Ask a Naturalist: Why are there dead bees on my milkweed plants?

June 02, 2020

Written by Mary K. Hanson

Photos and text by Mary K. Hanson, Certified California Naturalist 

Learn 

I don’t use insect repellant in my garden, so why am I seeing dead bees on my milkweed plants?

Near the Effie Yeaw Nature Center, you can see two species of milkweed plants: showy milkweed (Asclepias speciosa) with its large woolly leaves and intricate pink flowers, and narrowleaf milkweed (Asclepias fascicularis), a less ostentatious plant with thin leaves and much smaller blooms. 

Milkweed plants are interesting in that they have a variety of unusual boobytraps built into them that other plants do not. Besides their sticky latex (the white sap that drips from the plant when it is damaged) which can trap a variety of insects, the milkweed flowers themselves can also be dangerous for pollinators.  

Rather than offering up its pollen on upright visible structures called “stigmas”, the milkweed flower has its pollen hidden inside special little crevices called “stigmatic slits”. When a pollinator, like a honeybee, lands on the flower and walks over its surface to drink the flower’s nectar, the bee’s feet slip inside theses stigmatic slits.  Pollen inside the slit affixes itself to the bee’s feet, and when the bee moves to another flower, it carries that pollen with it. Transferring the pollen and putting its feet into the stigmatic slits of different milkweed flowers completes the process of pollination.

Occasionally, however, the bee’s foot may get caked in so much pollen that it simply cannot get its foot out of the slit. (Think of putting your hand into a jar with a narrow neck so you can grab a handful of candy at the bottom of the jar. Your candy-filled hand may then be so full and wide, it cannot get through the jar’s neck, and your hand gets stuck inside the jar.)  

Some bees actually amputate the trapped foot in order to escape. But if the bee is unable to do that and cannot manage to get its foot out of the stigmatic slit, it will eventually succumb to starvation and dehydration and die. We have seen this phenomenon on some of the plants around the nature center, and that may be what you’re seeing on your plants too.

In a future post, we will tell you about the trick monarch butterfly caterpillars use to protect themselves from being overwhelmed and suffocated by milkweed plant’s gooey latex boobytrap.  

Bee on milkweed flower

Here you can see a honeybee who was caught in the milkweed flower’s pollen boobytrap and was unable to escape.

 Bee with footstuck

Here you can see where the honeybee’s foot got trapped in the stigmatic slit.

Stigmatic slit of milkweed

This image shows you where the stigmatic slit is on the milkweed flower.

Create 

Flowers are made up of many different parts that form the reproductive part of flowering plants. They make the seeds! 

1) Discover these different parts of a flower here
2) Try drawing your own flower and labeling all the parts.

For younger kids, try drawing a plant and label all of its parts: roots, stems, leaves, flowers.

Activate  

Take a walk around your neighborhood and notice the type of flowers you see, and explore:

What colors do you see?
Are the flowers different shapes?
Are the stems tall or do they grow close to the ground?
Do they have a lot of leaves of just a few?
What pollinators are attracted to them?
Can you identify some of the plant or flower parts?