Large Blue Butterfly: Identification, Life Cycle, and Behavior

Discover the fascinating world of the Large Blue butterfly. From its unique identification features and intriguing life cycle to its remarkable behavior, this article offers you in-depth insights.

Equip yourself with the knowledge of the major threats facing Large Blue’s populations, and learn what measures you can take to help conserve this beautiful species.

Large Blue butterfly

What is the Classification of Large Blue?

The scientific name of the Large Blue is Phengaris arion, a species that falls under the Lycaenidae family. This epic group, Lycaenidae, containing almost 6,000 species worldwide, is in fact one of the largest families within the Lepidoptera order.

The Large Blue, therefore, is classified as one of the 200-plus species of blue butterflies that inhabit the UK.

As a species of blue butterfly, its subfamily is the Polyommatinae. Moreover, these blue butterflies are under the tribe Polyommatini.

Like its fellow tribe members, the Large Blue showcases an aesthetically pleasing varying shade of blue wings, serving as both camouflage and a mating signal.

The Large Blue’s genus, Phengaris, is especially notable. Why? Because few butterfly species employ such fascinatingly complex survival strategies as does this genus, which even includes manipulating other insect species!

The Large Blue is truly a unique and captivating testament to evolutionary creativity.

The Large Blue’s classification underscores its uniquely captivating natural history.

Lycaenidae family, Polyommatinae subfamily, Polyommatini tribe, and Phengaris genus – these stages of classification all contribute to shaping the Large Blue’s exceptional characteristics, behavior, and life cycle.

What is the Distribution of Large Blue?

The Large Blue butterfly, scientifically known as Maculinea arion, has a distinct geographic distribution. Primarily, you’ll find this species across Europe, Asia and North America. However, let’s get more specific on their locale.

In Europe, these beautiful winged insects thrive across several countries. Sweden and Great Britain are two notable examples. It’s interesting to note, the largest vibrant population of Large Blue butterflies exists in Great Britain.

Venturing further, in Asia, these creatures are found in particular regions of Russia, Kazakhstan, and Mongolia. Similarly, in North America, they are spotted in some areas of Canada and the United States.

Nowadays, the distribution of Large Blue is not as extensive as in the past. Changes in their inhabitat due to human activity is a significant factor.

Despite the reduced range, you’ll still see these winged beauties fluttering around in nature reserves and certain grassland areas across the continents, painting a picture of natural vitality and biodiversity.

Remember, when they are not soaring the skies, they cluster in pockets around specific host plants, creating a spectacle for the eyes and nurturing hopes for their conservation.

What are the Main Characteristics of the Large Blue?

The Large Blue (Phengaris arion) is a spectacular butterfly, renowned for its striking appearance. Boasting a wingspan of approximately 2 inches (around 5 cm), it easily stands out amongst its brethren.

Its primary defining feature, as the name suggests, is the vibrant blue hue of its upper wings. But note, this is typically more visible in males than females.

  • The Upper Side of these wings is adorned with black margins and dotted with black spots, creating a contrasting pattern that’s fairly distinguishable. This pattern extends to the underwing, which, unlike the upper wing, bears a more muted color palette. It consists of pale blues, browns, and whites patterned with intricate spots and markings, exuding a camouflage-like appearance.
  • As for their body morphology, Large Blues possess a fairly typical butterfly structure. They are equipped with medium-sized antennae adorned with white and black rings, and their bodies are black with a slight hint of blue, maintaining the consistency of their blue theme.
  • In comparison, the Flight Pattern of a Large Blue is swift and determined, often low to the ground. They are particularly active on sunny days, fluttering around the host plants and displaying their vibrant hues for all to admire.

In summary, the Large Blue’s combination of striking coloration, unique patterning, and swift flight makes it a distinctive yet mesmerizing sight within the insect realm.

How to Identify Male and Female Large Blue?

Identifying the gender of the Large Blue butterfly is a task you can certainly achieve with the right knowledge.

Identifying Male Large Blue

Male Large Blues are identifiable by their vibranctic, unique blue coloration which extends across their wings. This is their most striking feature and the one which gives them their name.

On the upper side, males are unmistakeable, having broader and less ragged borders than females.

  • Color: The color of a male is an intense, bright blue.
  • Outline: The male has a more streamlined and oval shape.
  • Size: Males tend to be slightly smaller, with a wingspan of around 1.5 inches (38 mm).

Identifying Female Large Blue

Females of the Large Blue species are a bit more challenging to identify, as they lack some of the vibrant blue of the males.

Their coloration is primarily a grey or brown on the upper side, with blue limited to the bases of the wings. They also have broad, dark borders.

  • Color: The females are more brown or grey with blue at the base of their wings.
  • Outline: They have rounder wings, and their markings are more prominent.
  • Size: Females are generally larger, with a wingspan that could extend up to 2 inches (50 mm).

The main differences lie in color, wing shape, and size. With these cues in mind, you will be adept at differentiating between male and female Large Blues.

What is the Mating Ritual of Large Blue?

