Orange Sulfur Butterfly – Species Profile & Facts

Orange Sulfur (Colias eurytheme) is a distinguishable species that not everyone will observe in the nature. That’s because the butterfly’s nocturnal feeding habit limiting its activity throughout the day.

This is one of the most curious butterfly species with a rather common appearance but revealing spicy details at a closer look.

Let’s discover what we can dig out about the Orange Sulfur or the alfalfa butterfly, as it’s also commonly called.

How to Recognize an Orange Sulfur Butterfly?

To an untrained eye, you have a yellow or orange butterfly with 2 tiny black spots on its forewings and wide, colored bands on the wings’ margins. These bands are only visible from a dorsal view since the butterfly displays a different pattern on the underside of its wings.

Orange Sulfur butterflies have differently-colored wings, showing as dark yellow or orange on their dorsal side, and light yellow, almost white on the ventral side.

But this is what you can see with a naked eye at a first glance. The real interesting aspect is what follows next.

It seems that males’ wing color reflects ultraviolet light, whereas females reflect it. This core difference comes from the fact that the males’ wings are covered by scales that contain pterin. These are pigments that reflect all light wavelengths below 550 nm.

The same pigments seem to be responsible for a higher ultraviolet contrast between the Orange Sulfur male and female and the UV-absorbing background, namely vegetation. This feature is not common in the Lepidoptera world, making the Orange Sulfur unique in this sense.

We will discuss the purpose of this feature later on in this article.

What Does an Orange Sulfur Butterfly Caterpillar Looks Like?

This species’ caterpillar is rather inconspicuous. It displays a uniform green and a smooth body, lacking any segments that are so typical to other species. Adult caterpillars (4th, 5th instar) will also showcase well-defined white or yellow lines traversing the body on both sides.

The contrast between the caterpillar’s green body and the yellow lines makes it stand out to a trained eye. Thanks to its dietary preferences, this coloring is actually beneficial to the caterpillar. The Orange Sulfur caterpillar will spend most of its life on alfalfa plantations, consuming a variety of plant species, most of which belong to the Fabaceae family.

These provide the caterpillar with a green cover, boosting its camouflaging abilities.

How Big Does Orange Sulfur Butterfly Get?

This species will only reach around 2 inches in wingspan, ranking the butterfly as a medium-sized butterfly in the Lepidoptera genus.

Where do Orange Sulfur Butterflies Live?

The Orange Sulfur prefers North America as its main residence. You can encounter this species from southern Canada to northern Mexico. They prefer warmer regions with temperate climates and will gather in open areas for agricultural reasons, providing rich food sources.

Moderate and stable temperatures are necessary to ensure successful reproduction and provide the larvae with a hospitable environment.

What do Orange Sulfur Butterflies Eat?

This species ranks as a pest due to its specialized diet. The Orange Sulfur butterfly has 2 distinct feeding patterns:

– As a larva

The larva will consume a variety of plants in the Fabaceae family. These include clovers and sweet lovers, goldenbanners, lupines, and, of course, alfalfa. Most Orange Sulfur butterfly species prefer the latter since alfalfa has a longer lifespan than other plant species. It generally lasts until the end of summer, sustaining the butterfly’s development consistently during this time.

Given that Orange Sulfur butterflies mate several times over the course of multiple days, and females may lay hundreds of eggs, this species’ reproductive rate is enormous. This will eventually result in the entire population of caterpillars invading alfalfa crops and other similar plants and destroying them systematically.

Knowing that the Orange Sulfur larvae can cover large areas and arrive in obscene numbers, pesticides aren’t really feasible. This only leaves room to biological control, creating the ideal conditions for the caterpillar’s natural predators to thrive in its environment.

Some of the most proficient Orange Sulfur predators include several varieties of wasps from different families like Ichneumonidae, Sphecidae, and Vespidae. Some of these kill caterpillars and bring them to their young as food, while others use them as hosts for their offspring.

