Living With Symbiont Defense

Rash Caused by Pederus Beetles

Rash Caused by Pederus Beetles
Photo: US Army

Rove beetles in the genus, Paederus cause painful dermatitis if crushed against the skin. A rash can last for 2-3 weeks causing the skin to blister. Outbreaks of the beetles in tropical area of Asia can lead to many cases of dermatitis. The US Army has problems with Paederus beetles attracted to lights at security posts in areas where the beetles are common. Their advice, “Don’t stand under the lights and don’t swat the beetles.”

The rash is caused by a toxic agent in the beetle hemolymph called pederin. The pederin is released if the beetle is crushed. A rash eventually goes away when the pederin is shed with the dead skin. The pederin is not produced by the beetle itself, but by a bacterial symbiont that grows within the beetle. The bacteria gets access to food and is transported in the environment by the beetle. The beetle is protected from many potential predators. In the beetle, Paederus fuscipes, only about 90 percent of the females carry the bacteria. Females that do not produce pederin become competent to produce pederin after they have been fed the symbiont. The symbiont is transferred from the female to the eggs. This protects the eggs against predation and ensures transfer of the protective agent to the next generation. How the beetle is able to tolerate the harmful effects of pederin is not clear.

About jjneal

Jonathan Neal is an Associate Professor of Entomology at Purdue University and author of the textbook, Living With Insects (2010). This blog is a forum to communicate about the intersection of insects with people and policy. This is a personal blog. The opinions and materials posted here are those of the author and are in no way connected with those of my employer.
This entry was posted in Biomaterials, by jjneal, Health. Bookmark the permalink.

21 Responses to Living With Symbiont Defense

  1. Anonymous says:

    Gross looking rash! Crazy how the beetles can tolerate the pederin but it’s so irritating to humans.

  2. Anonymous says:

    I wonder if humans could harness this bacteria and use it has a defense/attacking agent in the military force if there ever is any use for it.

  3. Holly Hicks says:

    I wonder how a person would get the beetle off without swatting it. I know that would be most people’s first instinct would be to crush the beetle so i bet that a lot of people from that area would get the rash. It is crazy the way insects evolve to protect themselves from predators.

  4. Virginia Del Real says:

    Very interesting article. I found it interesting that crushing a simple beetle can have such serious side effects. Also, I would like to find out how the beetle is able to sustain pederin on itself and not suffer from any consequences. I’m sure this type of beetle does not have to worry too much about its predators with the pederin it carries!

  5. Antoine Miles says:

    I think it’s really unique that you have to actually smash the but against your skin in oreder for the rash to appear, I would just hope that people try to swat them away instead of on thier skin.

  6. Amanda Frankewich says:

    I found this article very intriguing because several of my older family members have experienced this beetle when they have been deployed. Though none of them were affected, I find it amazing how a parasite can live within an insect for so long without damaging the insect. It is baffling how the beetle has no consequences from carrying this parasite when just smashing the beetle releases pederin which causes a serious skin rash and blistering. I would like to know what chemicals in the beetle’s body protect it from pederin.

  7. Max Deister says:

    This makes me wonder why there is not yet a repellant for the insect. Is finding one too hard or have they just not taken the time to think about it? If one is too hard to find why don’t they provide the security post with suitable bug deferring attire.

  8. Anonymous says:

    To me the most interesting thing about this defense mechanism is that it only activates after the beetle has been killed, as it seems to provide no escape for the crushed beetle.

  9. Sean Cohen says:

    It is very interesting how the beetle can only give a rash to the person by being crushed. It is interesting how the rash itself is not caused by the beetle but by the pederin that is inside. It really is a good defense mechanism, since the rash, and its effects will not go away until the dead skin has been shed.

  10. D Rentz says:

    There is a staphylinid in the Canberra, Australia region that has a tendency to get into the eyes. When it does, it is a big problem. Which chemicals are involved I have no idea but some folks end up in hospital.
    D Rentz

  11. David Yancey says:

    The rash looks pretty disgustingr. Is this a type of way to fight against their enemies? I also wonder if their are any type of ointment that can prevent these type of rashes.

  12. Anonymous says:

    Why do some females not produce the pederin, and who feeds the symbiont them? It says in the post that those that don’t produce the pederin have to be fed the symbiont. Why wouldn’t pederin be passed on to every offspring when it is spread on the eggs.

  13. Anonymous says:

    That is scary. I am scared of bugs period so no matter what it was I would first knock it off of me THEN stomp it to its death.

  14. Asia Smith says:

    That is scary. I am scared of bugs period so no matter what it was I would first knock it off of me THEN stomp it to its death.

  15. Connor Thomas says:

    Very interesting on how the rash is only spread to the human if the beetle itself is crushed. This shows to be a very good example of how animals have come to build their own defense systems. It is also very scary for humans because often swatting bugs is a first initial reaction to bugs. I wonder if their is a some kind of ointment for the rash, or some kind of medicine that dries out your skin extremely and sheds the top layer of the skin to get rid of the rash.

  16. Anonymous says:

    It seems silly to have a defense that only works after the bug is crushed. But if the predator knows what kind of beetle it is and has had a previous encounter with the beetle then it would be worth it. Hopefully you weren’t the first beetle of this kind that a hungry predator ran into.

  17. Drew Maldonado says:

    Interesting! Though I found it pretty pointless that the defense mechanism only works after the bug is crushed. I learned that the rash is actually not caused by the beetle being crushed but perderin reacting. Though I bet this is a great opportunity for research into what pederin could be used for in medical practices.

  18. Anna Monical says:

    I find it very interesting when two organisms can coexist within each other. I wonder why the bacteria does no damage to the beetle though. It seems if it is capable of producing such a rash to humans it might do some damage to the beetle as well. But I suppose they have just progressed enough so as not to have any side effects. I also wonder why not all females have the pederin bacteria, are they somehow different than the 90 percent of females that do have it? Also, are humans at risk of having this bacteria once they have the rash?

  19. Anonymous says:

    I find it very interesting how a bug that small when smashed can cause such a blistering rash on the human skin. but as someone stated early its dumb to have a defense that only works once the beetle is dead

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