Ted and Judy

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Carrion Flowered Succulents

Large buds and flowers of a carrion flowered succulent. Large (30cm) star-shaped flower with reddish tinge, and 15cm cone-shaped buds.
Stapelia plant with flowers and buds

Carrion flowered succulents are blessed with ornate flowers offset by the contrasting stench of decaying corpses. This “perfume” attracts a number of carrion flies that fall into two main groups: blow flies (Caliphoridae) and flesh flies (Sarcophagidae). While the stench puts off the average gardener the unusual structural forms and striking flowers attract collectors. These plants are natives of dry climates in Africa and India making them difficult to grow in humid environments. This is another reason for their presence mostly in specialist plant nurseries and collections.

Judy and I acquired our two species from our friends Tony and Katie Hiller at Mt Glorious just north of Brisbane. The plants have been growing vigorously for a number of years so our local conditions seem to suit them. The species we have are Stapelia gettliffei and Orbea variegata (Common Carrion Flower). Both are leafless succulents whose main stems collapse forming a ground cover with a scrambly growth form. The Hillers gave us a description of the flowers and perfume of both species, but we did not fully understand their beauty and “perfume” until we sampled them with our own eyes and noses.

Stapelia gettliffei

This African species has bulky four-sided, bright green stems with short incurved spines along each ridge. 

We repotted the plants on getting them home and they spent the next year or so putting on vegetative growth. One day we noticed small conical shaped buds on the Stapelia that expanded to an astonishing length of 15cm. We waited in anticipation for the buds to unfurl and were astonished once again by the 30cm diameter of the flowers and their very unusual form.

The flowers are star-shaped with five petals fringed with long fine white hairs. There are raised red, wavy lines running concentrically around the petals accompanied by a dense covering of short red hairs. The red lines are closely packed giving the surface of the flower a reddish appearance, the red intensifying towards the centre as the red lines become compressed. The other characteristic we liked about this and the Common Carrion Flower is their rotting corpse “perfume”. Our reasons for this are discussed below under Why I find Carrion Flower perfume so Attractive. The odour from these two species is not particularly strong in an outdoor setting compared to some stinkhorn fungi we found growing in our front garden a few tears ago. The latter was so strong we had to shut the front windows. That being so I wouldn’t recommend these two species as indoor plants. The smell is one thing and the flies another

Orbea variegata (Common Carrion Flower).

Another African species with a similar scrambly growth pattern, but the fleshy stems are smaller and closely overlapping. The flower is much smaller at 10cm diameter with five petals and an upraised central ring or annulus; a distinguishing feature of this genus. The colour is vivid maroon with variable white markings. 

The carrion odour of this species is less intense than that of Stapelia and seems to attract more flesh flies than blow flies. 

Why I find Carrion Flower Perfume so Attractive

The attraction of course is the flies; their form and behaviour. In the last week two Stapelia flowers emerged within a day of each other resulting in a cloud of carrion flies. The droning chorus of the flies as they rose in unison when disturbed and their beautiful metallic bodies shining in the sun is enough to gladden anyone’s heart. So if you are repelled by the habits of carrion flies put that to one side for a moment and appreciate their colours. The common blow fly species are metallic blues (blue bottles), green (green bottles) whose colours shine like Christmas decorations in the sun. Their red eyes contrast with the metallic bodies. I noticed two other species of blow flies, one very small and another with light brown abdomens showing a hint of light metallic green reflections. The flesh flies attracted to the flowers are largish with black and white longitudinal stripes on the thorax and a black and white checkerboard pattern on the abdomen. They also have contrasting red eyes and their bodies are covered with strong bristles. To my entomological eyes flesh flies are very attractive.

Now let’s consider the carrion odour. Obviously it is produced by the plants to attract flies for pollination, but the odour has an additional side interaction. If you stick your nose close to the flower you instantly recognise the complex odours of a decaying corpse with the hint of ammonia based compounds. It is these ammonia based compounds that trigger egg-laying behaviour in the flies. In the Stapelia flowers large numbers of fly eggs were laid around the entre of the flower. You might think these eggs were wasted but nature wastes nothing. By the end of the day small black ants moved in and were harvesting the eggs.

Forensic Entomology

Carrion fly behaviours and life cycles are proving of great use in calculating the post-mortem Index (time elapsed from death) of corpses. This emerging science is called Forensic Entomology and with ongoing research is gaining a reliable reputation in criminal investigations. 

Many insect groups (beetles, flies, ants) and mites are attracted to corpses: some feeding on the decaying flesh; some as predators feeding on fly larvae or eggs; and some for shelter. The most important for forensic purposes are the flies. Using these investigators can tell fairly closely if the corpse has been moved, the time from death and the presence of drugs or poisons in the corpse by testing the body fluids of the fly larvae. Some beetles feed on the fly larvae, others on the decaying flesh. The beetle family Silphidae (Carrion Beetles) bring mites with them that hitch a ride on their bodies. Once they arrive at a corpse the mites abandon ship in search of fly eggs. Ants forage for fly eggs and larvae. Small insects such as springtails (Collembola) use corpses for shelter. From this you can see that corpses develop complex ecosystems of their own and very little of a corpse remains unused (bones and teeth). This is a very brief overview of the interesting science of Forensic Entomology but if you want to read more a short easy to read introduction occurs at this link.

In the last paragraph I mentioned mites hitching a ride on carrion beetles. This process is called Phoresy and there are numerous examples of complex relationships accompanying this behaviour. A short discussion on Phoresy is available at HHS.

Well this post started out discussing flowers and ended up talking about corpses and Phoresy, which indicates how connected and complex relationships are in nature. Please give the links a look as they add more detail to this interesting story. Enjoy.

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