From beautiful vibrant orange Monarchs to vibrant spotted Swallowtails, butterflies are always a joyful sign of spring blooms in the garden. But could they actually be harming our plants?
Maybe this seems like a silly question, since most gardeners try to attract butterflies to their yard. Still, many gardeners get confused about whether or not butterflies are good for their vegetables.
While there are many beneficial butterflies, there are a few pesky moths and butterflies that may actually do loads of harm to vegetable crops. Let’s dig into the details and sort out the differences between the two and how to spot a pest butterfly in your garden.
- 1 Butterflies: An Overview
- 2 Do They Harm Plants?
- 3 Lifecycle
- 4 Can Butterfly Caterpillars Kill Plants?
- 5 Butterflies vs. Moths
- 6 Cabbage White Butterflies (Pieris rapae)
- 7 Cabbage Moths (Plutella xy-lostella)
- 8 Organic Control of Cabbage Loopers
- 9 Final Thoughts
Butterflies: An Overview
Butterflies are members of the order Lepidoptera, along with their cousin moths. They provide many benefits including pollination and supporting healthy wildlife ecology.
Unfortunately, due to widespread pesticide use and habitat destruction, many butterflies, like the famous Monarch, have become endangered. Butterflies are indicator species, meaning they are very sensitive to changes in the environment and if they start dying off, we know an ecosystem is in trouble.
Do They Harm Plants?
Butterflies are not directly harmful to plants. The main culprits are actually cabbage moths and white cabbage butterflies (which we describe below). Almost every other butterfly is virtually harmless!
Some leaves may die when white cabbage butterfly eggs are laid on them, but most butterflies and skippers are not the ones to blame for plant damage.
A 2017 study found that this plant defense mechanism mainly happens to cabbage-family vegetables in response to the cabbage white butterfly. Basically, eggs need humidity to hatch and a food source (succulent fresh leaves) for the emerging cabbage worm caterpillars.
A dry, dead leaf would reduce the likelihood of the eggs surviving and hatching. This is a really smart move on behalf of the plant, but as you can imagine, lots of cabbage butterfly eggs could lead to lots of leaf loss.
So the butterflies themselves aren’t technically harming any plants- it’s their newly hatched hungry caterpillars who do the chomping.
We all learned in school how caterpillars go into cocoons and emerge as butterflies. This is called a “complete metamorphosis” because the young are very different from the adults. In this beautiful transformation, a tiny egg eventually becomes a majestic butterfly!
In contrast, an “incomplete metamorphosis” (as in grasshoppers, crickets, and dragonflies) means that the babies just look like smaller versions of adults without wings.
Adult butterflies are completely harmless, but those mischievous youngsters are really the ones we have to look out for.
Four Stages of Butterfly Lifecycles
Egg: adult females lay tiny eggs on the underside of plant leaves that the emerging larva can feed on
Larva: commonly called caterpillars, these are basically the teenager butterflies who cannot stop eating and growing \
Pupa: once it is full grown, caterpillar soon goes into a chrysalis or cocoon dangling from a branch or leaves, or hidden underground- this is where the magic happens
Adult: after a few weeks to a month or more, an adult butterfly emerges as a flying graceful beauty ready to lay more eggs and repeat the cycle
Can Butterfly Caterpillars Kill Plants?
Eh, not really.
This may surprise you when you think about tomato hornworms, leaf rollers, loopers, leafminers, and cutworms. But none of those caterpillars come from true butterflies! They are moths.
Butterfly caterpillars simply aren’t major pests.
Butterflies vs. Moths
So what’s the difference between butterflies and moths?
Both of these fluttery insects belong to the order Lepidoptera. The name of this order comes from the Greek words lepido (scale) and pteron (wing).
Lepidoptera is a Latin classification of over 180,000 classified species of butterflies, moths, and similar insects. Almost all Lepidopteran larvae are called caterpillars.
