It's still a mystery why the green and yellow Plague Soldier Beetle, found in temperate southeastern Australia, occasionally builds up to massive numbers.

An unfamiliar yellow and green beetle with a soft body may be a source of curiosity if it turns up in your garden. Will it eat the plants, or bite people? A dozen of the beetles together might start to cause concern. But ten thousand of them festooning a tree are bound to raise alarm. Yet the insect in question won’t harm either you or your plants.

Image of a Plague Soldier Beetle

A Plague Soldier Beetle, Chauliognathus lugubris

It is still something of a mystery why the Plague soldier beetle (Chauliognathus lugubris), a native species found in temperate southeastern Australia, occasionally builds up to massive numbers. Its grubs live in the soil, feeding on other small creatures. The adult beetles don’t seem to eat the plants they settle on, although the sheer weight of a mass of them may break weaker twigs. What they are more interested in is sucking nectar from flowering trees, and copulating.

The bright colours of Chauliognathus are a warning to any predator thinking of taking a swipe at one, as they exude a white viscous fluid from their glands that repels any predators thinking of getting too close.

Close up image of the secreted fluid of a soldier beetle

A close up view of the secreted fluid (Image Victoria Haritos)

The soldier beetle also secretes the same chemical in a wax form to protect it’s eggs against infection.

Our researchers have recently found the genes that give the chemical its anti-microbial and anti-cancer properties, and were able to replicate the synthesis in the lab. This may one day lead to the development of new anti-biotic and anti-cancer related products.

Record a sighting on the Atlas of Living Australia

*UPDATE- Thanks to ‘br’ for leaving this video in our comments thread. We thought it was worth sharing. Prepare to be creeped out by these crawlies…




  1. I too live in Port Melbourne and have hundreds of them on the windows and balconies of my third floor apartment (no plants on my balconies either, but flowering trees nearby). Today when it is 38 degrees outside I came home to find dozens of them had found a way in through gaps in the windows to come inside. Mortein killed them pretty quickly but I’m not looking forward to a summer of this…

    1. All of the palm trees along beaconsfield parade port melbourne are full of them.

  2. We too, here in Beaumaris, have an enormous number of these insects hatching from a couple of places, in particular from the soil of a large pot plant – thousands probably. The plant is healthy and showing no sign of the disturbance all the eggs must have had to the roots. At the moment they are all over the front windows and pergola and having a very sexy time of it.
    Don’t like to spray them if they are harmless, however this is second year and more this time.
    Athough hatching from a different spot.
    Am worried they can get between timber boards of house and next year appear in any gaps inside by mistake as well as out. Is this a concern?
    We have a very tree-y and bushy garden and love the cycle of nature, but with a battle of wills between us and possums, flying foxes and even tree rats, we are feeling sorely tested!

    1. Hi Julie,
      Wild life can be a pain for gardeners can’t it! I battle constantly with possums, rabbits, rats, wombats, and lyre birds!
      I am curious how you know they are hatching from your pot plant – do you actually see them emerging up out of the soil? Do they look any different to the mature adults? Where did they hatch from last year?
      And have you or anyone else seen them in their egg laying phase? I wonder if they all go to the one spot to lay (like your plant pot!) or if they they are laying all over the garden, and what do they lay in -? soft soil of garden beds and pots, in lawns or where? Do they burrow under the surface to lay and then die or do they come up again after laying?
      I’m intrigued by the thousands that are crawling over my paved areas, gravel and lawns. They don’t seem to fly away like the ones on bushes do and don’t look very lively – so I wonder if these have done their egg laying and are now dying? How long after mating do they lay their eggs? Is there an entomologist out there who knows more about them?? They’re a total pain but fascinating!
      Also – someone further down the page said they bite. I’m doubtful of this as I frequently end up with them inside my clothes and I’ve never been bitten.

  3. Hi Jennifer,

    thanks for the tip. I will try that method, they are doing my head in as they are EVERY where, all over my walls out side and leaving yellow spots on my recently cleaned windows. Earlier today they took flight and there were literally thousands in the air.

    Good luck with your 5 acre garden, that must make them a headache for you.


  4. I’m having the same problem as every one above. I originally noticed them a week ago in large numbers hanging off my plants and they have increased 10 fold since then. I certainly hope they are not still around around in 6 weeks as I have overseas guests arriving for Christmas and dining out side with a swarm of beetles is hardly appealing.

    1. Hi Fiona,
      I think I am having some success in reducing numbers by spraying with “Astound” at 1ml per litre (or very slightly stronger e.g.1.2 ml per litre), using an 8L spray bottle. I see in the original article that they secrete a nasty tasting chemical which prevents birds eating them so I hope this is true. I have a 5 acre garden so mine is being a major undertaking, but a normal size garden should be quite easy. I watch for which bushes etc have the most beetles and when (i.e. time of day) and then spray them with a fine mist. I am finding they often disappear at evening so best to do earlier in the day. I try to spray when the sun is not hot on the plant for fear of “burning” the leaves but I suspect I’m being a bit paranoid! Now the pavings, steps and gravel are covered in dead beetles – but easily swept up or blown away.
      We made hay a couple of days ago and the tractor was covered in them so I’m hoping they don’t make the hay taste too horrible for the cows!
      Good luck.

      1. Jennifer;The golden rule when using pestercides / herbercides is first identerify the species if they pose no thret but cosmetic dont apply for the risk of injuring or killing other benifical species is great. Large population of anything need food I suspect that they are eating micro organism like the native bee that comes up in huge numbers when there are outbreaks of aphids; sorry but this atitude of kill the unknow is a bit dark ages. One of the great steps in food production boilogcal controll is the use of bunifical species wether that be plant or animal. Pete Ward Merriwa NSW Ps Where is the spellcheck I have notices many typo errors in my typing. PETE

  5. PS – I meant to add that my beetles arrived in a huge swarm on Nov 11th (11 days ago) and have increased in number since that time; and that I had them last year too when they actually hung around for at least 6 weeks.

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