Garden Q&A: For National Moth Week, take time to appreciate the diversity of these amazing, colorful insects
Welcome to National Moth Week! (July 23-31) As an insect enthusiast, I encourage everyone to take a closer look at the vast diversity of moths that fill our world. Butterflies and moths belong to the same insect group, but moths far outnumber butterflies in species diversity. Since many moths have muted colors or fly at night, we’re largely unaware of this bounty. Let’s take a quick appreciation tour of the group to reveal some of the amazing, bizarre, and quirky features of this major insect order.
Moth adults come in all shapes and sizes; like butterflies, wings are their most prominent feature. There are “micro-moths” mere millimeters long and giant silk moths nearly 6 inches across – North America’s largest. (Despite the name, they’re not in the same family as true silk moths.) The wings of some groups are so wispy you wonder how they fly. Others lay so flat at rest with their wings spread that you’d swear they were two-dimensional.
Some adults bear flashy colors and patterns in broad daylight because they’re chemically defended, similar to how monarch butterflies use milkweed toxins. Giant leopard moths, a black-and-white version of their namesake, exude distasteful golden droplets from their shoulders when disturbed. Wasp-mimicking species use warning colors to gain protection (who wants to risk a stinging snack?) while others use a different tactic, pretending to be inedible objects like lichen, twigs, dead leaves, or even bird droppings.
Occasionally, vivid markings are hidden behind camouflaged forewings which cover the body at rest. When disturbed, the moths flash their colorful hind wings or expose eyespots that stare back at the predator. These designs startle a predator into rethinking an attack, allowing escape or making the moth appear too big to handle.
For seemingly defenseless creatures (soft bodies with no stinger, jaws, or sharp projections), adult moths use some clever strategies for survival. Great camouflage is the baseline strategy, but some moths can hear ultrasound produced by hunting bats. When the flying moth hears a bat homing-in, the moth drops out of the sky and disappears from the bat’s radar. Milkweed tussock moth adults actually click back ultrasonically at a pursuing bat as a warning about their distaste, in case the bat already ate others and regretted it.
Blooms attractive to moths tend to be white or pale in color, or sometimes pink, dull red, or purple, and often have a strong, sweet scent, especially at night. As with butterflies, they prefer flower shapes or clusters that provide a “landing platform” where they can sit and sip nectar, though some rarely alight. Sphinx moths hovering at flowers are classic examples of “did I just see a small hummingbird?”
Moth caterpillars have a dazzling array of colors, patterns, and shapes. A few are spiny and irritate skin, like saddleback caterpillars that look like a terrier wearing a sweater. I have repeatedly been stung by accidentally brushing up against them, because they hide on leaf undersides. It smarts for a few minutes, but I still think they’re beautiful and adorable.
Some caterpillars resemble a walking toupee or dust bunny, like the flannel moths (another no-touch group). Slug caterpillars, while not actually slimy, include species whose body fringe looks like delicate spun glass. The monkey slug looks like some sort of faceless alien Muppet with a fun hairdo and a herky-jerky gait. (Don’t touch that one either.)
The weird slug caterpillar group also includes featureless speed bumps, with no discernable head or legs unless flipped-over. A few giant silk moth caterpillars have colorful knobs on their body or spiny horns that look like they belong in a rock band. (With a name like hickory horned devil, you can’t go wrong.) The caterpillars of other moth families have multi-hued patterns, fine stripes, marbling, squiggles, or big eyespots above their heads that mimic a snake staring you in the face.
When not feeding, many inchworms disguise themselves like leaf stems or twigs by standing on their hind legs ramrod-straight and freezing like a living statue performer. This family’s name is geometridae, which means “earth-measurer.” (And they do…once inch at a time.) One member, the camouflaged looper, decorates itself with bits of leaf or petal, becoming a walking parade float of flair. As it grows and eats new things, the costume changes.
While a very small number of moth caterpillars are home or garden pests, the great majority exist unnoticed and do not cause us humans any trouble. Plenty of caterpillars and adult moths feed hungry birds, bats, beneficial wasps, predatory bugs, and other organisms that help keep our ecosystem in balance. With over 2,500 moth species documented in Maryland to date, you could make a long-term hobby out of cataloging all the species found in just one yard. (A good gateway to developing an interest in all of the other wondrous insects you’ll encounter in the process!)
University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Extension” to send questions and photos.
