Western Conifer Seed Bug

2007 November 3

Assassin, or innocent bystander?


Last week, we had an assassin bug. So, what’s this one? At first glance, it doesn’t look all that much different from the assassin bug, other than coloration[1]. It even looks like it has a neck. If we look closer, though, there is a key feature that gives it away: the middle section of the hind legs (the tibia) is flattened and enlarged, kind of like a leaf.


This is a feature of “leaf-footed bugs”, (family Coreidae). Looking more closely at the exact shape of the “leaf”, the coloration, the markings on the wings[2],


the eyes,


and the antennae,


I’m pretty sure that it is a Western Conifer Seed Bug, Leptoglossus occidentalis.

These guys are actually a recent arrival in the area. The are native to the West Coast, but according to this article they had expanded their range into Michigan as of the early 1990s.

As an invasive species, this is a bit different than usual. Most invasive species in this area seem to have come from another continent altogether (usually Eurasia)[3]. Leptoglossus occidentalis was in North America all along, and is currently just expanding its range due to changed conditions. And what changed conditions might that be, you ask? Well, it sounds like what happened was that several eastern species of pine trees (Red pine, Eastern White pine, Scots pine) and one European species (Austrian pine) have been introduced in tree plantations in the west. These were all trees that Leptoglossus occidentalis could feed on, and have basically made it possible for them to have a continuous chain of host plants leading all the way across the mountains and great plains to the east.

As for their habits, they overwinter as adults. In the spring, they lay their eggs on immature pinecones, and the nymphs evidently suck juices out of the developing cones and seeds (since they are true bugs, they have the characteristic piercing/sucking mouthparts and so can’t actually chew anything up). They mature by late summer, and then find someplace to overwinter. This often means somebody’s house, which is why we found a couple of them strolling around our bedroom this year in early October.

[1] As I said last week, I had thought the actual assassin bug we found was a harmless squash bug and handled it very carelessly, only avoiding getting bitten by pure luck. This time, I thought this bug was an assassin bug and handled it with care, and then it turns out it was completely harmless. It figures. Although, maybe not completely harmless; in regards to another bug that only sucks plant juices, Serendith sent me this comment a while back regarding cicadas:

“The long stylet is used to puncture branches (the same way other true bugs do). I have kept them at the museum and they only live if I give them trees that the species likes to feed off of. Beyond that – one “bit” my boss (pierced him is more like it) in what we believe was an investigatory sip … creeped him out and hurt a little but no lasting damage.”

I expect that any bug that can drill a hole in wood to suck sap out, won’t have any trouble with human flesh if they are so inclined. It’s just that they normally aren’t so inclined. Of course, since plant-sap-sucking bugs won’t inject digestive fluids and toxins the way that predatory bugs will, it shouldn’t be as painful as an assassin bug bite.

[2] These wings are a good example of the feature that the true bugs (Hemiptera) are named after. Hemiptera is greek for “Half wing”, and the forewings of true bugs are often hard and opaque in the front portion, and membranous at the ends (the hindwings are tucked under the forewings).

[3] Although, particuarly up here in the Upper Peninsula, the key difference between an “Invasive Species” and a “Native Species” is that the “native” species got here before anybody was keeping records, and the “invasive” species got here afterwards. Given that this was one of the last places in the US that the glaciers pulled out of, nothing has been here longer than 10,000 years, and only a few things have been here as long as 8,000. Some of the trees, like Eastern Hemlock, have only been here about 2000 years. In general, it sounds like this area never did reach a steady-state ecosystem between the melting of the ice and the arrival of the lumberjacks in the 1800s, and certainly didn’t have enough time to evolve much in the way of unique species.

14 Responses
  1. Cindy permalink
    October 17, 2008

    I took a picture of this kind of bug and have been hunting for its identity. Thanks for the info!

  2. October 18, 2008

    Glad to be helpful.

  3. Sarah permalink
    April 18, 2009

    I just caught one of these and have been trying to identify it. Some of my siblings and I had thought it was an assassin bug but I guess not! Thanks for helping me identify it!

  4. Becky permalink
    September 24, 2009

    I think this is what is outside my house! Thank you for helping me figure it out… Although I sure hope they don’t overwinter IN my house.

  5. Bill permalink
    October 22, 2009

    Thanks Tim. I’ve been wondering what this was for seven years.

  6. December 10, 2011

    So, I’m kind of confused, but what exactly can these bugs eat during adulthood?

  7. December 11, 2011

    As far as I can tell, they eat sap from conifer trees during their whole lives. True bugs like these don’t change much as they grow up, and usually the adults eat the same things that they ate as nymphs. It is the insects that have a complete metamorphosis from a caterpillar/grub (like butterflies and moths) that most often change their diets radically after they become adults.

