Monday afternoon, I looked out my window and noticed the sky was covered by a combination of diffuse clouds and some hazy smoke, creating some beautiful soft lighting. The wind was light too, so I was obligated (OBLIGATED) to stop working on other projects and take my camera out for a walk. I mean, whaddya gonna do?
I headed across town to Lincoln Creek Prairie and spent a pleasant hour with flowers and inverts. During that time, I spent quite a while watching one particular butterfly milkweed plant. A small wasp was intent on feeding from the flowers and would repeatedly forage for a while, fly off a few feet, and then return. There was also a lynx spider hanging around on the same set of flowers and it looked to me like the two might run into each other eventually.
The other reason I stayed with the scene is that I was trying to figure out what, exactly, the wasp was doing. Normally, when I see insects feeding on milkweed flowers, they seem to be extracting nectar from the tops of the flowers. This wasp was focusing very intently near the bottoms of the flowers. It would approach a flower and cling to it for a few seconds before moving to the next. Even through my macro lens, I couldn’t quite tell what it was up to, but I assumed it was accessing nectar.
This made me realize that I don’t actually know exactly where the nectar is stored in a milkweed flower or what openings might exist from which hungry invertebrates can extract it. I tried to find diagrams online but didn’t have any luck. Any milkweed flower anatomy experts out there? I’m guessing this wasp was chewing through the flower to get to the nectar, but that’s just guesswork since I don’t even know where the nectar was!
Regardless, the meeting of spider and wasp did eventually occur, but nothing very exciting happened. The wasp seemed to ignore the spider and nudged it a little (accidentally?) as it moved between flowers. The spider seemed a little startled, but didn’t try to attack the wasp – it just scooted itself over a smidge and both went on with their lives. I guess the wasp, which was about the same size as the spider, didn’t fit the spider’s profile for a prospective meal. Fair enough.
A few minutes after I left that butterfly milkweed plant, I stopped at another and photographed the stilt bug shown below. I don’t have any other stories to tell about the stilt bug. It was just sitting in a way that was photogenic and it let me get close enough to photograph it. I liked the photo, so I threw it into this post. How about that for an anticlimactic end to this post?
The Prairie Ecologist 
I think the nectar location expert for the milkweed flower WAS the wasp. :)
You made me curious as I’ve photographed but not actually studied insects on milkweed flowers, in my case common which we encourage in our yard but I think the flowers all have the same characteristics. There is a slit near the bottom of the flower where they must insert their proboscis to obtain nectar. Since the wasp’s is shorter than a butterfly’s maybe it had to make more of an effort and was pushing its way in to get at it. I found this illustration that shows the anatomy. I’m not an expert but this seems likely. I just started following your blog and look forward to more from your explorations.
I think you’re right; stealing nectar without pollinating the flower.
Milkweed pollination is a whole evolutionary story. I love milkweed for many reasons but how it is pollinated is one of my favorites
Milkweed is a very complicated flower and it hides the copious amounts of nectar in a special place.
This is copied from a great article: Each flower has a calyx, corolla, and corona, which surround a central gynostegium. The gynostegium is formed from the fused, highly modified male (anthers and filaments) and female (stigmas and styles) floral parts. At the top of the gynostegium is a style-head, formed by fusion of the apices of two styles. The corolla is the outer and lower part of the flower and resembles petals (Figure 2). In some milkweed species the corolla is bent backwards (reflexed).
A B C
D
E
Figure 2. A top view of a showy milkweed flower showing the corolla (A), and the corona with five hoods (B), each with a prominent horn (C). A dark brown corpusculum (D) is visible at the top of three of the stigmatic slits (E).
The corona is the showy, upper part of the flower. Five hoods surround the corona and tempting pools of luscious nectar form at the base of each hood. In some species, each hood has a prominent horn. Together these slick, waxy floral structures manipulate the behavior of insects to manipulate the behavior of the insects to achieve pollination.
Click to access nvpmctn12764.pdf
Milkweed pollination is a whole evolutionary story. I love milkweed for many reasons but how it is pollinated is one of my favorites
Milkweed is a very complicated flower and it hides the copious amounts of nectar in a special place.
This is copied from a great article: Each flower has a calyx, corolla, and corona, which surround a central gynostegium. The gynostegium is formed from the fused, highly modified male (anthers and filaments) and female (stigmas and styles) floral parts. At the top of the gynostegium is a style-head, formed by fusion of the apices of two styles. The corolla is the outer and lower part of the flower and resembles petals (Figure 2). In some milkweed species the corolla is bent backwards (reflexed).
The corona is the showy, upper part of the flower. Five hoods surround the corona and tempting pools of luscious nectar form at the base of each hood. In some species, each hood has a prominent horn. Together these slick, waxy floral structures manipulate the behavior of insects to manipulate the behavior of the insects to achieve pollination.
Click to access nvpmctn12764.pdf
Thanks!
I thought your January 26, 2021 covered the pollinia, but not the nectar.
Hi! Great photos! Typically, pollinators sip nectar from the hoods, but the nectar also fills the gynostegium because nectar may be needed to facilitate pollen germination (a pollinium gets inserted into one of those stigmatic slits by a pollinator and the pollen tubes need to reach one of the two ovaries that are inside the gynostegium). If the wasp wasn’t chewing any holes, it might have just been accessing some nectar through the stigmatic slit.
Fun fact: all of the seeds in a single milkweed pod/fruit are often full siblings (i.e., all have the same “dad”), which is highly unusual among plants. One pollinium has enough pollen grains to fertilize all of the ovules in one ovary.
This is fantastic, thank you!
I love it. All the value milked from milkweeds on behalf of native plants and monarch butterflies and yet the most basic manner by which the flower confers this sweet value to all which benefit (human and not, organizations and businesses) is either unknown or, weirdly, is being withheld!
Who knows, maybe it is the sticky latex like sap not the assumed sugary substance?
Go for it! Might need a PI? Crowd source for ideas about the what, where, how, when, etc. of milkweed appeal to non-human visitors?
I jest – or do I? Chase
On Fri, Aug 6, 2021 at 9:22 AM The Prairie Ecologist wrote:
> Chris Helzer posted: ” Monday afternoon, I looked out my window and > noticed the sky was covered by a combination of diffuse clouds and some > hazy smoke, creating some beautiful soft lighting. The wind was light too, > so I was obligated (OBLIGATED) to stop working on other proje” >