an Asian species. Attempts to raise silkworms in North America are one reason white mulberry (their primary host plant, native to Asia) was introduced to our continent. That mulberry species is now considered a noxious weed.

Moths that take nectar from flowers play a role in pollination. Night-blooming flowers need night-flying pollinators. An example is jimsonweed, also called sacred datura; its large, white, trumpet-shaped flowers open in the evening. They are pollinated by sphinx moths.

Many, many animals eat moths, including spiders, praying mantises, toads, frogs, lizards, snakes, bats and other mammals, and birds (especially owls and whippoorwills). Moth predators commonly wait near electric lights. If you see spiders building their webs near your porch lights, you can bet that moths are a favorite food.

Most moths don’t survive to the adult stage, since there are plenty of predators to eat them as eggs, caterpillars, and pupae. Also, parasitoids (such as some fly and wasp species) lay their eggs on or in caterpillars — and their young eat the caterpillar from the inside.

Many bats prey especially on moths. Biologists have uncovered an interesting defensive adaption possessed by noctuid moths. A flying bat uses its radar-like echolocation to find and target individual moths. But a noctuid moth usually begins flying erratically — diving or cartwheeling — right before a bat swoops to get it. It turns out noctuid moths can hear the pulses of ultrasonic sound made by bats, sense their archenemy’s position and movements, and reflexively make appropriate evasive maneuvers. Meanwhile, at least some species in the tiger moth family take this a step further, creating their own ultrasonic sounds and timing their blips to jam the attack calls of bats.

Moths are commonly camouflaged in mottled shades of gray and brown. But some have striking eyespots on their hindwings, which they abruptly expose when disturbed. This startling appearance of a huge pair of “eyes” may make a predator pause long enough to let the moth fly away.

Tiger moths are typically bright orange, yellow, or red plus black. Like monarch butterflies, the plants they eat as caterpillars can make them toxic or distasteful to their predators. The color scheme — which is also used by bees, wasps, and stinging insects — serves as a warning to potential predators, and ultimately a defense.

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About Butterflies and Moths in Missouri
Butterflies, skippers, and moths belong to an insect order called the Lepidoptera — the "scale-winged" insects. These living jewels have tiny, overlapping scales that cover their wings like shingles. The scales, whether muted or colorful, seem dusty if they rub off on your fingers. Many butterflies and moths are associated with particular types of food plants, which their caterpillars must eat in order to survive.