Tag Archives: Weevil

A Little Weevil House

Key Words: masting, Curculio, Quercus, mast seeding, acorn weevil, diapause

I picked up these acorns (Quercus sp.) when I visited my folks recently in Texas. They have several oak trees on their property and there was an abundance of acorns all over the ground this year, so I brought a few home with me in a ziplock bag. I like acorns. My mom used to draw little faces on them and I had acorn “people” to play with when I was a child.

Acorn “person”

I also found a very cool bug under one of those oak trees while I was there. This strange looking creature is one of the Nut and Acorn Weevils (Curculio sp). It has an extremely long snout. When you find out how this weevil uses it to DRILL, you may be amazed. The adult female weevil will use this drill on her very long snout to make a hole in those acorns!

Nut and Acorn Weevil (Curculio sp).
Nut and Acorn Weevil (Curculio sp).
Nut and Acorn Weevil (Curculio sp).

Keep reading. It really is amazing.

A female weevil will make a hole in the acorn so she can put her eggs inside it!

Hole drilled by Nut and Acorn Weevil

Because I like word games, I thought I’d point out to you that rearranging the letters in the word weevil will make the words “we live?” Well, those eggs hatch into baby weevils who LIVE in a little house that is an acorn (and sometimes in other nuts too). Some folks call them grubs or worms. They are actually the larvae of the adult weevil mom who selected the acorn for her nursery.

If you are assessing this situation from an agricultural perspective (say that nut is a pecan), invested in harvesting a profitable crop, you might be feeling very worried. Sometimes the worry may indeed be justified, but in many cases, like with these acorns, the tree has evolved a strategy to deal with occasional waves of weevils and other insects we consider pests. In actuality, they are just utilizing the resources of the tree like we do when WE (the humans) eat the nut or fruit.

Larvae of Nut and Acorn Weevil (Curculio sp).

I’m going to name the trees’ strategy of dealing with this bug FEAR NO WEEVIL. However, the actual scientific moniker for this strategy (and it applies to other pests and adverse weather stressors as well) is MASTING. The word mast has been used since way back in the Middle Ages to refer to the acorns and seeds of forest trees that drop and accumulate on the ground. It comes from Old English, mæst. Essentially, masting is an ecological term referring to the highly variable and often synchronized periodic cycles of fruiting/seeding in the reproductive processes of trees (both forest and fruit trees).

How is it a strategy for circumventing the deleterious affects of pests? Well, the idea is that in some years, bumper crops of nuts and seeds are produced in order to satiate the predators, so some are left to germinate and continue new generations. In this particular case, you could think of it as the oak trees sacrificing some of their offspring to the weevil gods. When there are more acorns than there are adult female weevils, some of those acorns will escape the weevil drill and makeover into little bug nurseries.

In reality, this relationship is much more complicated. In some cases, acorns parasitized by only a few weevil larvae will germinate, while those acorns with many larvae will not. The trees’ bumper crops of seeds and nuts will also cycle with years of low production, where resources are scarce for the weevil (and other organisms). Nature is incredibly dynamic though. Studies show some species of weevils have adapted a counter mechanism to circumvent the trees’ strategy of masting. It’s called prolonged diapause. This means these weevils are able to sleep longer (more than one year) as they develop in order to synchronize adult emergence with years when the trees’ seed/nut production is high.

If you are interested in reading more about the history and MYSTERY of masting, I encourage you to delve into the literature I’ve listed in the references below. It’s quite fascinating – especially going back in history to the link between masting and pannage. Way more than I can cover here. Check it out.


Baldwin, M. 2021. Pigging out in the forest: the Common of Mast (Pannage) in Britain https://www.wildlifeonline.me.uk/blog/post/pigging-out-in-the-forest-the-common-of-mast-in-britain

Bugguide 2021. Curculio. https://bugguide.net/node/view/6682

Higaki M (2016) Prolonged diapause and seed predation by the acorn weevil, Curculio robustus, in relation to masting of the deciduous oak Quercus acutissima. Entomol Exp Appl 159:338–346. https://doi.org/10.1111/eea.12444

Jefferson, R. 2006. Why Are More Acorns Falling? Excessive Drops of Nuts from Oak Trees Is Part of Normal ‘Mast Year’ Phenomenon. Scientific Times. https://www.sciencetimes.com/articles/33795/20211006/why-more-acorns-falling-excessive-drops-nuts-oak-trees-part.htm and https://youtu.be/EQ748TZcuqs

