The plant that turns a window into a lethal weapon

One of the most annoying sounds of summer is Thunk! Not a single Thunk! but the repetitive Thunk! Thunk! Thunk! of a fly repeatedly banging its head against a window. It doesn’t matter how much of a window you leave open, there’s always a fly that will bang its head against the window just for the joy of syncopated rhythm. If that irritates you as much as it does me, then you will love the cobra lily.

Cobra Lily
Cobra Lily, Darlingtonia californica. Photo by Brent Miller/Flickr

The cobra lily, Darlingtonia californica, doesn’t just have a cool name. It has windows, of a sort, and it uses them to deadly effect.

The name comes from the hood that the plant has. In the bottom of the hood is an opening and there’s a trail of nectar leading up there. What happens at the top? The prey tries to find a way out. You’d think the big hole in came in would make a perfect way out. However, the plant is sneaky.

Parts of the hood are translucent so the sun can shine through. Those same genes that guide the fly back into a window time and again are triggered by the plant. The insect will attempt to bang its head again the hood, again and again, to find a way out, ignoring the way it came in. After a while it tires, and then it becomes obvious that the cobra lily isn’t a lily after all.

It’s a pitcher plant.

This video from The Carnivorous Plant Whisperer on YouTube explains how the trap works from the insect’s point of view.


…and here it is in action with a fly wandering into the hood.


The sound will still annoy me. Yet I will have some satisfaction knowing that something is exploiting the fly’s habit.

About the author

Alun Salt

When he's not the web developer for AoB Blog, Alun Salt researches something that could be mistaken for the archaeology of science. His current research is about whether there's such a thing as scientific heritage and if there is how would you recognise it?