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. old thread but very informative. I just assembled a large playground set from Costco which had bright YELLOW slides. These beetles appeared from everywhere, swarming on the slides nd now everywhere in the garden near the set.

  2. I have squillions of them falling from my big gum tree which is flowering. It is a relief that they don’t do much damage to gardens and that the larvae eat other insects. That makes them good guys.

  3. This website was… how do you say it? Relevant!! Finally I’ve found something which helped me.

    Thank you!

    1. Your website was informative and satisfied all my queries. Although I still think I got nipped on the foot by a soldier beetle as they were the only possibility. I would like to stay on your email list.

  4. A PS (thanks Jesse): It’s under a week and we’re down to the last few billion. They definitely have to go as one hitched a ride with me to Coles yesterday! Gave me a little bite – not a sting exactly, but maybe a squirt of their stuff, which left an irritation. They definitely do (as Craig noted above) leave small holes in foliage/leaves, which then shrivel. I guess they have to eat something. But this is not good for babies under cultivation as there needs to be enough leaf on the plant for it to photosynthesise and grow. My test plants? I have a small collection of unusual hellebores under cultivation and all the leaves are affected; ditto Xmas Liliums in pots just out (always flower late here) now dotted with small holes in petals, a disappointment. They are definitely selective, but in such numbers it’s hard to observe a pollen pattern. A small local native ground cover (bearing small flowers) that was swarmed from the first day is pretty much lace now, yet another native ground cover adjacent to it (no flowers) has been spared.

    I guess compared to the farmers it could be a jolly sight worse. A plague of locusts maybe! But I thought it worth corroborating Craig’s observations (and others) with my own.

    It occurs to me that the benefit/harm ratio is a function of numbers. We don’t have so many bad bugs to need the benefit so much. It’s Malthusian (?). There’s not enough food supply or surface area (and no predators), so they hit the plants (is it what they secrete that damages the plants?). As to predators, it is possible that the wattlebird up here may be slightly keen but the jury is still out.

    Strategy past two days has been to hit the remainder with granny’s all-purpose soap pesticide, which seems to be effective. It’s not dramatically effective but the numbers of corpses are building up and the living are retreating to smaller clumps where they think I can’t see them (oh but I can!). Seems they try to get a wriggle on but then crash and expire.

    Recipe: boil up old soap chips (I add crashed garlic cloves for good measure) and store the jelly in jars; dollop into recycled spray bottles as needed, add water and shake (will dissolve standing over time anyway). Works brilliantly, especially on roses – at least till the ladybug population builds up!). The solution needs to be viscous enough to seize their engines and thin enough to get through the nozzle. Big bonus is I can sweep the last few squillian corpses into the compost having no more worries about residual toxins.

    For me the go next time will be:

    Stage 1: Broad sweep direct Pyrethrum application (showing no mercy!); bin corpses.
    Stage 2: Broad sweep direct soap application (still showing no mercy), compost remaining protein.

    Hope this is of some help to all you plague soldier beetle victims out there!

  5. Wish I’d read the previous post about the soap solution. Have just had a local infestation in my garden in Katoomba, NSW (possibly due to a giant overhanging late flowering wattle from next door, but who knows). As we are in the process of landscaping a native garden/wildlife corridor under all sorts of weather and time constraints I was not relishing further delays with the discomfort of millions of pesky insects flying about and smothering everything in sight over an indefinite period. Our garden is pretty ecobalanced and chemical free so we are not in need of these helpful native critters in such apocalyptic numbers! 🙂

    As an editor I was also worried about the prospect of having my workplace under siege…on the third day they were starting to crawl into the house!. Only plus was the disappearance of the European wasps!

    I usually make up my own bulk insecticide from a diluted solution of soap chips and garlic, but as I was in a bit of a panic (had never encounted this before) I went into a mild panic so didn’t think of using the preparations I had. I rang two pest control companies who were both completely unhelpful. So I figured that with no bird predators, pyrethrum was the go.

    I used a single application of pyrethrum which I applied directly to clumps simply to reduce the sheer weight of numbers placing a strain on immature natives under cultivation. This seems to have had immediate effect and I’m not overly worried about the impact on the birdlife here. We have to get the natives up so we can have the birdlife!

    Wonderful to find this informative site, which helped me not to panic and to get things sorted.

    Hoping the rest will get the message and bugger off. If not, it’s the soapy solution for them.


    1. Thanks for the great advice! You’ve saved many readers’ gardens, to be sure.

      CSIRO Social Media Staff

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