Butterflies and Moths Commonalities
Butterflies and moths are very similar and share many commonalities:
- Four wings typically covered with scales
- Hind wings tend to be smaller than the front ones
- Sucking mouthparts (called a proboscis) that act like a straw to suck nectar out of flowers
- Larvae are called caterpillars
- Four-stage metamorphosis (egg-larva-pupa-adult)
Differences Between Butterflies and Moths
|Mostly active in daytime (diurnal)||Mostly active at night (nocturnal)|
|Mostly brightly colored (a few dark brown members with markings)||Mostly duller colored (with a few day-moth exceptions)|
|Fold wings upright and together when resting||Hold wings flat when resting|
|Simple antennae have clubbed tip||Feathery antennae with no clubbed tip|
So, as you can see, they can be a little difficult to tell apart. The easiest way I’ve found while in the garden or field is to watch a Lepidopteran land on a flower or leaf.
If the wings fold up while it’s resting, I know it’s a butterfly. If the wings lay flat (and it’s closer to nighttime), I know it’s a moth.
Cabbage White Butterflies (Pieris rapae)
These guys are the exception to the rule. Cabbage White Butterflies are true butterflies and their caterpillars are not friends to a vegetable gardener. And to make things extra confusing, people often call these white butterflies “Cabbage Moths.”
These white-winged butterflies lay eggs that hatch into cabbage worms: caterpillars that are extremely ravenous for Brassica-family plants, which include some perennial vegetables. The most common Brassica-family plants you’ll find them near are:
- Bok choy
- Brussels Sprouts
Identifying a Cabbage White Butterfly
To identify a Cabbage White Butterfly (Pieris rapae), start noticing any white butterflies around your garden. Are they landing or hovering near Brassica plants? Do they have any of the following traits?
- 1.75” to 2.25” big
- White to silvery wings with grey wingtips (underside of forewings may be light yellow or pale green)
- Prominent antennas with little balls or “clubs” on the tips
- Males have one black dot in the center of the forewing; females have two black dots
- Caterpillars are pale green to bluish with many black spots, prickles, and a yellow line down the back
- Caterpillars hang out on the underside of Brassica leaves and eats holes through the middle
- Frass (caterpillar poop) is bluish-green on leaves or in heart of cabbage
Cabbage Moths (Plutella xy-lostella)
Cabbage Moths are the adult versions of cabbage loopers, which do the same type of damage as cabbage worms described above.
Even though people call White Cabbage Butterflies the name “Cabbage Moths,” true Cabbage Moths are actually small and brown.
Their whitish eggs are laid under Brassica leaves in the same way as the White Cabbage Butterfly. When they hatch, the caterpillars are equally as ravenous.
Identifying Traits of a Cabbage Moth
- 1 to 2” greyish-borwn or black with kidney-shaped markings and white accents
- Hindwings are darker than forewings
- Wings stay open when it lands (because it is a moth)
- Active in evenings or at night
- Furry whitish brown eggs
- Caterpillars are green-brown
Organic Control of Cabbage Loopers
The easiest way to protect against both Cabbage White Butterflies and Cabbage Moths is to simply use row cover.
This thin fabric allows sunlight and water through but acts as a physical barrier to the insects. The adults can’t lay their eggs on your Brassicas, therefore no caterpillars can damage the leaves.
Another common organic control is called Bacillus thuringiensis or Bt. This is a toxin produced by a soil bacterium that specifically attacks and kills caterpillars. It is a form of biocontrol that is not harmful to other insects.
However, there is evidence that it can harm Monarch caterpillars, so I would only recommend using this if you have a serious infestation. Otherwise, physical barriers and beneficial habitat are plenty.
If your garden is small enough, you can search for the greenish frass (caterpillar poop) of cabbage worms and cabbage loopers, then find the pests and pull them off by hand.
Better yet, find the little white or yellow eggs and remove them before the caterpillars hatch. This is obviously not a viable solution at a larger scale, but it works great for just a few Brassica plants in a small garden.
There you have it! Most butterflies are completely harmless and in fact beneficial to your garden. The primary exception is the White Cabbage Butterfly (commonly confused with the name Cabbage Moth).
Look out for these white butterflies around your garden and take appropriate preventative methods. Any other colorful bright butterflies are only helping to pollinate your flowers, support the ecosystem, and add beauty to the landscape.