Jesse, L. No date. The dark side of collecting acorns. Plant and Insect Diagnostic Clinic. Iowa State University Extension and Outreach. https://www.extension.iastate.edu/news/2007/sep/072107.htm

Koenig WD. 2021 A brief history of masting research. Phil. Trans. R. Soc. B 376: 20200423. https://doi.org/10.1098/rstb.2020.0423 Koenig, W. D., & Knops, J. M. H. (2005). The Mystery of Masting in Trees: Some trees reproduce synchronously over large areas, with widespread ecological effects, but how and why? American Scientist93(4), 340–347. http://www.jstor.org/stable/27858609

Nut Leaf Weevil

I found a’nutter weevil! They’ve been everywhere this week! Looks like this may be the Nut Leaf Weevil (Strophosoma melanogrammum). These weevils feed on the leaves of broad leafed shrubs. I saw it on a chunk of rotting alder. It was pretty small and tough to photograph in low light. Probably about 3.2 mm in size. San Juan Island, WA October 13, 2021.

Strophosoma melanogrammum 

Nodding Thistle Rhinoceros Beetle

I found a “new-to-me” bug the other day when I put on my heavy duty gloves and reached to pull out some bull thistle growing in a pile of dirt near our home.  I was being extra careful because the thistle has spines and they kind of hurt when you get them stuck in your hand.   The beetle was right in front of me when I pushed apart some leaves to get a better grasp on the stem.  

Nodding Thistle Receptacle Weevil (Rhinocycyllus conicus) or, The Nodding Rhinoceros Beetle

As I looked a bit more closely, I saw there were quite a few of these beetles on the thistle, especially on the buds.  I went back to the house to get my camera, took some photos, then went about figuring out what this was.  Definitely a beetle. 

It was weevil-like, and pretty hairy.  There were quite a few of them paired up.  They have spring fever like a lot of other bugs I’ve seen of late.  That’s how we get more bugs though, and we need them, whether we like all of them or not.  

(Rhinocyllus conicus) on Bull Thistle

Identification took me about an hour.  I am getting better at piecing bits of information collected over the years.  Bull Thistle is not exactly a popular plant.  It’s managed to get itself on the noxious weed list.  No one seems to want this plant in their garden, aside from Eeyore, who really loves thistle, right?  

Noxious weed made me think of biocontrol.  That narrowed things down a bit and I learned this is the Nodding Thistle Receptacle weevil (Rhinocyllus conicus).  Personally, I’m calling it the Nodding Thistle Rhinoceros Beetle because being in the family Curculionidae, it has the appearance of a nodding rhinoceros. 

 So, the beetle was introduced to control thistle in the US because thistle isn’t welcome, at least the non-native species like bull thistle aren’t.  The part that got me reading to find out more was the adjective used to describe this beetle as “controversial.”  Well, what I found is that the beetle doesn’t just eat non-native thistles.  It eats NATIVE thistles too (Cirsium edule and Cirsium brevistylum).  

Ventral view of my Nodding Thistle Receptacle Beetle – It’s kinda cute!

Why does that matter?  Well, disrupting native ecosystems can have ripple effects.  I found out another reason the beetle is controversial is because there are native pollinators that depend on thistle, like the beautiful Painted Lady Butterflies that we love.  Thistles also produce seed and flax used by our very own state bird, the American Goldfinch. Which brings me to the question, “If the butterflies and birds have begun to utilize the non-native species, are we making the problem worse by introducing another non-native species?”

In my continued reading , I actually began to connect the fact that I buy bags of expensive thistle seed at the store to attract the goldfinches, but I’ve got LIVING food for them in my yard that is free (and also free of pesticides), and here I am pulling it out.   Am I going to waste my energy trying to eradicate a small patch of bull thistle?  Nope.  If it starts to get out of control, we can just mow it down. For now, I am leaving it for the birds and the butterflies…and all the other little creatures I’ve seen living on it.  There were lots of super cute little jumping spiders all over it yesterday!

I’ll leave you with a question. Should we have introduced this hairy little beetle that isn’t native?  I don’t have a good answer.  Maybe it will just help control the spread of thistle and won’t eradicate it entirely.  I’d like to be able to have Painted Lady’s, Goldfinches, and lots of jumping spiders in my garden, even if I occasionally get pricked by the spines of those thistles.  For now, I’m going to stick to improving my drawing skills!