Are the European beetles in the PNW actually doing any harm? If so, should we, or should we not interfere

This post is specifically about whether or not invasive European beetles here in the PNW are actually doing harm or not, to people, or to the native organisms. And if they are doing any notable harm, which species are we talking about?, should we be trying to ‘rid ourselves of them?’ Or, should we just let nature eventually run its course with them, and decide whether or not the ‘invaders’ will be here for a long time, or for very little time.

In this post, we are going to include all of the invasive/adventive European Coleopterans that we want to, as long as they are species that were accidentally introduced here in the Pacific Northwest. Oregon, Washington, and British Columbia in this case.

Normally, when I am asked to name the first species that comes to mind when asked for an invasive species here in the PNW, my brain usually goes to Nebria brevicollis, or Pterostichus melanarius, but that is mainly because I have become so used to working with and around them that they are an automatic response sometimes. But I still know there are many other invasive/adventive beetles here, and there are, of course, also many other European beetles that weren’t intentionally introduced to the PNW.

I hope that some or all of the posts/comments/replies in this will be helpful to anyone who is interested in this topic.

I give my best regards,

Connor Graham

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You may have already read this paper–as it poses the same question:

Yes, I have read it many times just because I felt like it, and when I am studying N.brevicollis and feel like I missed something that I had read before, and I know that the article poses the same question, in a way. As far as I can tell, the article is only posing the question as an unknown, and does not have an official answer, and it also appears to be only directing this proposed question towards N.brevicollis, and not the other invasive European beetles that are in the PNW.

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I don’t have an answer for this specific question, but in general it can actually be really difficult to tell if something will become an invasive species or not. It may enter the ecosystem and hang around for a while, slowly spreading without much impact, then suddenly take off in numbers and become a serious problem many years or decades later once some tipping point is reached.


If an invasive species was introduced by humans, whether accidentally or not, some effort should be made to remove it. Particularly since we’ve already messed things up pretty badly, without any given native environment also having to deal with invasive species. If they aren’t doing any harm, better to focus time, energy, and money on things that are actual problems. And if it’s not doing any harm, I don’t think it’s considered to be an invasive species? Invasive species are ones that are harmful to the native species. If something is nonnative but not doing any harm, that’s just an introduced species, like most (if not all?) woodlice in the US.

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The impacts of a small invertebrate, even if dramatic, are much less likely to be noticed than those of a larger animal or plant. The beetles might have a severe effect on some other, native beetle, without anyone ever noticing. We just don’t have detailed abundance and distribution data for many invertebrate species.

In this case, it seems that the horse has already bolted, and getting rid of these beetles would be very difficult. I’d suggest that while we should assume there is a good chance of some negative effect, the focus should be on biosecurity to avoid introduction of any further non-native species that might become invasive.


I guess it all comes down to practicalities, really. If the beetle is affecting native beetles, how to control it becomes the key question. Spray insecticide? Pheromone traps? Sterilize males and release them? Eradication of introduces species is difficult in a large area - control can sometimes be achieved but some people believe that eradication cannot. I found this interesting piece with a range of opinions - If an invasive species was successfully eradicated from an ecosystem, would the native species in the area thrive as much as they originally did? (

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