Blue Milkweed Beetle: All You Need to Know in a Nutshell

The blue milkweed beetle is an intriguing insect that thrives on milkweed plants. They play an essential role in the ecosystem by helping control the milkweed population, while also being a source of food for other creatures.

Belonging to the Chrysomelidae family, blue milkweed beetles are among a variety of insects attracted to milkweeds. Some of their fellow milkweed visitors include the large milkweed bug, common milkweed bug, and red milkweed beetle found in Wisconsin.

As you explore the world of blue milkweed beetles, be prepared to learn about their fascinating features, life cycle, and interactions within the plant communities they inhabit. Understanding the role of these beetles in nature can help us appreciate their importance in maintaining a balanced ecosystem.

Blue Milkweed Beetle Overview

Scientific Classification

The Blue Milkweed Beetle (Chrysochus cobaltinus) is a vibrant, metallic blue insect classified under:

• Order: Coleoptera
• Family: Chrysomelidae

Distribution and Habitat

These beetles are native to North America, and their distribution ranges from:

• Western United States: California
• Canada: British Columbia
• Central America

The Blue Milkweed Beetle prefers habitats containing milkweed plants, on which they feed and lay eggs.

Note: If you find more information on the Blue Milkweed Beetle, please edit this article accordingly.

Life Cycle and Reproduction

Eggs

Blue milkweed beetles start their life cycle as eggs. Females lay these small, oval-shaped eggs on milkweed plants. Examples of cardiac glycosides-rich plants include milkweed and oleander. Each female can deposit numerous eggs, as they are known to be polyandrous.

Larvae

The eggs hatch into larvae, which are commonly called grubs. These white, segmented larvae have a distinct brown head. The stage of a beetle larva is divided into several instars or growth stages. As larvae, they consume milkweed leaves, increasing in size with each molt.

Pupa

After reaching the final larval stage, the grubs transition into the pupa stage. During this time, they remain inactive inside a brown, protective cocoon-like structure. Overwintering often occurs in the pupa stage, meaning the beetle development slows down to survive the colder months.

Adult Beetles

As adults, blue milkweed beetles emerge from their pupa stage, featuring a metallic blue or green coloration. They continue to feed on milkweed plants, acquiring cardiac glycosides, which provide them with a defense against predators.

Here’s a comparison table highlighting the differences in blue milkweed beetle life stages:

During the adult stage, mate guarding is a common behavior among blue milkweed beetles. Males protect their female partners from other potential mates, ensuring their offspring’s success.

In summary, the life cycle and reproduction of blue milkweed beetles are characterized by four main stages: eggs, larvae, pupa, and adult beetles. Their preference for milkweed plants, as well as their polyandrous behavior, are key factors in their survival and reproduction.

Physical Characteristics

Coloration and Patterns

The blue milkweed beetle, also known as the cobalt milkweed beetle, displays a vibrant orange color contrasted by lucent gray wings. Additionally, black patches are visible on its body, contributing to its striking appearance.

Dome-Shaped Body

One notable feature of the blue milkweed beetle is its dome-shaped body. This unique body shape sets it apart from other beetles and makes it easily identifiable in the wild.

Elytra

The elytra, or hardened forewings, of the blue milkweed beetle provide protection for its delicate wings and body. These elytra are marked with distinctive patterns that make the beetle more recognizable.

• Some key features of the blue milkweed beetle include:
  • Orange coloration
  • Lucent gray wings
  • Black patches
  • Dome-shaped body
  • Elytra with unique patterns
  • Clubbed antenna

In comparison, the cobalt milkweed beetle shares similar features with the blue milkweed beetle, such as the striking orange coloration and clubbed antenna. However, the cobalt milkweed beetle has a slightly different appearance due to variations in wing color and pattern.

Behavior and Ecology

Feeding Habits

The blue milkweed beetle feeds on various parts of the milkweed plant, such as:

• Leaves
• Flowers
• Seed pods

These beetles are herbivores and consume milkweed plants (Asclepias spp.) as their main food source.

Relationship with Milkweed Plants

Blue milkweed beetles have developed a close relationship with milkweed plants. They rely on these plants for sustenance and help in their survival. Milkweed plants are known for their latex, which can be toxic to some insects, but blue milkweed beetles have adapted to tolerate it.

