Did you notice how, as humans, we sometimes have a morbid fascination for gory stories such as the one of Jack the Ripper, the infamous serial killer who removed the internal organs of his victims? Well, if you look close enough, you may also witness similar behaviours in nature, but for completely different reasons. The Chinese mantis, 𝘛𝘦𝘯𝘰𝘥𝘦𝘳𝘢 𝘴𝘪𝘯𝘦𝘯𝘴𝘪𝘴 Saussure, 1871, is probably one of the most widespread and abundant mantis species found in Asia, including in Hong Kong, but now also in the USA where it was introduced as early as 1896 and has since spread.
Just like other praying mantis, this species is a generalist predator that feeds on a variety of prey including numerous invertebrate species such as flies, crickets, bees, caterpillars, but also small vertebrates like the red-spotted newt. Some of these prey, however, are more difficult to digest than others. This is the case, for instance, of some caterpillars which acquire a toxicity in order to protect themselves. Let’s see how the Chinese mantis is able to cope and survive these deadly traps!
Caterpillars of the monarch butterfly, 𝘋𝘢𝘯𝘢𝘶𝘴 𝘱𝘭𝘦𝘹𝘪𝘱𝘱𝘶𝘴, are known to feed on milkweed plants that contain toxic compounds named cardenolides. The caterpillars will accumulate these toxins within their bodies to deter predators. However, not the Chinese mantis which were observed consuming these toxic caterpillars without any apparent ill effects. How can they achieve such a feat? The mantis were seen chewing open the caterpillars’ bodies, removing their midguts filled with plant materials, and only eating the remains. It seems that they evolved species behaviours to reduce exposure to the prey’s toxicity by removing the guts of monarch caterpillars. Sounds really clever, right?
Researchers discovered, however, that the mantis also performed the same gutting behavior on some other non-toxic caterpillars, so this behaviour did not appear to be specific to toxic prey. Moreover, the toxin concentrations in the consumed tissues and the removed guts of the monarch caterpillars are actually rather similar. Therefore, the mantis will still intake a lot of toxins by feeding on the caterpillars’ bodies. So, how can they survive the toxicity?
It was later confirmed that the toxic molecules cannot pass through the intestinal membrane of the Chinese mantis, so those are expelled instead of being assimilated by the organism. This allows the mantis to feed on toxic prey without being poisoned. But then how to explain the gutting behaviour observed in caterpillars if the mantis are not trying to avoid the toxins?
The response here is that the Chinese mantis are not trying to avoid the toxins contained within the caterpillars, but rather of the plant material contained within the gut of the prey. Mantis are carnivorous insects and their digestive systems are not adapted to degrade plant tissues and thus of the toxins contained within plant material. Ultimately, this is why Chinese mantises need to discard the plant materials by gutting the monarch caterpillars, or those could be lethal to them.
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Text: Arthur Lai
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