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. Good afternoon. I have a question. Do these beetles get into the water. Last year at Seaford beach there was a swarm of beetles matching the description of these. My daugther was bitten while in the water. She came out in a huge rash and this rash continues to occur when she gets hot or wet. Any information as life for her can be uncomfortable.

  2. Our neighborhood is swarming with Soldier Beetles have never seen anything like it before in Eltham. We live among lots of gum trees and many are currently flowering.

  3. Hi guys… my back door and verandah is currently covered in them. I figure they will head off when it cools down but to get them moving I have placed some mozzie coils down… they are not impressed and have started relocating back to the garden and surrounding trees.
    Hope this helps.

  4. Hi there – we currently have thousands of these beetles in the tree at our local primary school (Ringwood North) and secondary groups of them around rocks in the garden. It’s good to know they’re harmless!

  5. Hey rachael, they wont hurt your plants, from what i read, they are great at controlling other insects like aphids and caterpillars. Does anyone know if chickens would eat these beetles? or are they toxic as the colour of their body might suggest?

    1. Hi linton and others,

      My observation and reading lead me to believe that chickens are unlikely to eat them (unless they are really hungry!) and that if they do they won’t do them any harm. I don’t think the actual beetle is toxic – just doesn’t taste very nice.

      And Rachael – I also had them all over my vegie garden and don’t think they did much harm to anything. I did spray them just once however with alpha cypemethrin (tradename “Astound” -withholding period for fruit and veg only 24 hours) as I was trying to reduce numbers generally. After they’d fallen off everything looked ok.
      If anyone does feel they need to spray, alpha cypermethrin (10ml/8L) is considered safe for birds (and chooks!) that might eat them. There may well be other sprays that CSIRO might care to recommend that could be better. (Some qualified input from those who initiated this post would be much appreciated!) I only used “Astound” because I happened to have some. “Confidor” (Imidacloprid), which the staff at Bunnings(!) tell me is the safest insecticide on the market (apart from pyrethrum) would very likely work also.

      MIne were here in HUGE numbers for about 3 and 1/2 weeks and a few stragglers for another week or so. For those of you still inundated I hope they go soon. The general experience seems to suggest they probably will. But please let us know.

      1. I became very ill after spraying Confidor on palms indoors, not taking precaution with mask or ventilation because it was said to be “safe”. This and all such sprays are toxic and you would be wise to acknowledge that.

        If you are spraying a chemical to kill anything then you must take responsibility for the collateral damage. Which is more valuable to you: the health of the bird & bee population or lack of yellow marks on windows or walls? Will you then also spray to kill the aphids next spring that the larvae of these beetles would have eaten had you not spread toxins to kill them?

        I am disgusted to see what is written here, on a scientific website, when even commercial pest eradication websites advise to not spray toxins on soldier beetles. Please re-evaluate your priorities.

      2. Hi, I am very concerned about all of this talk about spraying pesticides – PLEASE READ THE MSDS SHEET WHICH IS PROVIDED WITH ALL PRODUCTS before spraying! DDT is a well known bad pesticides, but Malathion is also an Organophosphate which is very bad. I have read it is regarded low toxicity for humans, but many of these build up in the environment. Remember we used to spray DDT on kids as an insect repellant. Please don’t use chemicals unless there is no choice!

        also, Imidacloprids are neonicitinoids which are thought to be killing off our bees – safe for us, but not safe for anything else.

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