Nearly-decapitated sunflower heads, scattered across the prairie. Oh, the devastation! Who could be carrying out such an evil plan?
(Ok, more accurately, a weevil plan?)
I found this sad-looking stiff sunflower (Helianthus pauciflorus) during a prairie hike back in August.
Stiff sunflower was not the only species being targeted. Maximilian sunflowers (Helianthus maximiliani) were also dangling… This photo was taken just a few minutes after the first.
The head-clipping weevil, aka the Silphium weevil (Haplorhynchites aeneus) is a small dark-colored weevil, less than a centimeter in length. Females girdle the stems beneath sunflower heads – as well as other plants such as compass plant and rosinweed – so that the flower head falls over, but usually doesn’t drop completely off, at least not right away. Once a flower has been knocked over, other weevils usually show up – male and female – to feed on pollen, mate, and lay eggs in the blossom.
Doing some research for this post, it was hard for me to confirm what happens next, but it seems the eggs usually don’t hatch until the flower eventually falls to the ground. The larvae feed on the decomposing flower head and then burrow into the earth to overwinter. It is thought that clipping the flower before laying eggs on it might make the flower a less attractive place for other insects to lay eggs, saving more food for the weevil larvae.
Before that August hike, I hadrarely seen the head-clipping weevil itself, and had never photographed it. Not long after looking at the sunflowers shown above, I finally saw a weevil fly off and managed to get a documentary photo of it when it landed. Look at all the sunflower pollen stuck to it!
The clipping behavior by weevils can cause problems for those raising sunflowers commercially, but I’ve never seen it impact enough flowers to cause any serious issues in prairies. I’m guessing that some of you readers will know much more about the head-clipping weevil than I do, and I hope you’ll contribute additional information in the comments section below. Thanks in advance!
So, to summarize the weevil plan: The weevil female nearly decapitates a flower and then mates with weevil males and lays weevil eggs right on the mortally wounded blossom. The weevil babies eat the dying flower and then burrow into the ground until the next spring. Then they make a triumphant return and hatch their weevil plans once again. And who do we have to thank for finding out about all of this?
Weevil scientists, of course!
The Prairie Ecologist 
Go for it, Chris! For good or weevil, this was a most interesting blog!
Thanks, Chris. I send my prairie restoration group a monthly update, and I’ll be sure to include a link to this blog post in my December one. It’s been a hot question this season — we had a lot of decapitations! I always appreciate your informative, well-written posts. Keep ’em coming!
Your sense of humor brightened my morning considerably!
These weevils are alive and well in NE Indiana. Now I know what has been happening to my Silphiums… thanks!
Every year in my prairie garden I lose many a young milkweed shoot to black stem weevils. The milkweed never recover and I end up losing the plant (I’m guessing because they expending energy to grow, and don’t have any new energy to regrow or come back next year). The weevils clip the tops of new shoots and they look just like your sunflower shots, sans blooms.
I’d be curious to know what, if any, specialized natural predators exist to control these types of weevils. For example, are there parasitic wasps that target the fallen blossoms to prey on the eggs/larvae, or nematodes or other soil predators that go after the larvae when they overwinter? Certainly a potentially rich food source for some other little critter that can take advantage of it.
I am equally curious Patrick! I don’t know the answers…
This happens a lot to Silphium here in Ks/Mo. I usually don’t see it happen as much to Helianthus. I just noticed it this past summer, and it took a while for me to catch one in the act. It seemed so horrible at first, but most plants seemed able to resprout and flower just fine afterwards.
It is common to see Helianthus mollis so decapitated here in Missouri and have thought it was caused either by insect or large herbivore. Does anyone know if pale prairie coneflowers and other Echaneous species are susceptible. Many have blamed cattle or deer but maybe the critter is much smaller. I’ll try to be vigilant for a weevil.
I’ve never seen Echinacea affected in this manner but Helianthus yes! I saw it a lot this year and Chris thank you so much for posting this. I’ve often wondered but not worried about it because it never causes too much loss even in our seed production plots. If I were more production oriented I wonder if mowing the plant high to delay flower development would reduce this pest?
Your post reminds me of the one and only prairie joke that I know told to me years ago by Ray Schulenberg which I will share with you now: There are two destructive weevils in the prairie – One weevil (Haplorhynchites aeneus) decapitates the heads of Silphiums, effectively preventing any seed production. The other weevil (Trichapion rostrum) feeds on the seeds within Baptisia pods, destroying many but usually sparing a few. So, you could say that the Baptisia weevil is the lesser of two weevils.
Love dsollenberger2013’s joke.
Thank you for the post. This was very helpful for me. New cut flower farmer in Northern Illinois. The weevils are really doing a number on my biggest, most valuable sunflowers. I have been just leaving the heads on the ground, but now I’ll do something different. Sanitation this year seems like it should help a lot next year, based on life cycle.
Thank you for this article. It took a lot of research a few years ago to identify the perpetrator! We have been taking quite a hit from the weevils over the past few years, specifically our purple coneflower and cup plant. We remove the hanging heads and dispose of the weevils, but we’ve not been able to do it enough to disrupt the cycle for the following year. Interestingly, the large area of purple coneflower in the neighbor’s yard across the street is unaffected. I’d welcome any info on natural predators for these critters.
These weevils have devastated the Arikara sunflowers in our native garden the last two years.
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I’ve been having issues with this weevil the last two years on my coneflowers, rudbeckia and sunflowers here in Ohio. Hoping to find some beneficial predators to help get rid of them.
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