What makes a beetle’s metallic shine?

Tiny structures that reflect light

Bronze Beetle

Chrysolina bankii

The bronze beetle (Chrysolina bankii) is a metallic bronze leaf beetle, 8–10.7 mm long, with orange-brown to dark brown legs. It is native to western Europe, from southern England to Italy and Iberia, and to north-west Africa, the Canary Islands and Madeira, and it has been introduced to California. For its genus it eats an unusually wide range of plants, from ribwort plantain and mints to thistles and rosemary.

Also known as Chrysolina banksi, Chrysolina banksii

Bronze beetle abilities

3 ways beetles make metallic colour
Its shell gleams bronze, copper or greenish depending on the light. In beetles, shine like this is made by structure, not paint.
- Scientists group beetle shine into three kinds: stacked thin layers (multilayer reflectors), crystal-like 3D patterns and fine ridges called diffraction gratings.
- Beetles are sometimes called “living jewels” because of these effects.
- No one has yet measured the bronze beetle’s shell, so which kind it uses is not known.
Sources [3]
5 plant families eaten
Most Chrysolina beetles stick to one plant family. The bronze beetle eats from five.
- It eats plants from nine genera of the mint family, plus plantains and some daisy-family, buttercup-family and dock-family plants.
- In Britain it is found especially on ribwort plantain and on mints and their relatives.
- Rosemary and Dittrichia viscosa were added to the list in 2020, and both were confirmed in the lab.
Plant families eaten
Bronze beetle5
Most Chrysolina species1 (less often 2)
From a 2020 review of its food plants.
Sources [2, 6]
Self-made defence chemicals (genus)Still debated
Chrysolina leaf beetles give off defensive fluids. Whether the bronze beetle does the same has not been tested.
- Defensive fluids of Chrysolina beetles contain cardenolides (cardiac glycosides), chemicals that affect the heart.
- A 1977 study found that the beetles make these chemicals themselves instead of collecting them from their food plants.
- Other leaf beetles in the same subfamily borrow defence chemicals from their host plants instead.
- In some of those relatives, the larvae push out little glands on their backs and release defensive fluid when disturbed.
Sources [4, 11, 12]
45× body weight held (rosemary beetle)
Hairy pads on its feet let it climb leaves and hang on underneath.
- Chrysolina beetles have hairy adhesive pads on their feet. On waxy leaves, wax sticks to the hairs and grip drops sharply.
- In the rosemary beetle, males have special disc-tipped hairs. Clinging to a female’s back, they held about 45 times their own body weight, females about 30 times.
- No one has measured the bronze beetle’s grip yet.
Sources [7, 8]
Freeze a defence many insects useStill debated
When touched, many beetles drop from their plant and lie still. It is often said that the bronze beetle does this too, but it has not been studied.
- Playing dead (thanatosis) usually happens after a predator has already touched its prey.
- Scientists think it can stop a predator from attacking further.
- We found no study of this behaviour in the bronze beetle.
Sources [13]
Larva usual winter stage in Britain
In Britain it usually gets through the winter as a larva. In warmer places adults keep going too.
- Records peak twice a year: in April and May, and again from September to November.
- Few are recorded in July and August. Why has not been studied for this species.
- In Britain, September and October have the most records of all.
Records in four months
May (peak)2,937
October2,581
January303
August285
Worldwide records on GBIF by month, October 2026.
Sources [2, 14]
Unknown flight abilityStill debated
Under the wing cases sit folded flight wings. Whether the bronze beetle uses them is not known.
- Most beetles have hard front wings (elytra) with the hind wings folded beneath.
- California’s plant-health officials say it “presumably can fly”, but we found no record of it flying.
- Losing flight has happened again and again in insects. Some Chrysolina species cannot fly, and experts disagree about whether the rosemary beetle can.
Sources [1, 5, 15]

Tap a pin on the model or a part below.