The latter are parasitic wasps, falling in the same overarching category as the Tachinidae flies and important pest-control agents.

If the caterpillar population reaches critical thresholds, Bacillus thruringiensis is a good alternative for controlling the larvae. This is a naturally-occurring bacteria that lives in the soil and is toxic to some insect species, primarily their larvae. It is harmless to all mammals, humans included, and insects like wasps, bees, and flies, but it’s fatal to Orange Sulfur caterpillars.

– As an adult butterfly

The adult consumes nectar primarily from a variety of plants like clover, alfalfa, milkweed, and most specimens belonging to the Asteraceae family (sunflower is one of them). This leads the adult butterfly also to prefer feeding areas similar to its larvae.

The adult’s feeding pattern may be considered beneficial since it contributes to plant pollination. However, the benefits are quickly overshadowed by the larvae’s drastic economic impact.

 What Plants Attract Orange Sulfur Butterfly?

The adult butterfly prefers plants like aster, milkweed, and goldenrod, as it provides them with all the necessary nutrients to survive and thrive. The female will almost always prefer larvae-compatible plants when laying its eggs to make sure that the grubs have immediate access to foods.

The main host plants include alfalfa, white clover, milk vetch, crown vetch, and others.

How do Orange Sulfur Butterflies Reproduce?

Unlike other Lepidoptera, the Orange Sulfur butterfly doesn’t resort to extensive mating behavior. The foreplay is cut short as the butterflies focus on reproduction more than anything else. The courtship is essentially diluted to females choosing males based on their UV reflection.

The reverse is also true. Male Orange Sulfur butterflies identify the female by their UV-absorbing coloring. They can also spot the UV-reflecting pattern displayed by other males, so they know who to avoid.

An interesting aspect is that Orange Sulfur males showcase varying levels of UV reflection. The intensity depends on their age, health, and sexual maturity, among other factors. The females can tell immediately and will either accept or reject the males on those grounds.

Male butterflies produce a spermatophore, containing the sperm and additional nutrients meant to nourish the female. The younger the adult, the larger and richer the spermatophore, which is why Orange Sulfur females will prioritize younger males over the older ones.

The female’s body breaks down the spermatophore and extract the sperm to fertilize the eggs. Once the process completes, the female will mate again to increase the number of fertilized eggs.

Once the reproductive process is complete, the female will begin to lay the eggs, triggering the butterfly’s life cycle. This consists of the typical 4 phases:

  1. Egg – The Orange Sulfur female will lay the eggs one at a time. These are white or yellow formations, oval in shape and rather pointy, spread all over the leaf’s surface. The female will lay several dozen eggs a day for up to 700 to 1,000 eggs during the entire reproductive season. The eggs will typically hatch around 4 to 5 days later.
  2. Larva – The larva begins to feed almost immediately upon hatching and can eat quite a lot, eventually reaching to 1.4 inches in size by the end of its 5th instar. The caterpillar’s growth stage can be identified by assessing its feeding pattern. Younger caterpillars will poke holes in the leaves and chew on their tips. Older caterpillars will eat the leaves from the margins towards the center and will only consume about half a loaf. They will then move on to another one.
  3. Pupa – The chrysalis will form 15-20 days later, depending on environmental conditions. The larvae that get the most food may pupate earlier. Overwintering species will produce hibernating pupae.
  4. Adult – The adult is ready to fly and eat several hours following hatching and becomes sexually mature within 4 to 5 days.

Interesting fact: the male’s sperm may actually be toxic in nature. This could explain why virgin females, unable to mate, always live longer than those with at least one mate.

Where do Orange Sulfur Butterflies Lay Their Eggs?

The Orange Sulfur female will lay the eggs on the larvae’s preferred plants, including alfalfa, vetch, clover, etc. The eggs are generally white at first, with pointy ends, and become orange or even red when getting ready to hatch several days later.

The female’s egg-laying behavior provides the future larvae with plenty of food at their disposal, and one female can infest a good chunk of alfalfa crops.

