Just Mimics or Something Much More? – The Orchid Mantis (Hymenopus coronatus)

Ever since it was first discovered by late-19^th century explorers in the forests of Indonesia, the orchid mantis (or Hymenopus coronatus) has captured the imagination of experienced ecologist and novice insect collectors alike. ¹

While orchid mantises, like other praying mantises in the insect order Mantodea, are a generalist predator that uses its long, raptorial legs to seize unsuspecting prey, their distinctive coloration and morphology gives rise to a relatively unique style of hunting.¹¹

Instead of sporting a natural green and brown color to blend into its surroundings, orchid mantises stand out from the foliage with its bright white body complete with hints of pink and yellow hues. ⁸ This combined with its broad abdomen and petal-like exoskeleton extensions on four of its legs, known as femoral lobes, allows the mantis to look – at least to the human eye – like an orchid flower. ^6,7

But are they mimicking the flowers to attract pollinators for food?

More to the point, do they even look like flowers to other insects?

Surprisingly, while H. coronatus has for years been the go-to example for deceptive mimicry in action, relatively little has been studied about the insect. In fact, most of the information we know about them seems to come from a few anecdotal accounts by Arthur Russell Wallace, a prominent evolutionary theorist, and a single 1899 observation of the insect! ⁸

Believe it or not, it wasn’t until 2013 that the first paper describing the distinctive characteristics of the orchid mantis in scientific detail was published! ⁸

In a groundbreaking paper exploring H. coronatus, Dr. James C. O’Hanlon and his team examined dozens of orchid mantises using spectral reflections and digital scans to quantify their color and femoral lobe shape.⁸

All of the mantises tested showed a primarily white signal that was UV-absorbing. While some differences in individual hue were observed, the results were below a “discrimination threshold” that researchers applied, which took into consideration other confounding factors like lighting conditions.⁸ The insect’s lobe shape varied slightly both between and within individuals, though not enough to be considered significant. In short, while they may sometimes look different from each other, quantitatively speaking they’re more or less identical.⁸

Not satisfied with just a superficial description, the team went on to put several commonly held beliefs to the test, with surprising results!

Firstly, through habitat experiments, they supported the idea that H. coronatus are aggressive mimics which actively lures prey to themselves, a bit like an angler fish with its glowing “lure”, rather than cryptically hiding among similarly colored flowers to catch unaware pollinators. ⁶

However, the insect it actually doesn’t closely resemble any known species of orchid.

Instead, the orchid mantis actually attracts pollinators to itself BETTER than real flowers!⁷

How?

One theory suggests that because orchid mantises consume a wide range of insects, they may have evolved to mimic generalized “flower-like” stimuli, such as symmetry and bright coloration which reflects UV light, rather than mimic a specific flower whose pollinators may be constrained to a specific region or habitat. ⁵

And those petal-like extensions that often fool us?

Their studies show that even with the extensions removed or held at unnatural positions, no significant change in prey capture was seen, suggesting that it’s color not “petal” shape attracts the insects. ^6,7 So perhaps the features are used to avoid predators with more complex eyesight, as they are virtually indistinguishable from flowers to different bird visualization models?⁷ Maybe they are mechanism for tricking pollinators up close, after the prey have been lured in by the mantis’ alluring color?⁶ Or it could just be a way for the mantis to increase its surface area so that it can be spotted from afar by potential prey.⁷

Truthfully, scientists aren’t quite sure of the answer at the moment…

Indeed, it seems that the more we look into the species, the more we find left to discover and study!

Visual cues may just represent one of the many ways H. coronatus trick their prey.⁸

After noticing that juvenile orchid mantises seem to have more success catching oriental honeybees (Apis cerana) than their adult counterparts, Dr. Takafumi Mizuno and his team set out to see if something else was helping them lure the bees.⁴

Turns out the juveniles release volatile chemicals from their mouth parts that are also used by the bees for communication, which not only gives juveniles a second form of aggressive mimicry but also attracts the bees head-on to the mantis, directly toward its raptorial limbs!⁴

What about repelling unwanted predators who might want to snack on the mantises before they grow to their flower-like color, size and morphology?