  8. December 15, 2011

    Thank you for this information. I’m kind of on this small mission to learn more about these bugs. They’ve always seemed somewhat remarkable. Now what you’ve told me so far about their dieting habits was valuable and all, but believe it or not, I’m a little more confused than I was before. You see, I too have an Assassin bug crawling arond my house at this time of year, and it spent so much time in my room, that I kina grew close to it. No matter how scary it looked at first, it never really did me any harm. It kept great distance, sort of came and went, and it moved in such an interesting and peaceful way. So when my niece got scared of it and wanted me to kill it, I just couldn’t find the heart to treat it that way. So I’ve kept it, reasoning that I’d keep it for observance for these twins I look after. Now my niece herself wants to take it for show and tell.

    Now I’ve been looking up different sites on the assassain bug, and really it’s like reading scattered pieces of information that someone copied from other sources themselves. I’m either getting information about all these other groups of assassin bugs, or else it’s indirect info. about the one I have ( which, by the way, is the same one in the picture). I’m espescially annoyed about its dieting info. One site about these bugs in captivity stated that they’re supposed to eat caterpillars and earthworms, but I don’t know where to find that. They never seemed to mention anything about pine either. It’s frustrating because my niece has to bring this thing to school soon, and I still don’t feel like I know enough facts to give her. Just as much, I really don’t want to weaken this thing if it doesn’t have what it needs. It already seems to be moving slower, desiring more space, and getting annoyed by various movement with a stick just to be put in the same place. I’m lucky I haven’t gotten bit yet. With all this hassle, I really prefer to let this thing go now. It’ s crawling aound in a circle of boredom as I speak. Even the kids are losing interest, especially since we all found out about its sinister biting.

    So excuse my long letter, but now that you can see my anguish here, do you have any other accurate information on “this” particular “acholli multispinosa”? <—– (quote of a site) Aaannd are you sure this thing lives off of pine?

  9. December 15, 2011


    The bug I have pictures of on this page is a Western Conifer Seed Bug. It is not an assassin bug, although some assassin bugs look kind of similar to it. It only eats plant juices, and is not closely related to the assassin bugs. Check the hind legs of yours. If they have flattened bulges on them like you see in my second picture above, then this is what you have.

    If you have a Western Conifer Seed Bug, then at this time of year it isn’t looking for anything to eat. It just wants a place to hibernate. The best thing would probably be to give it a piece of water-soaked paper towel so that it can have some moisture, because it is probably drying out. Then put it into your refrigerator so that it will go dormant until Show & Tell time, and let it go afterwards. It may die anyway (insects often die for no obvious reason), but this is probably your best bet for keeping it alive and healthy for a while at least.

    If your bug does *not* have the flattened bulges on its hind legs, then it probably *is* an assassin bug such as Acholli multispinosa. In which case, it will eat any other kind of insect that it can get. Other insects that you might have getting into the house (particularly flies) should do fine to feed it in that case. Just remember that even if you do everything right, it will probably die of old age within a few weeks or months.

  10. December 15, 2011

    Thank you so much for this new info. It truly feels like a breath of fresh air to find all this out. Really, my niece’s class does show and tell tomorrow. She’s waiting for the information I promised her tonight, and now I feel like I could give her a full report just from what you’ve told me! It almost feels like my own assignment to turn in, lol. oh, and I’m so glad I don’t have to dig up any worms or buy feeder food at a pet store meant for a more necessary animal. Kudos to you, Tim. You’re a bug savior. I’m gonna try the moisture thing too. As random as it is for bugs to die, I really hope Beetle Boy ( I thought it fit him–(or her) :} ) holds out until tomorrow.

  11. December 15, 2011

    ooh ooh and, yes, i looked and he is one! Now my only wonder is if Beetle Boy is really Beetle Girl.

  12. Dawn permalink
    January 10, 2012

    I have these types of bugs crawling around my house and they look similar to the one pictured however when we get rid of them they leave an awful smell. Now I thought they were called stink bugs because of that but am I wrong?

  13. January 10, 2012

    There are a lot of different kind of “stink bugs”, the name pretty much applies to any true bug (suborder Heteroptera) that gives off a bad smell to defend itself. Since these are true bugs, and they certainly do give off a bad smell, you are perfectly correct to call then stink bugs.
    Most of the other stink bug species are shorter and broader across the shoulders than these are.

  14. Gary permalink
    October 5, 2012

    They’re EVERYWHERE this year at my house (southcentral UP) and YES they do stink. It’s not so much like a pungent smell, but almost like a sweet smell, oversweet or something, real bad! Thanks for the id on these buggers.

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