Are Orange Sulfur Butterflies Rare?

While the butterfly population has decreased naturally across the board, this species is rather common in its native areas. The Orange Sulfur butterfly remains contained to North America some regions in Europe and Asia and doesn’t show any signs of becoming rare anytime soon.

Even with natural predators roaming their territory, human deforestation and habitat changes, and active anti-pest strategies, the Orange Sulfur seems unaffected. There are no official numbers to quote, but the general consensus is that this species is doing just fine.

Is the Orange Sulfur Butterfly Endangered?

Quite the contrary. The Orange Sulfur butterfly thrives in many areas of the globe thanks to its outstanding resilience and extreme reproductive rates. Very few butterfly species are as prolific as the Orange Sulfur butterfly when it comes to spreading their genes.

The Orange Sulfur female will lay up to 1,000 eggs, spread over a large surface to ensure the survival of as many larvae as possible. This approach minimizes the impact of natural predators like birds, wasps, spiders, ants, or rats on the species, allowing it to thrive when others decline.

How Long do Orange Sulfur Butterflies Live?

The typical lifespan of an Orange Sulfur butterfly is 2 to 4 weeks. This is typical for most Lepidoptera. Overwintering species, however, may extend that duration to a year if we include the hibernation period.

Generally speaking, all Orange Sulfur butterflies have the ability to hibernate through the winter, but not all will survive the cold season.

What is the Meaning of Orange Sulfur Butterfly?

The butterfly’s popular name is a descriptor of its appearance, while the Latin name has some unverified origin suggestions that I would take with a grain of salt. You may see some articles mentioning that eurytheme comes from the Greek God Apollo’s sister, but Apollo didn’t have a sibling called eurytheme or any variation of the name.

So, the butterfly may have gotten its Latin name due to the fact that it sounds nice.

Is the Orange Sulfur Butterfly Poisonous?

No, despite the butterfly’s name suggesting otherwise. It all goes back to what I was saying about some names just sounding nice. Orange Sulfur has a lot to do with the butterfly’s appearance and nothing to do with its content.

This species is perfectly palatable to a variety of predators, which has forced the butterfly to adopt other defense mechanisms to ward them off. There are overall 4 defensive measures that the Orange Sulfur butterfly uses to keep evade predators:

  • Larval camouflage – The caterpillar displays a uniform green, allowing it to blend in with its environment. This minimizes its visual print, making it more difficult for predators to spot it.
  • Adult camouflage – The adult Orange Sulfur butterfly displays 2 black spots on its forewings, reminding of eyes. These can sometimes intimidate predator birds that spot the butterfly from above, discouraging them from attacking. ‘Sometimes’ is good enough.
  • Adult flight pattern – The adult butterfly is a fast and erratic flyer. It will swoosh across the fields, using its body movements to evade potential pursuers and escape whenever possible.
  • Over-reproduction – This is probably the best defensive tactic available to animal species that have no defensive tactics. It’s simply multiplying at a higher rate than predators can kill them. The female Orange Sulfur can lay up to 1,000 eggs in one mating season and spread them across a wide area on multiple plants. Many of them will fall prey to predators, while many others will hatch just for the caterpillars to meet the same fate. But many others will survive thanks to the female’s ability to throw more offspring at predators than they can consume.

As you can see, the Orange Sulfur butterfly has no use for poison.


This invasive species is the protagonist of a compelling story about adaptability and resilience. That being said, the Orange Sulfur butterfly isn’t immune to all deterrents.

People have been using biological suppression mechanisms with great effect by introducing the butterfly’s natural predators into its habitat. This approach minimizes the butterfly’s harmful impact on human crops while keeping their numbers sufficient to maintain their pollinating effects intact.

For now, this is a win-win situation.

Butterflies   Updated: January 31, 2022
avatar Welcome to Insectic, a blog to learn about insects and bugs. I'm Richard, and I've created this website to share my experience, knowledge, and passion with others.

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