Well, insect keepers have noted that in the short span of time between when they hatch out of its egg case (or ootheca) and when they molt for the first time, the color of H. coronatus is vastly different from when they are juveniles or adults. ^1,2,3 During this stage, also known as the insect’s first instar, the young mantises are bright red and appear to “walk” on all six of their legs, which are black in color!³

Once again, while observation data has repeatedly confirmed this occurrence in captivity and researchers have suggested that they are mimicking undesirable insects such as Assassin bugs (in the family Reduviidae), the hypothesis has never been experimentally tested.¹

H. coronatus might even be the gateway species that changes how we view common arthropod phenomenon such as sexual size dimorphism, where the females of a species are much larger in size than the males.

Previously, it was assumed that the difference was exclusively to help with female reproductive success, as in general “the larger the female, the [more] offspring”. ⁹ However, a phylogenetic study by Dr. Gavin J. Svenson and his team show that – at least in the case of H. coronatus – predatory success and niche exploitation based on sex may have cause the females to become much larger to mimic flowers more closely and take on larger prey, while the males remained smaller to help with finding a mate without alerting potential predators.⁹

 In short, as charismatic and captivating H. cornonatus may be, they remain critically understudied.

Far beyond “just pretending to be an orchid”, numerous papers published in the last few years point to a complex relationship between an orchid mantis’ age and sex which radically alters its behavior, survival and hunting strategy.

So the next time you hear another fascinating story or observe some compelling behavior in insects, don’t be satisfied with the first thing that pops up on the internet. Instead, take a second to look deeper into the scientific literature.

You may just discover that you are delving into a whole new world of knowledge that’s just waiting to be explored.

Remember: looks can be deceiving, so never judge a book by its cover… or in this case, a bug by its color!

 

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References:

1. Gurney, A. B. (1950). Praying Mantids of the United States, Native and Introduced. Annual Report of the Board of Regents of the Smithsonian Institution. The Smithsonian Institution. 105: 344–345.

2. Linda, M. (2017). Orchid Mantis. Retrieved October 16, 2018, from https://www.keepinginsects.com/praying-mantis/species/orchid-mantis/

3. Menth, L. (2015). A Deceptive Flower – Malaysian Orchid Mantis. Retrieved October 18, 2018, from https://creaturefacts.wordpress.com/2015/06/

4. Mizuno, T., Yamaguchi, S., Yamamoto, I., Yamaoka, R., & Akino, T. (2014). “Double-Trick” Visual and Chemical Mimicry by the Juvenile Orchid Mantis Hymenopus coronatus used in Predation of the Oriental Honeybee Apis cerana. Zoological Science, 31(12), 795-801. doi:10.2108/zs140126

5. O’Hanlon, J. C., Herberstein, M. E., & Holwell, G. I. (2014). Habitat selection in a deceptive predator: Maximizing resource availability and signal efficacy. Behavioral Ecology, 26(1), 194-199. doi:10.1093/beheco/aru179

6. O’Hanlon, J.C., Holwell, G.I, Herberstein, M.E. (2013) Pollinator deception in the orchid mantis. The American Naturalist 183(1): 126-132. https://doi.org/10.1086/673858

7. O’Hanlon, J.C., Holwell, G. I., & Herberstein, M. (2014). Predatory pollinator deception: Does the orchid mantis resemble a model species? Current Zoology, 60(1), 90-103. doi:10.1093/czoolo/60.1.90

8. O’Hanlon, J.C., Li, D., & Norma-Rashid, Y. (2013). Coloration and Morphology of the Orchid Mantis Hymenopus coronatus (Mantodea: Hymenopodidae). Journal of Orthoptera Research, 22(1), 35-44. doi:10.1665/034.022.0106

9. Svenson, G. J., Brannoch, S. K., Rodrigues, H. M., O’Hanlon, J. C., & Wieland, F. (2016). Selection for predation, not female fecundity, explains sexual size dimorphism in the orchid mantises. Scientific Reports, 6(1). doi:10.1038/srep37753

10. Wipfler, B., Wieland, F., Decarlo, F., & Hörnschemeyer, T. (2012). Cephalic morphology of Hymenopus coronatus (Insecta: Mantodea) and its phylogenetic implications. Arthropod Structure & Development, 41(1), 87-100. doi:10.1016/j.asd.2011.06.005

Image resources:

1. Giudici, A. (2014). Orchid Mantis.  Retrieved October 24, 2018, from https://flic.kr/p/nvouEF
2. Thomas, S. (2009) 1^st instar Hymenopus cornatus Retrieved October 24, 2018, from https://flic.kr/p/6aUVcK