Mexican Bush Katydid Carnivory

Today when we went to check on our supposedly herbivorous Mexican Bush Katydids (Scudderia mexicana), we were shocked to find that one of the two had been completely eaten by the other!

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Most Orthoptera are herbivorous. At least, they usually are. Contrary to popular belief, almost all herbivorous animals are capable of carnivory during times in which plants are unavailable. Otherwise their meat-eating counterparts would never have evolved in the first place. For example, there are actually such thing as strictly carnivorous katydids and other Orthoptera that eat other insects and such. The Mexican Bush Katydid (Scudderia mexicana) is not one such example and are normally herbivorous.

So, we never expected that we would find one of our Mexican Bush Katydids happily devouring the cadaver of another katydid of the same species. . . .

As of two days ago, we still had two living Mexican Bush Katydids nymphs, both of which were wild-caught this year. The first one was much larger, at least one instar ahead of the other one. We had been keeping the two together in the same fruitfly bottle enclosure for as long as we have had them since there seemed to be enough space in there for such small nymphs.

But yesterday, the smaller one died a pretty horrible death. The thing must have been resting somewhere along the top of the container when the lid was not screwed closed. When we screwed the lid on not knowing that it was there, its abdomen got crushed very badly. The body was almost cut in two at the site of the injury with guts and body fluid trailing out of the wound. I guess it really would have made sense to remove the body at this time, but we didn't. We just left the poor thing crawl around frantically until it inevitably died from the injury by the end of the day. 

By today, however, the body was gone, but not because we took it out. It was completely missing with only a few scraps of the legs left at the bottom of the enclosure. The only logical conclusion we could make was that the other katydid have eaten the dead body! Boy, we were surprised. In the past, we had raised a larger number of Mexican Bush Katydids together in a tank where we had also witnessed some form of cannibalism in which the katydids would nibble at each other's legs and wings, often targeting victims that very recently molted. We had assumed that this was due to overcrowding and less-than-optimal living conditions since it is common for insects to eat each other when overcrowded. After all, we had even seen this happen in severely overcrowded, strictly herbivorous walking sticks too. However, overcrowding was not the case here as there were only two of them in a roomy enclosure. The other katydid must have simply took the rare opportunity to feast on a nice pack of fat and protein to supplement its normally leafy diet. 

After this, we begin to wonder that perhaps the particular species was, indeed, carnivorous to some extent in nature and normally scavenge for and feed on some small dead insects in the wild. Their closest Orthopteran relatives, the crickets, do this all the time. And perhaps by only feeding them an unvaried plant diet, we were depriving them of some nutrients and this was what may have actually encouraged cannibalism, and not any possible overcrowding. 

In any case, we decided to experiment. We have a hefty supply of fruitflies (Drosophila hydei) fruitflies that we regularly use to feed our European Mantises (Mantis religiosa) so we wanted to see whether the katydid would readily eat them as it had with its roommate. The procudure was simple. Basically, we just lightly crushed a fruitfly with a toothpick or our finger to kill it and draw out the liquid portions. Carefully, without causing alarm, we touched these liquid portions to the katydid's mouthparts to stimulate feeding, but did not forcibly feed the fly when it opened its jaws. 

What we found was that the katydid really did have an appetite for meat. It gobbled up four whole fruitflies in a row, effortlessly -- even more bestially than the much-touted praying mantis. Because insects do contain a lot of nutrients not available in plants such as chitin and animal protein (more variety of amino acids), we hoped that we had done the katydid a favor and it would grow to be healthier than the vegetarian katydids we had kept in the past. It's certainly nice to think it didn't just eat its roommate cadaver for nothing.

- Brian