Blogtober- Foul Odor

I usually think of flowers as lovely, sweet-smelling decorations. They’re actually plants’ reproductive organs, though, and some are distinctly weird. The fragrant, colorful ones like roses and asters attract bees and butterflies for pollination. However, other kinds of flowers are downright stinky, because they evolved to attract a whole different set of insects.

Skunk cabbage flower at Great Falls Park

Rather than courting bees and butterflies, these plants have a pollination partnership with carrion-loving flies. Thus their flowers smell rank, like rotting meat, and they may even also be a dark, meaty, burgundy color. Skunk cabbage, a carrion mimic in my area, blooms as early as February or even January. They’re able to do this because they even create enough heat to melt through any snow that might still be on the ground! Talk about a plant with superpowers.

Turns out this heat also is an attractant for carrion flies, helping spread the flowers’ foul fragrance. Actual rotting flesh creates heat too, so it’s yet another way the plants fool the flies. In addition to melting any snow, the warmth also helps waft the plants’ stench to hungry flies and beetles. Not all carrion mimic flowers occur in late winter, though, several bloom later in the spring or in summer. In fact, there are carrion mimics found in lots of plant families. Even beloved milkweeds! See https://www.cell.com/current-biology/pdf/S0960-9822(15)00881-7.pdf for a discussion of carrion mimic biology. Another flower that might be a carrion mimic is the Paw paw, whose maroon flowers appear in early March before the tree has sprouted any leaves. This flower doesn’t seem to stink very much, at least I never noticed it, so it may not be exclusively a carrion mimic. The color is certainly right though.

Paw paw flowers, photographed April 9, 2021.

Now, if carrion mimic flowers can melt through snow in order to bloom during the winter, how would their pollinators be still active? Turns out, carrion type flies can be active as soon as the weather warms just a bit. Different kinds of fly use different techniques for soverwintering: maybe they molted into pupal form before the cold hit, so they’re ready to finish on the first warmish day. Others are waiting in egg form ready to hatch into larvae; still other species spend the winter as adults by finding a warm protected shelter: inside your home, perhaps, or buried in a convenient compost pile. Flies also have a really fast turnaround from egg through larva, pupa, and finally adult. That means they can take advantage of even short winter thaws.

In fact, their fast life cycle is how police investigators can figure out how long a murder victim has been dead: knowing the general order of arrival for different insects, and how long each takes to go through the stages of metamorphosis, they can easily estimate how long a corpse has been available to carrion insects. If you’ve watched any of the CSI shows or other police procedurals, you might have seen this in action. In fact, real-life forensic scientists sometimes keep research fields studded with carrion, where they measure how long it takes for each insect to arrive and go through metamorphosis. Imagine how rank that must smell! All in the name of science, though.

Nature is weird, and disgusting, and totally fascinating. I may not want to sniff a bouquet of carrion-mimicking flowers, but I love that they exist.

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