The mating ritual of the Large Blue is a fascinating process. Males of the species typically emerge earlier than females, allowing them to establish territories around the grasslands they inhabit.

These sites, usually chosen for good exposure to the sun, are meticulously guarded against rival males.

When a female enters his territory, the male will initiate a courtship display. He will undertake a flight pattern around her to catch her attention, often accompanied by a fluttering distinctive to his wings. This delicate dance continues until the female signals her acceptance of the male.

The process doesn’t end here. Once accepted, the male will then proceed to mount the female, effectively initiating copulation.

This aspect of mating can last up to 45 minutes, after which they disengage and fly off separately. The female then stores the sperm until it’s time to fertilize her eggs.

Take note of this: Patroller males do not stake out territories. Instead, they fly around seeking out receptive females, offering a different form of mating strategy within the Large Blue butterfly species.

The mating ritual of the Large Blue, as you’ve read, is an intricate dance of displaying, accepting, and mating behavior. It’s no less than an elegant symphony of nature!

What Does the Caterpillar of Large Blue Look Like?

The caterpillar of the Large Blue butterfly, also known scientifically as Phengaris arion, is distinctly recognizable.

With a vibrant, luminescent green body, the caterpillar is an enchanting sight. Like most caterpillars, the Large Blue’s offspring is soft and seemingly delicate.

The Large Blue caterpillar has several fascinating features. For one, it boasts tiny, white hairs running along the sides of its immaculate body—an intriguing detail, signifying its species.

Additionally, it has a series of yellow lines forming stripes that intersect right along the dorsal line. Its size is nothing to scoff at either, reaching an impressive 12 millimeters (about 0.47 inches) in length at its final instar.

Can you guess the unique feature that sets it apart? This caterpillar bears a honey gland, a special organ used to produce sweet secretions.

These secretions attract ants and initiate a surreal survival interaction, where it essentially tricks ants into providing protection.

Even though it seems unremarkable at first glance, the Large Blue caterpillar is an extraordinary creature with unique features that make it a standout among caterpillars.

What is the Life Cycle of Large Blue?

The life cycle of the Large Blue can be aptly described as ‘perplexing’. It’s divided into four main stages; these are egglarvapupa, and adult.

The peculiar nature of such sequence lies in the detail of its progression.

The Large Blue’s life cycle initiates with an egg. Female Large Blues lay their eggs on Thymus vulgaris (commonly known as thyme) or Origanum vulgare (also known as oregano). The egg stage lasts for about a week.

Transitioning to the larva stage, this is where things get quite interesting. The larva – or caterpillar -increases in size for about three weeks, then engages in a rather unorthodox behavior.

It falls to the ground and secretes sweet substances that attract red ants. The ants, beguiled by the sweet secretion, carry the caterpillar back to their nest.

Living amongst the ants, the Large Blue caterpillar turns predator. It feeds on ant grubs during its time underground, which can last for about 10 months.

After this, a pupa emerges, which then stays in the ant nest for another two weeks.

Finally, the glorious transformation culminates in the adult butterfly. This final stage lasts for about five days, signifying the completion of the Large Blue’s unique life cycle.

During this period, adult butterflies feed, mate and lay eggs – setting the cycle into motion once again.

What Is the Average Life Expectancy of a Large Blue?

You might be surprised to learn that the Large Blue butterfly doesn’t hold a lengthy life expectancy. In fact, as an adult, their life spans a mere 4-5 days, or up to a week under optimal conditions.

However, this brevity isn’t unusual among butterflies, especially given their environmental vulnerabilities and delicate physiological constitution.

  1. Egg Stage: The first step of life for a Large Blue begins as an egg, a period lasting for about a week.
  2. Larval Stage: This stage is far lengthier. The larva, or caterpillar, grows over a span of 3 weeks.
  3. Pupal Stage: The pupal stage, where the insect undergoes metamorphosis, lasts nearly 9 months. During this time, they’re immobile and encased within a cocoon.
  4. Adult Stage: Finally, the transformed butterfly emerges. However, their flight is regrettably short-lived, with life expectancy ranging between 4 to 7 days.

These stages constitute the annual life cycle of the Large Blue butterfly. Quite evidently, its adult life is brief with the majority time spent in eggs, larval, and pupal stages.

This strategy signifies emphasis on long-term survivorship in the early developmental stages.

The short-lived adult phase is primarily meant for reproduction, to ensure the continuation of the species in the coming generation.

What Does the Diet of a Large Blue Consist Of?

A large blue butterfly primary source of nutrition comes from nectar. The primary source of nutrition for adult butterflies, nectar offers a wealth of sugars, minerals, and other nutrients.

Various flowering plants such as thistles, knapweeds, and marjoram serve as natural ‘nectar cafes’ for them.

Caterpillars: The dietary requirements of large blue caterpillars are more specific. In their earliest stages, they feed on the flower buds of the wild thyme or marjoram plants; however, once they reach their fourth instar, their diet switches entirely to the larvae of a specific species of red ants (Myrmica sabuleti).

Ant larvae: Yes, you read that right. Large blue caterpillars are known for their unique ‘ant-dependent’ lifestyle. Their later stages (after the 4th instar) would be spent entirely within an ant nest, feeding on the ant grubs.

