Plants are truly dynamic organisms. Even though most exist on a different time scale to that of the frenetic animal kingdom, their lives are filled with as much drama as the Serengeti or any tropical coral reef.
The Dead Horse Arum
Few plants are as arresting in appearance or behaviour as Helicodiceros muscivorus, the fabled Dead Horse Arum of the western Mediterranean. It is an aroid, a member of the large family that includes such popular houseplants as the Swiss cheese plant (Monstera) and the familiar European wild flower, the Cuckoo Pint (Arum maculatum).
Although they vary considerably in shape and size, most aroids are unmistakeable when in flower. A typical inflorescence consists of a modified leaf, the spathe, and an infamously phallic structure, the spadix, which carries tiny male and female flowers. These are often near the base of the spadix and in plants such as Helicodiceros, are enclosed in a chamber formed by the lower part of the spathe.
An Island "Paradise"
Perhaps "Dead Gull Arum" would be a more fitting name for Helicodiceros, because dead horses are seldom encountered on the uninhabited islets where they grow. Dead gulls, on the other hand, are rather more common because Helicodiceros grows near crowded, smelly seabird colonies which are generally littered with such aromatic delights as decaying fish offal and dead chicks.
Enter The Blow Fly
Although hardly a human concept of paradise, such places are a veritable heaven for insects of the genus Calliphoridae, better known as blow flies. During Spring, at the height of the seabird breeding season, these flies indulge in a festival of feasting and mating, utilizing every scrap of carrion as a nursery for their maggots.
When Is A Corpse Not A Corpse?
However, all is not as it seems, because Helicodiceros is about to stage a deception that can prove deadly to the blowflies´ offspring. During the winter, the plants have been growing steadily, producing distinctive complex foliage from tubers deeply rooted in rocky fissures.
Finally, the plant is ready to reveal its true splendour. It begins to sprout an enormous inflorescence, with a kink at the base so that it sits parallel to the ground.
Then, one sunny morning, the inflorescence opens wide to reveal a broad, leathery spathe covered with coarse reddish hairs, while jutting from the cavernous base of this is a long dark hairy spadix. The whole effect is remarkably like the decaying remains of an animal or bird, a resemblance that is not unintentional on the part of Helicodiceros.
Fatal Fragrance of the Helicodiceros
Not only is its appearance alarming, but the smell emanating from this formidable structure is wonderfully offensive too. Evocative of a rich cocktail of hot rubber, dung and rotting fish, this perfume is unlikely to be endorsed by many cosmetics companies but is exactly what it takes to draw in the plants´ intended customers, the flies.
On arrival, they crawl over the hairy spathe in search of that enticing aroma. Eventually, they find their way through the opening and into what appears to be the perfect place for raising the next generation - the interior of a corpse.
First, they pass through a ring of upward-pointing hairs, over the tiny and as yet unripe male flowers until they suddenly fall through a second ring of hairs and into the base of the chamber. Here they are trapped, but if they have already visited another Helicodiceros flower, any pollen adhering to their bodies is transferred to the receptive female flowers near the base of the spadix.
Escape
They are now trapped. Prevented from escaping by the smooth sides of the chamber and the jutting hairs, they might be imprisoned here overnight or for several days. During this time, some are so deluded by the smell and texture of the chamber that they lay their eggs - but when these hatch, the maggots are doomed to die of starvation.
Eventually, the entrapping hairs shrivel and the flies escape. During their captivity the female flowers have ceased to be receptive, but the males have ripened and now shed their sticky pollen, covering the insects with a fresh cargo. Many are promptly deceived into visiting another Helicodiceros, where they complete the task of cross-fertilization as intended by the aroid all along.
The Reptilian Connection of the Helicodiceros
On some islets in the Spanish Balearic archipelago where Helicodiceros grows, there lives a lizard called Podarcis lilfordi, the Lilford´s wall lizard. It is an inquisitive, omnivorous reptile and will happily eat everything from blow flies to bananas.
It also enjoys basking on the open spathes of Helicodiceros, especially in the morning. Many aroids, including the dead horse arum, are able to generate a significant amount of heat in their spadices through a metabolic process called thermogenesis.
This heat not only helps to disperse their perfume to attract flies even more effectively, it is also powerful enough to significantly warm the chilled bodies of lizards. As they absorb the aroids´ heat, the lizards are strategically positioned to feast on a steady stream of visiting blow flies.
With hungry wall lizards snapping up its potential pollinators, Helicodiceros may seem at a disadvantage. However, in recent decades the lizards have developed a taste for the fleshy fruits of the aroid and these they devour with relish. The seeds pass unharmed through the reptile's body and are deposited elsewhere, complete with a convenient measure of nutritious fertilizer.
As a consequence of this reptilian fruit fad, the dead horse arum has expanded its range and increased in numbers - truly, a superb example of behavioural evolution in progress and the ability of species to adapt and change over a remarkably short timescale.
References
Deni Bown: Aroids: Plants of the Arum Family Timber Press; Portland: 2000: ISBN 0 88192 485 7
Culture Sheet dot Org: Helicodiceros muscivorus
Peter Ashby - Peter Ashby lives near Granada in southern Spain, is an expert on natural history, and a dedicated traveller, writer and hispanist.
