Scent of seduction

With the flowering of our titan arum for the third time this summer minds have been turning to how we can help our plant, fondly called New Reekie, to reproduce. As is the case for most plants this means pollination.

New Reekie with dramatic lighting around midnight on 23 June.

New Reekie is an example of what is called a carrion flower, which means the flower mimics the appearance and scent of a decaying animal corpse in order to attract specialist flies and beetles that feed and breed on dead bodies. These insects have to be strong fliers as the crucial resource that they rely on is generally rather thin on the ground. They also have a finely tuned and sensitive sense of smell.

Arisaema is another carrion flower in the same family as titan arum.

This specialisation in the pollination of titan arum has inspired us to carry out a simple experiment using local carrion insects that are commonly found in Scotland to see if they find the scent of New Reekie seductive.

Captured blowflies were held in a fabric cage prior to release.

Working with colleagues at the National Museums Scotland a plan was made to capture and mark blowflies, a common carrion fly that is active for a large part of the year. This is easily done with traps containing rotting fish or meat. These marked flies were then released into the glasshouse where New Reekie was blooming at 9pm on the first night of opening (23 June). The timing was important because titan arum plants are at their most smelly on the first night. At this point the plants female parts are receptive and insects with a covering of pollen arriving from another titan is what the plant needs to attract.

Prior to release all the blowflies were marked.

With much fanfare and excitement the blowflies were released and both visitors and staff were asked to watch New Reekie for the first arrival. Advanced voting on how long it might take a fly to arrive was very optimistic about a rapid appearance: 59 (38%) thought less than a minute; 67 (43%) thought less than five minutes; 19 (12%) thought less than ten minutes and only 10 (7%) of the people who voted thought it would take more than ten minutes.

Entomologists from the National Museums Scotland trying to spot blowflies.

Despite all the optimism the flies were never seen again. Why this was is just a matter of speculation (flies are not generally active at night, the smell gradient might not be so obvious in an enclosed space or perhaps it was simply a bad match). One gruesome explanation is that the insect eating plants nearby were well fed that night!

It’s worth remembering that negative results are still results and they lead to new questions that can be tested in further experiments.

However, the real icing on the cake for this particular line of enquiry was a significant discovery the morning after the blowfly experiment. At around midnight on 23 June a hole was cut in the side of New Reekie to allow access for hand pollination with pollen provided by the Eden Project. When the plug was removed the following morning by some staff inspecting their handiwork a large and very active black beetle was found inside New Reekie’s hidden floral chamber. Ashleigh Whiffin, entomologist at the National Museums Scotland, identified it as the carrion beetle Necrodes littoralis. This native insect is particularly associated with the coast where the dead bodies of seabirds and other marine life washes up.

Female Necrodes littoralis caught inside the titan arum on 24 June. Image copyright the National Museums Scotland.

Even though our experiment showed no evidence for the attractiveness of New Reekie’s smell to blowflies, it is really remarkable that a local carrion beetle found the smell irresistible. Proof positive of the strength of the attraction provided by the plant and its effective mimicry of a decomposing body. The determined beetle had to find a way inside an enclosed space when all the air vents were shut. To do this it must either have found a crack somewhere, or come in the same way as the 400 visitors who saw New Reekie on the first night of flowering.

Male Necrodes littoralis showing the impressive antennae with scent detectors that enable carrion to be located from some considerable distance. Image copyright the National Museums Scotland.

This native carrion beetle is in the same group as carrion beetles that have been found inside titan arum in its native home of Sumatra in Indonesia. This really is a quite remarkable result and could be the first time that carrion beetles have been observed being attracted to the titan arum outside of Indonesia. Well done New Reekie for managing to entice a Scottish beetle into doing your bidding. Perhaps the beetle has helped to spread the pollen that was so carefully introduced by staff at the Garden?

The beetle was given its freedom, but the record of it from New Reekie will be sent to a project recording carrion beetles in the UK: The National Silphidae Recording Scheme.

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1 Comment

  1. Gary Smith

    Incedible flower.

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