Defenses and Predators

Their bright blue coloration is a warning signal to potential predators. This is an example of aposematism, a form of warning coloration that serves to deter predators. Blue milkweed beetles also sequester toxins from the milkweed plants they consume, making them unpalatable to predators.

Interactions with Other Insects

Blue milkweed beetles share their host plants with other insects such as:

• Monarch butterflies
• Large and small milkweed bugs
• Milkweed tussock moths

These insects may compete for the same resources, like milkweed leaves and flowers, but they usually coexist on the same plants. Overall, these species form a community of milkweed-associated insects that rely on Asclepias plants for survival.

Here’s a comparison table of some different milkweed insects:

Milkweed Bug Comparison

Large Milkweed Bug

The large milkweed bug (Oncopeltus fasciatus) belongs to the order Hemiptera and the family Lygaeidae. These bugs:

• Measure about ¾” long
• Have orange to reddish-orange color with a black band across their back
• Feed mainly on milkweed seeds
• Are commonly found on milkweed plants

Nymphs and adult of the large milkweed bug feed on milkweed, especially the seeds.

Small Milkweed Bug

Small milkweed bugs also belong to the order Hemiptera. Their characteristics include:

• Smaller size than the large milkweed bugs
• Similar appearance and coloration

Comparatively, small milkweed bugs are less frequently encountered on milkweed plants.

Red Milkweed Beetle

Red milkweed beetle (Tetraopes tetrophthalmus) is a longhorn beetle found on milkweed:

• Member of the Cerambycidae family
• Prevalent in the eastern United States
• Has a bright red and black appearance
• Specializes in a particular milkweed species

There are 26 different milkweed longhorn beetles, and each prefers a different species of milkweed.

Swamp Milkweed Leaf Beetle

The swamp milkweed leaf beetle (Labidomera clivicollis) is another beetle found on milkweed plants. Key features of this beetle include:

• A vivid yellow and black pattern
• Feeds on various milkweed species, including swamp milkweed

Swamp milkweed leaf beetles also belong to the order Coleoptera.

Others

Numerous other insects are attracted to milkweed plants, including bees and butterflies like the monarch.

Damage and Control

Impact on Milkweed Plants

Blue milkweed beetles, along with other insects like milkweed bugs and oleander aphids, are milkweed specialists, meaning they feed specifically on milkweed plants. They can cause considerable damage to the foliage and stems, affecting the plant’s health. Some impacts include:

• Leaves may become skeletonized
• Foliage may wilt and turn yellow

These insects also feed on the plant’s toxic compounds, making them poisonous to potential predators and deferring them from eating the beetle.

Control Methods

To control the infestation of blue milkweed beetles and other milkweed pests, various methods can be employed. Some examples include:

• Removing leaf litter: Leaf litter can provide a habitat for overwintering insects. Clearing it away can help reduce pest populations.
• Manual Removal: Handpick milkweed bugs, aphids, and beetles from plants and dispose of them appropriately.
• Biological Control: Introducing natural predators, such as wasps, can help keep insect populations in check.
• Restricting Dogbane: Dogbane, a close relative of milkweed, can serve as an alternate host for pests. Removing these plants can help reduce infestations.

It’s essential to strike a balance between pest control and respecting the milkweed plant’s role in the ecosystem. Milkweed is crucial for many insects, including monarch butterflies and various other milkweed specialists, contributing to protecting these species while managing the damage they cause.

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Blue Milkweed Beetles Mating

Blue Beetle ID
Location: central California
June 1, 2011 1:32 pm
Hello Bugman,
Can you help me in identifying these beetles? Sure are eye-catching.
Thank you very much.
Signature: Dak

Hi Dak,
These distinctive beetles are called Blue Milkweed Beetles, Chrysochus cobaltinus, and we are quite pleased that you captured one pair in the act of mating.

