Plants that dupe insects into performing sexual favors

Most flowering plants spend resources on rewards for pollinators like sugary nectar. Others don’t bother, and rely on trickery instead. The most hilarious form of this is sexual deception perpetrated by many orchid species. These plants create flowers that resemble female insects so strongly that male bees will hump them, picking up pollen in the process. One part of the trick is physical appearance. These flowers are often hairy and have patches of iridescent color like insect wings. However, the most important feature is scent. The flowers give off scents that are the same as those produced by female insects, except the flowers make more of them. The consequence is that a male bee would rather hump an orchid flower than mate with a female bee. The trick needs to be so good that it fools bees at least twice, once to pick up pollen and once to deposit it.

MichaelRWhitehead
Hammer orchid and male thynnine wasp. Image credit: Michael Whitehead.

If you enjoy slapstick humor, definitely check out some videos of male thynnine wasps and hammer orchids (see resources below). When male wasps try to grab what they think is a female wasp and make off with “her”, a hinged tether slams the wasp right into the reproductive part of the flower where pollen can be picked up and collected. Male wasps will actually bash their heads on the flower multiple times before realizing that something has gone wrong. While this may seem incredibly dimwitted, it is hard to blame the wasps; this orchid produces 10 times as much pheromone as female wasps. These are some incredibly sexy fakes.

There are downsides to this method for the orchids as well as the insects. Orchids employing this technique must specialize on a species that resembles the flowers in appearance and scent. If the local population of that species takes a hit, there are no other insects around who can be fooled by the flowers and the orchids will have difficulty reproducing. In addition, the orchids can never become too abundant in any given place because enough male insects must actually mate with real female insects in order to sustain the pollinator population.

While it is easy to have a laugh at the male insects, female insects can be just as gullible. Rather than looking for a good lay, however, female insects tend to be very interested in finding good places to lay their eggs. And to a fly, what better place to build a nursery than a steaming pile of poo or a stinky animal carcass? You might be surprised how great a strategy mimicking poop and dead animals can be for plants. It has independently emerged as a trait in a wide variety of plant lineages. These are just a few of my favorites.

US Botanical Garden
Titan arum. Image credit: US Botanical Garden.

Titan arums (Amorphophallus titanum) produce some of the world’s largest flowers, up to a meter in circumference and over 3 meters tall. Not only do they stink of rotting meat, but the inflorescences are heated to both better spread the scent and also more closely resemble a freshly dead animal.

WikipediaUserGilbert8888
Starfish plant. Image credit: Wikipedia user Gilbert8888

The starfish plant, Stapelia gigantae, is a succulent member of the milkweed family that looks like hide peeling back from a torn carcass and also stinks of putrefaction. The California Dutchman’s pipe, Aristolochia californica, is a member of the birthwort family and befuddles fungus gnats that get lost in their pitcher-shaped flowers until they eventually escape, taking pollen with them.

Carina I ispotnature.org user
Satyrium pumilum. Image credit: ispotnature.org user Carina I

You are probably not surprised that orchids are also into this game. If you take a drive in South Africa, you can see flies flocking to dead animals at the side of the road that are laden with the pollen sacs of the orchid Satyrium pumilum. It’s a beautiful flower, especially if you love the main botanical character from Little Shop of Horrors. Even other kingdoms of life profit from this charade. Fungi like stinkhorn mushrooms use a combination of nasty odor, texture, and color to trick flies into picking up their spores.

 

Speaking of plants making things that look like poop, the Cape restio (Ceratocaryum argenteum) produces nuts that look and smell like a ball of poo. This tricks dung beetles into rolling them off and burying them, even though there is no place for them to lay their eggs.

 

Feature image by N. J. Vereecken.  See a video here.

 

Resources:

A classic video by David Attenborough of the BBC on sexually deceptive orchids (https://www.youtube.com/watch?v=-h8I3cqpgnA)

Whitehead, M.R. (2016). Sex, lies and pollination. Australia’s remarkable sexual swindlers. Available at: https://michaelrwhitehead.wordpress.com/2016/03/30/sex-lies-and-pollination-australias-remarkable-sexual-swindlers/

Sexual Encounters of the Floral Kind, a video describing the interaction between hammer orchids and male thynnine wasps (https://www.youtube.com/watch?v=Hv4n85-SqxQ)

This is a shorter video showing what male thynnine wasps are attempting to do, and what happens when they are tricked (https://www.youtube.com/watch?v=mNf9lp9EXHc)

Want to learn about more plant species that resemble dead animals? Have a look at this article by C. Wrey from Listverse (http://listverse.com/2011/05/30/top-10-amazing-carrion-plants/)

A popular science article published by L. Murray at Earth Times (http://www.earthtimes.org/nature/death-key-sex-life-orchid/461/) describes this paper by van der Niet, T., Hansen, D. M., & Johnson, S. D. (2011). Carrion mimicry in a South African orchid: flowers attract a narrow subset of the fly assemblage on animal carcasses. Annals of botany, mcr048.

A popular science article published by the University of Cape Town (https://www.uct.ac.za/dailynews/archives/?id=9392) describes this paper by Midgley, J. J., White, J. D., Johnson, S. D., & Bronner, G. N. (2015). Faecal mimicry by seeds ensures dispersal by dung beetles. Nature plants, 1: 15141.

 

 

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2 thoughts on “Plants that dupe insects into performing sexual favors

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  1. So the curious thing is that I know of many examples of wasps tricked by sexually deceptive flowers, but I can’t think of a single example of a male bee tricked in this way. Am I just oblivious or are bees more clever than their waspy counterparts?

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