Dead Horse Arum

Image: emmapatsie via Flickr
Helicodiceros muscivorus

I love flesh-mimicking flowers! Things that blur boundaries are often interesting, but one would think that the plant/animal divide would be an extremely strong one. Not so much a picket fence as a 3 foot thick, lead wall.

Then you see something like the Dead Horse Arum and you realise that an animal's body is an object in the environment that a plant may want to mimic. They just need a reason to do it. Why on earth would a flower do well to look like a corpse? Let alone what appears to be the back-end of a corpse.

The answer is reproduction, of course! While other flowers attract pollinating insects with colours and nectar, the Dead Horse Arum has found a way to attract pollinating blowflies without paying a thing for their troubles.

This plant from the northwestern part of the Mediterranean indulges in pure exploitation.

Image: Barry Rice

You begin to see the ruse with little more than a glance. The spathe is effectively covered in fur and already looks like a huge slice of pepperoni. It's a good start, but mere appearance is not enough.

The long, finger thing that looks like a hairy tail is the spadix, and it produces a scent that smells akin to a rotting corpse. This alone will attract blowflies from all around.

For the Dead Horse Arum, step one is complete. They have another trick up their sleeve to fine-tune the behaviour of the blowflies and get them right where they want them.

The key is that the spadix produces not just a scent, but heat as well. In one study, they were an average of 12.4 °C (54.3 °F) above ambient temperature and some peaked at almost 20 °C (68 °F) above ambient. This turns the spadix into an object of particular interest to the blowflies, and a pathway to imprisonment.

Crawling along the spadix, the blowfly enters the dark, tunnel of foreboding. They probably expect rot, filth and nastiness, all the hallmarks of high quality feeding and breeding grounds. Instead, the spathe narrows around the spadix to form a bottle neck. Squeezing through, the blowfly enters a chamber where female flowers lie waiting. Spines stop the blowfly from getting out.

Image: Barry Rice

The hope is that the imprisoned blowfly has recently left another Dead Horse Arum and has brought some pollen along. The blowfly struggles to get out all day, pollinating lots of flowers in the process.

The blowfly is trapped overnight. By morning, the female flowers will no longer be receptive, the male flowers will bloom and the spines will wither.

Only now can the blowfly escape, taking a dusting of pollen with it and hopefully flying straight to yet another dastardly Dead Horse Arum to repeat the process.

What a world we live in. You can't even trust a horse's arse these days!