Japanese Flower Beetle: All You Need to Know in a Quick Guide

The Japanese flower beetle, more commonly known as the Japanese beetle, is a highly destructive plant pest that can cause substantial damage to gardens, crops, and landscapes. Known scientifically as Popillia japonica, this invasive insect is notorious for feeding on over 300 different ornamental and agricultural plants, making it a major concern for homeowners, gardeners, and farmers alike.

Adult Japanese beetles can be identified by their metallic-green bodies and bronze-colored outer wings, measuring just under half an inch in length. These pests are especially harmful to plants as they skeletonize the foliage, leaving behind a lace-like pattern on the leaves. Their larvae, known as grubs, can also cause significant damage by feeding on grass roots and destroying lawns, golf courses, and pastures.

Japanese Flower Beetle Overview

Appearance

The Japanese flower beetle, also known as the Japanese beetle, is approximately 7/16-inch in length, with a metallic green body and coppery-brown wing covers. They have five patches of whitish hairs on their sides and clubbed antennae that fan out.

Lifecycle

• Eggs: The life cycle of the Japanese beetle begins with eggs laid in the soil by adult females.
• Larvae: These eggs hatch into C-shaped larvae that feed on plant roots, causing damage to lawns, golf courses, and pastures.
• Pupae: The larvae then transform into pupae before emerging as adult beetles, that feed on more than 300 different plants, including foliage, flowers, and fruits.

Invasive Species

The Japanese beetle is native to Japan but was accidentally introduced to the United States in 1916. It is now a widespread and destructive pest in North America, where it is considered an invasive species. Some issues with the Japanese beetle as an invasive species include:

• They damage a wide variety of ornamental, horticultural, and agricultural plants.
• Control methods can be difficult and expensive.
• Their larvae can travel through soil or yard waste, causing the infestation to spread.

Pros and Cons of Japanese Beetles

By being aware of the Japanese flower beetle’s appearance, lifecycle, and invasive nature, we can better understand and manage this problematic pest.

Feeding Habits and Damage

Affected Plants

Japanese flower beetles, also known as Japanese beetles, feed on a variety of plants. Some examples include:

• Ornamental plants
• Flowers
• Grass roots
• Foliage
• Fruit
• Leaves

They are known to cause damage to over 300 types of plants, such as roses, grass, trees, shrubs, and vegetables.

Feeding Patterns

Adult beetles are known for their skeletonizing feeding pattern, where they consume the soft leaf tissue, leaving behind only the veins. Females lay their eggs in turf, and the larvae feed on grass roots, causing damage to lawns and gardens.

Impact on Agriculture

The Japanese flower beetle has a negative impact on agricultural crops, leading to significant economic losses. A few affected crops are:

• Grapes
• Raspberries
• Japanese maple
• Holly
• Dogwood

The damage caused by their feeding can result in reduced crop yield and poor-quality produce. Their feeding patterns not only affect plant health but also make plants more susceptible to diseases and other pests.

To mitigate the damage caused by Japanese flower beetles, gardeners and farmers can use various control methods, such as manually removing beetles by hand, using soapy water traps, or applying chemical control agents. However, each control method has its pros and cons, and effective management requires diligence and persistence.

Prevention and Control

Traps and Pheromones

Japanese beetle traps use pheromones to attract adults, which are most active in June and July. Although traps can be effective in catching beetles, they may also attract more than they catch. Alternative methods include:

• Handpicking beetles off plants
• Placing traps away from desired vegetation
• Emptying traps filled with beetles and water regularly

Natural Predators

Several natural enemies can help control the Japanese beetle population:

• Nematodes attack the grubs in the soil
• Birds feast on adult beetles
• Milky spore bacteria targets the larval stage

Insecticides and Organic Options

For chemical control, insecticides such as neem oil can be used. However, be cautious, as these chemicals may harm beneficial insects like bees. Alternatively, consider organic options:

• Diatomaceous earth
• Milky spore
• Beauveria bassiana fungus

Integrated Pest Management

Integrated Pest Management (IPM) combines various strategies to effectively manage Japanese beetles, such as:

• Regularly monitoring beetle activity
• Using traps and pheromones
• Encouraging natural predators
• Applying insecticides or organic options judiciously

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 – Thick Legged Flower Beetle