Bronze metallic wing cases
- The wing cases (elytra) are the beetle’s hardened front wings. The thin flight wings fold away underneath them.
- They are metallic bronze, dotted with small pits scattered at random.
- In shiny beetles, metallic colour is made by tiny structures in the shell that reflect light, not by metal-coloured pigment.
Sources [1, 2, 3]
- The shield behind the head (the pronotum) is the same metallic bronze as the wing cases.
- Chrysolina leaf beetles give off defensive fluids containing chemicals called cardenolides, which they make themselves rather than taking from their food plants.
- These chemicals have not been tested in the bronze beetle itself.
Sources [2, 4]
Unknown can it fly?
- Most beetles fold their hind wings away under the wing cases.
- Whether the bronze beetle flies is not well recorded. California’s plant-health officials say it “presumably can fly”.
- Some relatives, such as Chrysolina sulcicollis and Chrysolina virgata, cannot fly at all.
Sources [1, 5]
5 plant families eaten
- Adults and larvae both chew leaves.
- Its food plants come from five families: the mint family (nine genera), plantains, the daisy family, the buttercup family and the dock family.
- In Britain it is found especially on ribwort plantain and mint-family plants, including mints.
Sources [2, 6]
Orange-brown leg colour
- Its legs are orange-brown to dark brown.
- Chrysolina feet have pads of tiny hairs that cling to leaves. Waxy leaf surfaces make them slip.
- In the rosemary beetle, a close relative, a male clinging to a female’s back holds on with about 45 times his own body weight.
Sources [2, 7, 8]
- Its gut copes with leaves from very different plants, from mints to thistles.
- In a relative, the mint beetle Chrysolina herbacea, gut bacteria help the beetle deal with the strong-smelling chemicals of watermint.
- No one has studied the bronze beetle’s gut bacteria yet.
Sources [6, 9]
2 new food plants found in 2020
- In 2020 a leaf-beetle expert reported two new food plants on Mallorca: rosemary, and the sticky yellow-flowered shrub Dittrichia viscosa.
- Earlier records include milk thistle, cardoon, artichoke and a wild sage, Salvia verbenaca.
- Rosemary is a common garden plant in California, one reason officials there think the beetle could spread widely.
Sources [5, 6]
Larva usual winter stage in Britain
- In Britain the bronze beetle usually spends the winter as a larva. In warmer places, adults are found in winter too.
- In many leaf beetles, such as the Colorado potato beetle, the fully grown larva burrows into the soil to become a pupa.
- Where and how the bronze beetle pupates has not been described in detail.
Sources [2, 10]

Real bronze beetles

Photos from Wikimedia Commons. Two show its relative, the rosemary beetle, and can repaint the 3D model.

Adult bronze beetleOval and domed, 8–10.7 mm long, metallic bronze all over with orange-brown to dark brown legs.Usually near the coast in Britain; very common in south-west EuropeCéret, in the French Pyrenees, May 2019. Photo: Fabricio Cardenas, CC BY-SA 4.0
Feeding on a plantain leaf, Alicante, SpainPhoto: Katja Schulz, CC BY 2.0
Els Poblets, Alicante, SpainPhoto: Katja Schulz, CC BY 2.0
Out and about in FebruaryPhoto: liesvanrompaey, CC BY 2.0
In Spanish it is called crisomélido de BankPhoto: jacilluch, CC BY-SA 2.0
Jimena, Andalucía, SpainPhoto: gailhampshire, CC BY 2.0
Rosemary beetle (Chrysolina americana)Smaller, 6–7 mm, with metallic purple and green stripes on its wing cases and thorax.A garden pest of rosemary, lavender, sage and thymeIts relative the rosemary beetle. Photo: Iurie Nistor, CC BY-SA 4.0
Rosemary beetle (Chrysolina americana)Smaller, 6–7 mm, with metallic purple and green stripes on its wing cases and thorax.A garden pest of rosemary, lavender, sage and thymeRosemary beetle, Aragon, Spain. Photo: S. Rae, CC BY 2.0

Bronze beetle by the numbers

Measured by scientists, recording schemes and plant-health officials, with comparisons you can picture.

Length: 8–10.7 mm; adult beetle; Bronze beetle10.7 mmRosemary beetle7 mm; Up to about 1½ times as long as a rosemary beetle⁠[2, 16]
Plant families eaten: 5; mint, plantain, daisy, buttercup and dock families; Most Chrysolina species eat from just 1⁠[6]
Mint-family genera eaten: 9; genera of the Lamiaceae⁠[6]
Species in its genus: 400+; Chrysolina, split into 65 subgenera⁠[17, 18]
Leaf beetle species: 36,000+; family Chrysomelidae, worldwide⁠[19]
GBIF records: 14,927; from 17 countries, checked October 2026⁠[14]
Busiest month: May; 2,937 GBIF records; October is next with 2,581⁠[14]
California counties: 5; where it was established by 2022⁠[5]
Earliest US record: 2008; research-grade iNaturalist photo, UC Berkeley campus⁠[20]
Year named: 1775; described by Johan Christian Fabricius⁠[14]

Bronze beetle myths and facts

Some popular bronze beetle claims hold up. Others don’t, or have never been tested.

