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 am very disappointed to hear of so many people wanting to rid themselves of these bugs. No wonder we have a global issue of declining biodiversity. Our eucalpyt in the front yard is totally covered in the beetles and the lawn too. They get onto the car and underfoot in the driveway but my 6yo and I find them fascinating and beautiful. They have not caused any problems for us. If anything they have eaten my aphids and the roses have never looked better! The eucalypt seems fine. Enjoy the brief show of nature doing what it does best and please don’t kill them!!!

  2. Sorry to be tedious, but another vital point! If you are spraying with insecticides over large areas its important to do so early in the morning before the bees are out foraging. Bees are in enough trouble already without us making things worse.

    1. The bees you are trying to protect are not native bees, but rather the invasive European honeybee. I too thought that the bee crisis was alarming until I was better informed by my professor. These bees compete with native birds and mammals for valuable tree hollows, kill nestlings with stings, facilitate the spread of invasive plants and out-compete our own native bees.

      1. Thanks for your comment Anonymous, but aren’t European honeybees important for pollinating our crops and fruit trees? I thought this was why we are so concerned that verroa mite will get into the country (most consider this inevitable) because it will devastate agriculture? Are you saying we’d be better off without the European honeybee? Does your professor think this? Can native bees do all that they do? Could you perhaps let me know as I am very interested.
        And I am concerned about killing native bees – I have lots in my garden and don’t want to kill them either!

  3. PS – I found several articles indicating that alpha cypermethrin is not harmful to birds themselves but was left in some doubt as to its effect on their fertility.

  4. I have just watched a blue wren eating dying beetles on my patio. Perhaps when the beetles are dying they don’t secrete their repelling substance? does anyone actually know if “Astound” (alpha cypermethrin) is harmful to birds? We all know about DDT making eggs not hatch.
    I apologise for labouring the point but I think its important we know more about chemical control if these beetles are going to become a yearly event. Is there any compound that we can be confident won’t harm birds?
    I am disappointed that the CSIRO isn’t better informed and being more helpful with information on this post.

    1. Hi Jennifer,
      You are not being tedious,it is very important we are fully informed. I haven’t sprayed yet as we are a bit hectic at the moment however I was a bit hesitant because we have a wonderful bird life here and I would hate to do any damage. I agree with you that the CSIRO need to be more helpful with information.

      1. Hi Fiona,
        I think my beetles are disappearing so you probably don’t need to spray after all. There are lots crawling on the ground ? dying but only a few flying around. I can’t believe I’ve reduced the population this much with my spraying so I’m thinking its the end of their natural cycle. Seems they were here en masse for 3 weeks only – not the 6 I was dreading! What a relief to have my garden back – just need for the stink of them rotting to disappear now!

      2. Hi Fiona,
        Seems my beetles are finally disappearing so you probably don’t need to spray after all. There are still lots crawling around on the ground? dying but only a few in the bushes and flying around. I can’t believe my spraying has reduced the population this much so I think it must be the end of their natural cycle. They were only here en masse for 3 weeks not the 6 I was dreading! How nice to have my garden back – all I need now is for the smell of them rotting on the ground to go too!

    2. Hi Jennifer,

      yes mine are starting to disappear as well, only a few days ago I started to notice dead ones on the ground and I’m not sure if it’s the cold wet weather but they have all but disappeared.I would also say it was a 3 weeks from the time I first noticed them until finding the dead ones.They certainly peaked when the weather was hot and I noticed a pattern of flight and rest. Mid day was a peak flight period with literally thousands in the sky and then resting early morning and late afternoon. I hope this is helpful to anyone else reading.

      Thanks, Jennifer

      1. Mine are still around after 4 weeks, I have tried spraying which has reduced numbers but not to the extent I was hoping. They have also left horrible yellow streaks on the exterior paint on my house wich seems to have stained.

    3. Hello Jennifer, and others,
      I believe it both logical and ludicrous to spray anything that other wildlife may eat. Of course that chemical will be digested by the predator. I don’t pretend to know what effects this may have, but logic surely helps your decision in doing so. If you want to control this insect, there are 2 approaches, larvae control and adult control. If you are sure they are laying eggs in your property, then late winter, early spring ground control much like the scarb/lawn beetle. Get them before they come up, and reduces the population therein. Adult control should be contact (not systemic sprays) and the deceased removed immediately to avoid follow on effect. They are harmless, live with it, they love pollen, hence high activity lately. They start leaving/dieing as soon as they have mated and layed eggs.
      Hope this helps, from a professional gardener of the bayside area for more than 23 years

  5. We live in Chelsea and have the same problem as mentioned by others. I don’t agree with “They are harmless”. These huge swarms this year are destroying our native trees and other plants (they live under the bark at night, and our trees have no bark left where they reside. Apart from that, they bite or sting. We and our pets cannot go outside. And the CSIRO are saying ‘they’re harmless??? Last year, the first time we noticed them they completely destroyed one of our Gum trees. It was literally eaten alive and subsequently had to have it removed.

    1. Hi Elke, sorry to dissapoint you on what you think harmed some trees or even killed your gum tree. Firstly, what varieties of trees are they residing in? Are they trees that shed bark?. If so,then the bark would shed anyway and not much harm done. How are you prosposing that these beetles get under the bark? Are there holes/splits etc in the trees? It is an undisputable FACT that these beetles eat nectar/pollen, and the odd aphid/small invertebrate, so ripping bark off a healthy tree is nigh impossible. So, it is highly unlikely the soldiers residing on trees are destroying them from inside out. In relation to your gum tree, unless they were in massive proportions breaking ALL the small limbs, hence weakening its strength, then this is also highly unlikely. Perhaps some further research into your trees health might be beneficial for you. Are you getting severe dieback often? Perhaps something like borer is attacking?
      I have these liitle fellas crawling all over me when working and have never been bitten.
      I am a professional gardener that has worked in the bayside area for 23 years. Hope this may help.

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