They achieve this by producing chemical and acoustic signals that imitate the ants’ own, convincing the ants that the caterpillar is one of their own, a behavior known as ‘aggressive mimicry’ or ‘chemical camouflage.’

So, while adults savor the sweet nectar of flowers, the caterpillars of this fascinating species practice a degree of subterfuge to secure the ant larvae meal.

The diet of a large blue is indeed fascinating and demonstrates the insect’s incredible adaptability and survival strategies in the wild.

Which Plants Serve as the Primary Hosts for Large Blue?

One significant aspect of the Large Blue’s survival and propagation is its reliance on particular host plants. These specific plants become pivotal to the butterfly at its caterpillar stage.

Large Blues primarily prefer Thymus drucei and Origanum vulgare, species of Wild Thyme and Marjoram, respectively.

The female Large Blue lays its eggs on the bud base of a flower. When the caterpillar hatches, it feeds voraciously on the flower heads for up to 4 weeks.

It’s then the Thymus drucei and Origanum vulgare plants these caterpillars prefer to call home.

They’re not just hosts for feeding, but they’re also strategic locations for the next phase of the Large Blue lifecycle. After dropping to the ground from the host plant, the caterpillar’s next destination is an ant nest.

This strategy only works if the ants belong to the Myrmica species. If the host plant is growing over an ant nest from this same species, the Large Blue’s survival rate increases greatly.

Boldly put, the intertwined lives of the Large Blue butterfly, the Thymus drucei and Origanum vulgare plants, and the ants from the Myrmica species, is a fantastic showcase of natural symbiosis.

Large Blues’ existence heavily depends on the balance of this ecology, making the presence of these specific plants critical as primary hosts.

What are the Unique Mimicry Behaviors in Large Blue?

The Large Blue butterfly employs impeccable mimicry as an integral part of its survival mechanism, showcasing the marvels of nature.

One of the behavior that sets it apart is its caterpillars’ ability to mimic ant larvae. This cunning act confuses the ant colonies, which inadvertently offer protection to the Large Blue caterpillars, mistaking them for their own brood.

Moreover, the caterpillars further manipulate the ants using chemical signals also known as pheromones. This chemical deception lures the worker ants to carry the caterpillar back into the ant nest.

Once within the safety of the nest, the clever mimicry continues as the caterpillar makes sounds mimicking the queen ant. This auditory mimicry placates the ant defenses, leading them to ignore the caterpillar, even when it feeds on the ant larvae.

Observably, this unique relationship between the Large Blue caterpillar and ants, called myrmecophily, is a testament of the intricacies of evolution.

Combining both chemical and acoustic mimicry, the Large Blue has carved a niche in an otherwise hostile environment, demonstrating the lengths to which nature will evolve for survival.

In essence, the Large Blue’s refined mimicry behaviors highlight not just its survival strategy, but also the complex and interactive relationships present in the ecosystem.

The butterfly’s survival hinges on mimicking potential predators, showcasing a fascinating example of nature’s crafty work around challenges. Rare and intriguing, it clearly stands as a wonder among butterflies.

What Are the Main Threats to Large Blue Populations?

The Large Blue butterfly, prevalent in western Europe, is a species that has been on a steady decline. As its grassland habitat diminishes, the butterfly’s numbers are dwindling, leading to its status as an endangered species. Let’s dive into the main threats it faces:

  • Habitat Loss

The principle threat faced by the Large Blue is habitat loss. In fact, the sudden decline in numbers in the last century was primarily associated with the destruction of its natural environment. Human-made interventions, such as intensification of agriculture and urbanization, have resulted in the destruction of the Large Blue’s habitat.

  • Climate Change

Climate change, with its increasing temperatures and extreme weather events, poses a significant threat. Changes in weather patterns disrupt the delicate balance of the ecosystem. For the Large Blue, the shifted seasons cause mismatches in the timing of its life cycle stages.

  • Reduction in Host Ants

The Large Blue butterfly has a unique and intricate relationship with a specific type of ant. In its caterpillar stage, it relies heavily on this ant for survival. Reductions in these ants’ colonies due to changes in land use and insecticides have adverse effects on the butterfly’s population.

  • Inadequate Management of Reserves

The butterfly’s habitat requires certain conditions, including a specific type of grazing. Inadequate management of these reserves, through incorrect frequency or intensity of grazing, can disrupt the ecosystem to the detriment of the Large Blue.

To save this fascinating creature, these threats need to be effectively mitigated. Conservation actions, including proper management of reserves, reducing insecticide use and restoring natural habitats, can help restore the Large Blue population to its former glory.


Now that you know more about the Large Blue, its fascinating life cycle, intricate behavior, and the threats it faces, you’re better equipped to identify and protect this incredible butterfly.

The delicate balance of the Large Blue’s ecosystem relies on our understanding and respect.

Do leave a comment about your own experiences with the Large Blue, or any thoughts you may have on its preservation!

Butterflies   Updated: July 8, 2023
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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