Hello Daniel,
Thank you for your quick ID and for maintaining such a interesting site!
Dak

Letter 2 – Blue Milkweed Beetles in Westridge-Canyonback Wilderness Park

Subject:  Blue Milkweed Beetles
Geographic location of the bug: Westridge-Canyonback Wilderness Park, California
Date: 06/04/2021
Time: 9:25 AM PDT
Your letter to the bugman:  Dear Readers,
Daniel was out hiking near the Getty Museam in a Santa Monica Mountains Conservancy park when he pointed out the Narrow-Leaf Milkweed that was just beginning to bloom to his hiking partners Naeemah and Sharon.  Some plants had numerous Blue Milkweed Beetles feeding on the leaves.  According to BugGuide:  “Larvae are obligate root feeders, and adults eat the leaves of larval host plants. Females are highly polyandrous, males engage in extended periods of post-copulatory mate guarding.”

Milkweed is a very popular plant with many pollinating insects including butterflies, bees and wasps. so many years ago we created a Milkweed Meadow tag for the complex ecosystem that is associated with milkweed.

Update:  June 19, 2021  Mating Blue Milkweed Beetles
This weekend while hiking at the same location with Sharon and Melanie, Daniel spotted a solitary pair of mating Blue Milkweed Beetles.  He managed to get one image before the presumably male Blue Milkweed Beetle dropped to the ground.  Daniel felt somewhat guilty that his voyeurism led to coitus interruptus.

Letter 3 – Cobalt Milkweed Beetle

please verify
August 10, 2009
I found these beetles on milkweed and have tentatively identified them as Blue Milkweed Beetles. Is that your assessment too? And is that the beetles’ genitalia that I am seeing in the second photograph?
Tom
near Mt Shasta, Ca

Dear Tom,
BugGuide refers to Chrysochus cobaltinus as the Cobalt Milkweed Beetle.  Your photo of a couple in the process of mating is a nice addition to our Bug Love pages.  We will try to get an answer on the genitalia question for you.

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Blue Milkweed Beetles Mating

Blue Beetle ID
Location: central California
June 1, 2011 1:32 pm
Hello Bugman,
Can you help me in identifying these beetles? Sure are eye-catching.
Thank you very much.
Signature: Dak

Hi Dak,
These distinctive beetles are called Blue Milkweed Beetles, Chrysochus cobaltinus, and we are quite pleased that you captured one pair in the act of mating.

Hello Daniel,
Thank you for your quick ID and for maintaining such a interesting site!
Dak

Letter 2 – Blue Milkweed Beetles in Westridge-Canyonback Wilderness Park

Subject:  Blue Milkweed Beetles
Geographic location of the bug: Westridge-Canyonback Wilderness Park, California
Date: 06/04/2021
Time: 9:25 AM PDT
Your letter to the bugman:  Dear Readers,
Daniel was out hiking near the Getty Museam in a Santa Monica Mountains Conservancy park when he pointed out the Narrow-Leaf Milkweed that was just beginning to bloom to his hiking partners Naeemah and Sharon.  Some plants had numerous Blue Milkweed Beetles feeding on the leaves.  According to BugGuide:  “Larvae are obligate root feeders, and adults eat the leaves of larval host plants. Females are highly polyandrous, males engage in extended periods of post-copulatory mate guarding.”

Milkweed is a very popular plant with many pollinating insects including butterflies, bees and wasps. so many years ago we created a Milkweed Meadow tag for the complex ecosystem that is associated with milkweed.

Update:  June 19, 2021  Mating Blue Milkweed Beetles
This weekend while hiking at the same location with Sharon and Melanie, Daniel spotted a solitary pair of mating Blue Milkweed Beetles.  He managed to get one image before the presumably male Blue Milkweed Beetle dropped to the ground.  Daniel felt somewhat guilty that his voyeurism led to coitus interruptus.

Letter 3 – Cobalt Milkweed Beetle

please verify
August 10, 2009
I found these beetles on milkweed and have tentatively identified them as Blue Milkweed Beetles. Is that your assessment too? And is that the beetles’ genitalia that I am seeing in the second photograph?
Tom
near Mt Shasta, Ca

Dear Tom,
BugGuide refers to Chrysochus cobaltinus as the Cobalt Milkweed Beetle.  Your photo of a couple in the process of mating is a nice addition to our Bug Love pages.  We will try to get an answer on the genitalia question for you.

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.