0 of 8 answered

“Bronze beetles only eat mint.”
“A beetle’s metallic shine comes from metal-coloured pigment.”
“Bronze beetles are dangerous garden pests.”
“When disturbed, a bronze beetle drops and plays dead.”
“Every beetle with wings can fly.”
“Leaf beetles have been used to fight weeds.”
“The rosemary beetle, Chrysolina americana, comes from America.”
“The bronze beetle is an endangered species.”

Bronze beetle records

Record-breakers from the bronze beetle and its leaf beetle family.

One of the widest menus in its genus
5 plant families
Bronze beetle
most Chrysolina species stick to one family, less often two⁠[6]
A giant family
36,000+ species
Leaf beetles (Chrysomelidae)
plant-eating beetles found worldwide⁠[19]
A big genus
400+ species
Chrysolina
sorted into 65 subgenera⁠[17, 18]
Weed-busting relative
St John’s wort
Chrysolina quadrigemina
successfully controlled this invasive weed in California⁠[21]
Super grip
≈45× body weight
Rosemary beetle (male)
grip on a female’s wing cases, measured in a lab⁠[8]
Most records
4,189 records
Spain
of 14,927 on GBIF; France is next with 3,525⁠[14]

A bronze beetle’s life

From egg to shiny adult. Some stages are still poorly known for this species.

Egg
A little-known start
Little has been published about this species’ eggs. Related leaf beetles, such as the Colorado potato beetle, lay small clusters of yellow-orange eggs under leaves.⁠[10]
Larva
A leaf-chewing grub
Larvae chew leaves like the adults. On Mallorca, a few were found feeding on the sticky shrub Dittrichia viscosa, and they ate it in the lab too.⁠[6]
Winter
Winter as a grub
In Britain it usually spends the winter as a larva. In warmer places, adults are found in winter too.⁠[2]
Pupa
A change underground?
In many leaf beetles the fully grown larva burrows into the soil to become a pupa. This has not been described in detail for the bronze beetle.⁠[10]
Spring
Spring peak
Records climb in April and peak in May, with 2,937 GBIF records in that month.⁠[14]
Summer
A quiet summer
Few are recorded in July and August. Why has not been studied for this species.⁠[14]
Autumn
Second peak
Records rise again from September to November. In Britain, September and October are the busiest months.⁠[14]
Adult
Finding a mate
Adults, sometimes in mating pairs, have been found on rosemary bushes.⁠[6]

Bronze beetle vs Colorado potato beetle vs rosemary beetle

Three leaf beetles, three very different reputations.

Bronze beetle vs Colorado potato beetle vs rosemary beetle
	Bronze beetle	Colorado potato beetle	Rosemary beetle
Scientific name⁠[14, 10, 16]	Chrysolina bankii	Leptinotarsa decemlineata	Chrysolina americana
Length⁠[2, 10, 16]	8–10.7 mm	about 10 mm (3/8 inch)	6–7 mm
Colours⁠[2, 10, 16]	Metallic bronze, orange-brown legs	Yellowish-white wing cases with 10 black stripes	Metallic purple and green stripes
Main food⁠[2, 6, 10, 16]	Plantains, mints and other mint-family plants, some thistles	Potato, eggplant, tomatillo	Rosemary, lavender, sage, thyme
Pest?⁠[5, 10, 25, 16]	Not known to be a pest	Major potato pest that quickly evolves resistance to insecticides	Garden pest of herbs
Winter⁠[2, 10, 16]	Usually as a larva (Britain)	Adults 13–25 cm underground	Adults present all year

The bronze beetle and the rosemary beetle are in the same genus, Chrysolina.

Is the bronze beetle endangered?

No. It has never been assessed by the IUCN, but it is described as very common.

IUCN Red List

Not Evaluated (NE)

Trend unknown

A leaf-beetle expert calls it very common. In Britain it is widespread in the south-west, usually near the coast, and can be locally common.⁠[14, 24, 6, 2]

Not evaluated by the IUCN Red List (checked October 2026).

Threats

Threats not studied
We found no study of threats to the bronze beetle. Nobody has measured whether its numbers are rising or falling.⁠[14]
Moved by people
Beetles can travel with plants. California has intercepted it on plant material from Texas and in parcels from Oregon. Officials say it might have effects on native plants that nobody has spotted yet.⁠[5]

What’s helping

Recording it15,429
Photos on iNaturalist and records sent to UK Beetle Recording show where it lives and when it is active.⁠[20, 2]
Watching the newcomers
California’s plant-health officials track where it turns up. In 2022 it was known from five counties.⁠[5]

Bronze beetle quiz

12 questions. Every answer is somewhere on this page.

