Is it possible that butterflies are harmful to plants?
This seems like a silly question.
“Haven’t you ever heard of butterfly gardens? Most gardeners want to attract butterflies.”
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The idea that they could be harmful seems like pure nonsense.
And yet, here I am, writing an article about it. So, there must be something more to this answer than a simple “no.”
Are butterflies harmful to plants? Butterflies themselves are not harmful to plants. However, leaves on a plant may die in response to butterfly eggs being laid on them. At the same time, butterflies pollinate flowers and are an indication of overall healthy wildlife ecology.
What Is A Butterfly?
Inside the order Lepidoptera, there are true butterflies, skippers, and moths. True butterflies and skippers are grouped together in the term butterflies because they both fly during the day and have similar antennae structures.
An adult butterfly is not harmful to plants. Butterflies drink nectar, bask in the sun, and rest near puddles. These activities have no negative effects on plant life.
However, butterflies have four life stages. The adult stage is easy-going, but the three stages of childhood can be a little messy:
- Egg – Adult butterflies lay eggs on leaves and stems. Eggs are small, round, and stuck to a prime food source for caterpillars.
- Larva – Caterpillars are known for being destructive. Their whole purpose is to eat as much as possible to store energy for their metamorphosis.
- Chrysalis – Caterpillars will attach themselves to firm surfaces to begin forming a chrysalis. Inside the chrysalis, the caterpillar is completely broken down, and built back up into an adult butterfly.
Can Butterfly Eggs Harm Plants?
Surprisingly, yes. A recent study observed how plants in the Brassica family reacted to eggs deposited from the cabbage white butterfly. Butterflies lay eggs on plants that caterpillars will eat, so it’s no surprise that the cabbage white butterfly eggs will hatch into cabbage worms, who then eat cabbage and all its cousins.
In response, this study found that the plants would kill off the leaves where the eggs were laid. Eggs need some humidity to hatch, and a living leaf can help provide shade and moisture. A dead, dry leaf would greatly reduce the humidity surrounding the eggs and decrease the likelihood that the eggs would survive.
The plant’s defense mechanisms had varying degrees of success, with the most important factor being how clustered the eggs were. Tightly clustered eggs had a higher chance of surviving.
Depending on the number of eggs laid on an individual plant, this defensive response could result in large amounts of leaf loss, which could weaken the plant as the caterpillars emerge.
Can Butterfly Caterpillars Harm Plants?
You’re probably expecting my answer to be a resounding, emphatic YES!
But I’m going to go with… meh.
“What about those nasty tomato hornworms? Those are caterpillars!”
“What about loopers and leaf-rollers?”
“What about cutworms and armyworms?”
“Don’t even get me started on leafminers and tent caterpillars!”
I hear you, and if I was writing an article on moths, you would have a point.
But… I’m not. This is an article about butterflies. And butterfly caterpillars just don’t make the Top 10 Caterpillar Pests too often.
Cabbage white caterpillars
These guys are the exception. If you’re growing a vegetable garden and notice holes in your brassicas, these little worms are to blame.
In the caterpillar stage, cabbage white caterpillars are called imported cabbage worms. This is different from cabbage loopers, the cross-striped cabbageworm, and cabbage maggots.
Imported cabbage worms will target:
- Bok Choy
- Brussel sprouts
They can also attack nasturtium, sweet alyssum, and some cruciferous weeds.
Depending on your climate zone, imported cabbage worms will produce 3-8 new generations each spring and summer.
Worms are about an inch long, green, and fuzzy. They have a faint yellow coloring down their sides and backs.
When imported cabbage worms first hatch, they eat the surface layer of leaves, and leave behind an opaque scar. As the worms grow, they will progress to chewing large holes through leaves, and boring through heads of cabbage. Worms leave behind fecal matter that can build up and contaminate the spaces between tightly-formed leaves. Pellets will be dark green and build up at the base of leaves.
There are many ways to control imported cabbage worms, but the easiest is to stop planting brassicas. If you can’t live without your Brussel sprouts, try companion planting. Tansy and thyme are reported to repel imported cabbage worms, and they are easy to plant in your brassica beds.
The one other butterfly caterpillar that we found to cause damage was the Painted Lady butterfly. However, it targets thistles, which makes it a beneficial caterpillar in my opinion.
Can A Butterfly Chrysalis Harm Plants?
No. Most butterflies use plants for a stable, protected shelter during their metamorphosis.
Unless, of course, the chrysalis is that of an imported cabbageworm.
The chrysalis does not do any direct damage to your crops. However, the worms will overwinter on plant material, and reemerge the following spring to wreak havoc on your brassicas. This is a crucial life stage for subsequent generations.
If you find the pupa of these worms, pull the plant and destroy it to disrupt the lifecycle.
Can Butterflies Help Plants?
Yes. Butterflies will pollinate flowers as they drink. They aren’t too important for major food crops, but they are perfectly suited to pollinate native wildflowers.
Butterflies are an indication of the ecological health for an area. Butterflies are fragile members of an ecosystem, and a decline in native populations can signal an imbalance or disruption in the local wildlife.
You can help support local butterflies by planting native host plants.
How Can I Plant A Butterfly Garden?
Butterflies rely on certain host plants to reproduce. Planting native wildflowers will help maintain local butterfly populations.
Butterflies like bright, sweet-smelling clusters of flowers.
Start attracting butterflies to your garden by planting:
- Butterfly bush
- Butterfly weed
Provide a small, shallow dish with a thin layer of soil in the bottom. Place some flat rocks and damp sponges inside for the butterflies to puddle. Damp soil allows butterflies to soak up the minerals they need, and the rocks give them a place to land.
Most butterflies are beneficial to your garden. The caterpillars that cause the most damage in your garden are almost always the larva of a moth. You can encourage butterflies into your garden without worrying about a devastating caterpillar infestation (just don’t plant decorative broccoli).
Do you want to attract wildlife to your garden? Be careful you aren’t attracting unwanted guests into your landscape.
Can Moths Harm Plants?
Adult moths do not generally harm plants. However, moth larva can destroy entire crops. Caterpillars that are blamed for plant damage are almost always young moths. There are 16x more moth species than butterflies, and many can cause real damage on fruit trees, flowers, or vegetables.
Should I Release Butterflies Into My Garden?
Butterflies are beneficial insects, but you should not purchase them to release into the wild. Butterfly populations are fragile, and introducing a new species, or even the same species from a different location, can drastically alter the ability of native butterflies to survive. Do what you can to encourage wild butterflies to thrive, but don’t purchase your own.