Photo of the Week – July 13, 2018

You know how you can look at something for years and still not see every aspect of it?  I was walking through Lincoln Creek Prairie this week, stretching my legs after photographing for my square meter project, when I came upon a couple big patches of Illinois tick clover (Desmodium illinoense).  There weren’t any active flowers on the plants, and I was about ready to move on after just a quick glance when I spotted something white along one of the stems.  Upon a closer look, I could see it was a moth, and it seemed to be plastered up against the plant.

This white moth seemed to be stuck on the stem of this Illinois tick clover plant.

As I inspected the moth more closely, it was clearly dead, and appeared to be essentially glued to the stem.

Here is the same moth, photographed from a different angle. Here you can see the abdomen stuck to the stem, and the mess it apparently made as it struggled to escape.

Now, I’ve known that tick clover plants (and especially their seeds) can be sticky, but I always ascribed that to the tiny stiff (and sometimes hooked) hairs covering them.  I sure wouldn’t have thought those hairs could catch and hold an insect.  However, as I looked more closely at the hairs on this plant, there were little tiny droplets of clear sticky fluid at the tip of each hair.  How can I have spent 25 years or more looking at prairie plants and not noticed that?  I looked online and in my copy of the Flora of Nebraska book and didn’t find any reference to those droplets in either place, but surely other people know of this.  I’ll have to look harder.  In the meantime…

…as I looked at nearby plants, I saw lots more dead or dying insects glued to them.  The most common of those were lightning bugs, followed by Japanese beetles.

Lightning bugs were the most abundant of the insects I found stuck to tick clover stems. I must have seen at least 20 within a few minutes.
Japanese beetles (invasive species) were also a common victim of the sticky tick clover plants. This one appeared to have become stuck on a leaf, so I guess it’s not just the stems that have adhesive qualities.

I’ve written before about insects getting stuck to the bracts beneath thistle flowers and discussed the possibility that the sticky bracts helped keep ants and other non-flying nectar thieves from stealing floral resources.  Do tick clovers do the same thing?  If so, why haven’t I noticed?

This little gnat (midge? something else? I can’t see the antennae) was the smallest insect victim I found.  If you click on this photo you can zoom in and see the droplets on the tips of the hairs.
This mosquito lost its life when it apparently tried to take a rest break on this tick clover plant.
This picture-winged fly was still struggling when I found it.

I’m really curious to know if others have noticed insects losing their lives to tick clover plants, and whether or not it happens with other Desmodium species.  Does the plant produce the sticky droplets of liquid throughout its growth period, or just when it is flowering?  WHAT IS GOING ON HERE?

Thanks for any help.

8 thoughts on “Photo of the Week – July 13, 2018

  1. thesliceiconic July 13, 2018 / 2:41 pm

    Did you try to touch it? If so, how hard was it to get your finger back?

  2. Katharine Hogan July 13, 2018 / 2:58 pm

    Chris, I could have told you that tick clover plants are really sticky… ;D

  3. nigel64 July 13, 2018 / 3:19 pm

    Amazing, the harder we look the more questions we need answering. Great observation Chris. I’m now looking forward to summer as I touched an (unknown) plant last year (maybe a Galium) with tiny hairs that also felt sticky

  4. Marian Whitcomb July 14, 2018 / 10:47 am

    Time to write a paper Chris.

  5. Karen H. July 14, 2018 / 3:48 pm

    I read somewhere (and I don’t remember where) That this is theorized as an adaptation for plants to add nutrition to the soil around their roots. I will have to see if I can find the paper.

  6. Jan Curry July 14, 2018 / 10:32 pm

    such great timing on this article! Just noticed this plant in Johnson County, Kansas, but was not sure of my I.D. Your description of the stickiness and insects made me go Ah Ha! Thanks!

  7. Jose July 16, 2018 / 12:45 pm

    Is there some way to remove the glue-like substance from some individuals and compare to see if there are benefits to this trait (less insect damage, growth, etc.)?

  8. Mitch Lettow July 18, 2018 / 3:04 pm

    Hi Chris! Mitch here from a local land trust in southwest Michigan (Southwest Michigan Land Conservancy). This reminds me of a story from a professor in insect behavior I met in graduate school. Do a little searching on “entemopathogenic fungi insect behavior” and you’ll find that, there is a fair bit of information on insects that often die on the tops of plants (or other elevated positions) after fungal species inside the insect host have matured and need to disperse spores. By crawling to the top of the plant, the insect is providing the best chance for spore dispersal of the fungus (highest, windiest). The fungus is actually controlling the behavior of the insect host! Very cool/spooky stuff. Anecdotally, we have seen the same thing occurring with grasshoppers at the tops of prairie grasses in summer in some of our tallgrass prairie reconstructions. Here’s a good link to get you started:

    Could it be this?


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