Question 1 of 12Score 0

How long is an adult bronze beetle?

Bronze Beetle field notes

Diet, food web, safety and badges from the Snappit field guide.

Diet & Feeding

These beetles are plant-eaters. Adults and larvae chew the leaves of many plants, such as ribwort plantain, mints and thistles.

Primary Foods

Plantago lanceolata
Mentha spicata
Silybum marianum
Lamiaceae plants
Foraging Method: Foraging

Age differences: Larvae and adults both feed on the leaves of their host plants.

Ecological connections

Great TitEaten by
Adult beetles are a food source for insectivorous birds.
Garden Cross SpiderEaten by
Spiders can capture adult beetles in their webs.
SpearmintEats
The beetles feed on the leaves of spearmint plants.
Ribwort PlantainEats
In Britain the beetles are found especially on ribwort plantain.

Safety

Danger 1/5 · Very low

Watch beetles on their plants and do not pick them up. They are easily hurt, and leaf beetles can give off defensive fluids. If you touch one, wash your hands.

Traits

Collections

Insects

Classification

Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Coleoptera
Family: Chrysomelidae
Genus: Chrysolina

Sources for these bronze beetle facts

25 studies and references · checked Oct 16, 2026

Frequently Asked Questions

How to identify Bronze Beetle?

Look for hard wing covers meeting in a line down the back, then compare the antennae, body shape, legs and markings. Metallic colors shift a lot with lighting. Beetle Identifier: upload a photo and compare the visible details.

How big is Bronze Beetle?

8-10.7 mm

What does Bronze Beetle eat?

These beetles are plant-eaters. Adults and larvae chew the leaves of many plants, such as ribwort plantain, mints and thistles.

Where is Bronze Beetle usually found?

Sunny, open places with plantains and mints, often near the coast

How many legs does Bronze Beetle have?

What do bronze beetles eat?

Leaves. Adults and larvae eat plants from five families, including ribwort plantain, mints and other mint-family plants, rosemary, and thistles such as milk thistle and artichoke. That is an unusually wide menu for a Chrysolina beetle.

Is the bronze beetle a garden pest?

It is not known to be one. California, where it was introduced, lowered its pest rating to C in 2022 because it does not appear to be a significant pest.

Can bronze beetles fly?

Nobody seems to know for sure. It has folded hind wings under its wing cases, and California officials say it “presumably can fly”, but some of its Chrysolina relatives cannot fly at all.

Where do bronze beetles live?

In western Europe from southern England to France, Italy and Iberia, in north-west Africa from Morocco to Tunisia, and on the Canary Islands and Madeira. It has also been introduced to California. In Britain it is mostly found near the coast in the south-west.

When is the best time to see a bronze beetle?

Spring and autumn. Records peak in April and May and again from September to November, with few in July and August. Look on plantains and mint-family plants in sunny, open places.

Why is the bronze beetle so shiny?

Metallic beetle colours come from tiny structures in the shell that reflect light, which is why the colour shifts from bronze to copper or green as you move. Which structure the bronze beetle uses has not been measured.

What is the difference between a bronze beetle and a rosemary beetle?

Both are Chrysolina leaf beetles. The bronze beetle is larger (8–10.7 mm) and plain metallic bronze. The rosemary beetle is 6–7 mm with purple and green stripes and feeds on rosemary, lavender, sage and thyme.

Is it safe to touch a bronze beetle?

We found no reports of bronze beetles harming people. Still, it is best to watch it on its plant rather than pick it up: small beetles are easily hurt, and Chrysolina beetles can give off defensive fluids. If you do touch one, wash your hands.

Snap Map

Zoom in to split clusters and explore where this object has been snapped.

Loading map…

Recent Snaps

Bronze Beetle

Jun 2, 2026

San Juan Bautista State Historic Park

Open source (iNaturalist) ↗

Where to spot

State Park30 sightings12 species

California, US

San Juan Bautista State Historic Park

Adobe Architecture and California History

You might spot Gray Buckeye and California Buckeye.

View guide →

State Park27 sightings6 species

California, US

Coast Dairies State Park

Hiking, Mountain Biking, Coastal Views, Wildlife Viewing, Dog Friendly (partial), Nature Photography, Redwood Forest, Accessible Trails, California Native Plants

You might spot Ochre Sea Star, Giant Green Anemone, and Sunburst Anemone.

View guide →

Take the discovery with you