Japanese beetle
Popillia japonica
Metallic green-and-copper beetles that skeletonize leaves and flowers in mid-summer. Knock into soapy water in the cool of morning; avoid pheromone traps near the garden.
How to know it
A handsome beetle 10–12 mm long with a metallic green thorax, copper wing cases and five tufts of white hair along each side. They feed in groups on the sunniest, highest foliage; the grubs are fat white C-shaped larvae in the lawn beneath.
What you'll see
- Leaves skeletonized to a lace of veins, worst at the top of the plant and in full sun.
- Groups of beetles feeding and mating openly on roses, grapes and beans.
- Flowers chewed to tatters, especially pale roses and hibiscus.
- Brown irregular patches in the lawn that lift like a carpet, with white grubs beneath.
- Crows, badgers or skunks tearing up turf to get at those grubs.
Where it comes from
Adults fly for six to eight weeks in midsummer, feeding by day and laying eggs in short, moist turf. The grubs feed on grass roots through autumn, move deeper to overwinter, and finish feeding in spring before pupating — so lawn damage and leaf damage are the same insect at different times of year.
Established across much of North America and now spreading in southern Europe; a notifiable quarantine pest in the UK. Warm summers and irrigated lawns favor it — the lawn is the nursery.
Dealing with it
- Knock beetles into a jar of soapy water first thing in the morning, when they are cold and clumsy.
- Do not hang pheromone traps in the garden — they pull in far more beetles than they catch.
- Cover prize plants with fine netting during the few weeks of adult flight.
- Treat the lawn with parasitic nematodes (Heterorhabditis) in late summer while the grubs are small and near the surface.
- Let the lawn go dry in midsummer; beetles avoid laying in hard, dry turf.
Keeping it out
- Keep lawns lean and un-irrigated through the flight period, or accept that they are the nursery.
- Report sightings in the UK, where it is notifiable and not yet established.
- Grow less-favored plants — lilac, boxwood, holly, forsythia — near the worst-hit spots.
- Apply nematodes annually in areas with a known population.
- Encourage starlings, tachinid flies and parasitic wasps rather than reaching for sprays.
What it goes for
Over 300 plants: roses, grapes, raspberries, beans, sweetcorn, apples, cherries, birch, lime and hibiscus especially.
Who hunts it for you
- Assassin bugReduviidae A patient ambusher with a curved beak it drives into whatever it catches — caterpillars, beetles, bugs, and the occasional bee, so count it a generalist rather than a specialist. It will jab a careless finger too, so admire it and leave it be. Grow to recruit it: Dill,Fennel,Goldenrod,Sweet alyssum,Tansy,Yarrow
- Beneficial nematodesSteinernema & Heterorhabditis spp. Microscopic worms watered onto damp soil that hunt down soil-dwelling grubs and release a bacterium that kills them within days. Timing is the whole thing: warm, damp soil and a small target grub, which means late summer for most of what they are used against.
- Garden birdsPasseriformes Both things are true: birds strip your currants and a brood of blue tits takes several thousand caterpillars out of one fruit tree in a fortnight. Net what you must and welcome them everywhere else — a nest box near the apples is worth more than a spray. Grow to recruit it: Echinacea,Elderberry,English holly,Goldenrod,Rudbeckia,Sunflower
- Praying mantisMantidae A sit-and-wait ambusher that snatches caterpillars, beetles, and anything else that wanders close — friend and foe alike, so count it a mixed blessing. Tall, structured plantings give it perches and egg-case anchors. Grow to recruit it: Cosmos,Fennel,Sunflower
- Spined soldier bugPodisus maculiventris A predatory stink bug — same shield outline as the pest, but with a sharp spine at each shoulder and a beak it uses to spear caterpillars and beetle grubs. Learn the spines before you squash a shield bug, because this one is on your side. Grow to recruit it: Dill,Fennel,Sweet alyssum,Yarrow
- Tachinid flyTachinidae Bristly, house-fly-lookalike parasitoids that lay eggs on caterpillars, beetle grubs, and earwigs — the maggot consumes the host from within. Adults sip nectar from shallow umbels and daisies. Grow to recruit it: Cilantro,Dill,Feverfew,Parsley,Sweet alyssum
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com