?Longhorn Beetle?
Location: Arundel, West Sussex UK
May 20, 2011 5:41 am
Came across this beetle today 20052011 on framework of conservatory.
Could you identify, please?
Signature: Brian

Dear Brian,
Without too much effort, we quickly identified this comely specimen as a male Thick Legged Flower Beetle, Oedemera nobilis, on the National Insect Week website (June 25 – July 1, 2012)  where it states:  “This spectacular metallic-green beetle is usually seen on flowers. Only the male – seen here – has the characteristic thickened hind ‘thighs’ (femora). This species is common in gardens and grassland, and in open spaces in woods, in the south, but is more often found in coastal areas in the north of the country. The larvae feed and develop within plant stems.”  The Natural England website adds this information:  “This species is often seen on the flowers of ox-eye daisies. Another commonly seen species in gardens is a dull sage-green colour. Both are common throughout southern and south east England, but are a lucky rare find in the north, apart from south Cumbria where they are not uncommon.  Adults feed on pollen in a wide variety of open-structured flowers. It may be found on various members of the daisy, carrot and rose family, including hogweed, hawthorn, dogrose and bramble. The larvae live in hollow plant stems.”

Letter 2 – Thick-Legged Flower Beetle

Whats this green bug?
Whats this green bug? Found it last month in Bristol UK someone suggested it’s a “Green horned beetle” or a French friend said a “mante religieuse” but I cannot find it in my book
Thanks
K

Hi K,
We know of a site devoted to common UK Beetles, and this beauty is identified as Oedemera nobilis, the Thick-Legged Flower Beetle in the family Oedemeridae. The site states: “This spectacular metallic-green beetle is usually seen on flowers. Only the male

Letter 3 – Thick Legged Flower Beetle from England

Subject:  Spanish fly?
Geographic location of the bug:  Ipswich east anglia
Date: 05/27/2020
Time: 07:21 AM EDT
Your letter to the bugman:  Hi bugman just spotted this on a margarita plant and can’t identify it! From google images it looks like a spanish fly
How you want your letter signed:  Chris

Dear Chris,
This is not the Blister Beetle commonly called Spanish Fly.  It is a Thick Legged Flower Beetle, Oedemera nobilis, which is profiled on Wildlife Insight where it states it is:  “a common beetle that can be identified by its dazzling colour and gap in the elytra (wing case). This gap in the elytra is not always so obvious but generally gives the appearance of wings that don’t close properly over its back. The males are very distinctive having obvious green bulges in their legs. These beetles certainly catch the eye with their metallic green wing cases glistenening in the sunlight as they feed in the open on flower heads.”

Letter 4 – Spanish Fly and Soft Winged Flower Beetle found on the Isle of Wight

Subject:  Green blister bug?
Geographic location of the bug:  Isle of Wight, UK
Date: 05/25/2019
Time: 02:17 PM EDT
Your letter to the bugman:  Hi, found this bug near Orchard Bay on the Isle of Wight in England. From googling it looks like a green blister bug, but they don’t seem like they’re in the UK?
How you want your letter signed:  Jack

Dear Jack,
This is a very exciting posting for us.  We believe your Blister Beetle is the true Spanish Fly, Lytta vesicatoria, which is pictured on UK Beetle Recording with some southern sightings including the Isle of Wight.  According to NBN Atlas:  “Spanish fly is an emerald-green beetle, Lytta vesicatoria, in the blister beetle family (Meloidae). It and other such species were used in preparations offered by traditional apothecaries, often referred to as Cantharides or Spanish fly. The insect is the source of the terpenoid cantharidin, a toxic blistering agent once used as an aphrodisiac.”  GBIF has an interesting article.  We are very curious about the smaller beetle in your image, which though the coloration is the same, appears to be a different species.

Letter 5 – Thick Legged Flower Beetle

British Flower beetle (very pretty)
Hi again, another picture that i took today whilst out and about. Found this beetle on a Clematis plant which i believe is “Oedemera Nobilis”, this is a Male, as the female lacks the swollen hind legs. Its one of the prettiest beetles i have found in the UK in Hertfordshire.
regards
Ben

Hi Ben,
Please forgive our lengthy delay, but we have had technical difficulties. We received another photo of the Thick Legged Flower Beetle after yours. It is a lovely beetle.

Letter 6 – Thick Legged Flower Beetle

Subject:  Flower beetle?
Geographic location of the bug:  Becontree, Greater London
Date: 06/19/2021
Time: 04:51 AM EDT
Your letter to the bugman:  Hi, I found this little beauty on a flower in my garden. Can you identify it for me please? Many thanks.
How you want your letter signed:  Steve

Dear Steve,
Thanks for sending in your image of a Thick Legged Flower Beetle, Oedemera nobilis. When the lighting is correct, the Thick Legged Flower Beetle appears a beautiful, metallic green color.  According to Bug Life:  “The thick-legged flower beetle is commonly seen on the flowers of ox-eye daisies and other open-structured flowers. They are a common occurrence in gardens in the South of England.”

Letter 7 – Thick Legged Flower Beetle from England

Subject: Shiny green beetle
Location: London SE13
July 6, 2015 6:11 am
Hi
can you help me identify this beetle, reasonable abundant at the moment inmy local cemetary (Brockley & Ladywell), and usually found on flower heads
thanks
Signature: A Smith

Dear A Smith,
We located your beetle on Nature Spot where it is identified as a Swollen Thighed Beetle, Oedemera nobilis, and this information is provided:  “Habitat Flower meadows, gardens and waste ground where they visit flowers.  When to see it April to September.  Life History This beetle is a pollen feeder.”  It is a False Blister Beetle in the family  Oedemeridae.  We found it in our archives and we previously used the common name Thick Legged Flower Beetle.

Letter 8 – Tumbling Flower Beetle

Insect identification
Location: Highlands, near Victoria B.C.
August 4, 2011 11:25 pm
These tiny flying bugs were all over the pearly everlasting flowers. What are they? Can you tell me about their life cycle? Thank you!
Signature: Pattie

Hi Pattie,
This sure looks to us like a Tumbling Flower Beetle in the family Mordellidae, based on photos posted to BugGuide which states they are:  “Common on flowers and foliage; sometimes on dead trees and logs. Larvae occur in dead or dying hardwoods, in pith of weeds or in bracket fungi.”  BugGuide also remarks that they are:  “small, wedge-shaped beetles; body arched, head bent downward; abdomen usually prolonged into a style or pointed process; hind legs in most species very long and stout, fitted for leaping; antennae long and slender; thorax as wide at base as the elytra. The body is densely covered with fine silky hairs, usually black, but often very prettily spotted or banded with yellow or silvery hues. The adults occur on flowers or on dead trees and are very active, flying and running with great rapidity and in the net or beating umbrella jumping and tumbling about in grotesque manner in their efforts to escape. The larvae live in old wood or in the pith of plants, and those of some species are said to be carnivorous in habit, feeding upon the young of Lepidoptera and Diptera which they find in the plant stems.”

Letter 9 – Tumbling Flower Beetle

Subject:  Beneficial or pest
Geographic location of the bug:  Central Florida
Date: 05/13/2018
Time: 11:41 AM EDT
Your letter to the bugman:  Its May and I’ve seen this bug on my black eyed Susan and also on basil, tough I cannot see any leaf damage. It seems just to be resting on leaves and flowers but not actively eating leaf nor bug. What is it?
How you want your letter signed:  Omar

Dear Omar,
This is a Tumbling Flower Beetle in the family Mordellidae and based on this BugGuide image, we are confident the species is Mordella knulli.  Of the family, BugGuide states:  “Larvae are believed to eat plant material in decaying wood, etc. Some are leaf and stem miners. Some are predaceous. Adults visit flowers.”  Based on that, we would say it is beneficial, though benign might be a better term.

Letter 10 – Tumbling Flower Beetles

Subject:  Black bugs in roses
Geographic location of the bug:  Thatcher, Az
Date: 10/12/2017
Time: 08:52 PM EDT
Finding lots of thin little black bugs inside the petals of roses.
How you want your letter signed:  Dawn

Dear Dawn,
Based on this BugGuide image, these look like Tumbling Flower Beetles in the family Mordellidae.  According to BugGuide, they are also called “Pintail Beetles” and “Common on flowers and foliage; sometimes on dead trees and logs. Larvae occur in dead or dying hardwoods, in pith of weeds or in bracket fungi.”