Georgia: Rearing the American Shieldback, Atlanticus americanus

DisclaimerThis has been my first experience keeping any members of this genus.

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Adult male American shieldback, Atlanticus americanus. Reared from nymph collected in Eatonton, GA.

A group of katydids that has consistently eluded me throughout the years is the shieldback katydids (subfamily Tettigoniinae). These tend to be large, bulky, dark-colored, and predacious species. For many years, the only one I had ever seen was the Roesel’s katydid, Roeseliana roeselii, an introduced European species found in the northeastern U.S. Almost all other U.S. shieldbacks live in the west, but there is a single widespread eastern genus, Atlanticus, plus a rarely seen southeastern specialty, Hubbelia marginifera (more here). I always wanted to see Atlanticus, as they present a very different image than more typical leafy-looking katydids. My wish was finally fulfilled in August 2014 when I ran across a single old male of Atlanticus testaceus in Delaware. However, I was not able to enjoy his presence long, as he died within a few days. This March, while in Georgia, I was thrilled to find that our campground was brimming with tiny shieldback nymphs, only a few millimeters each! They were abundant in the leaf litter of the forest surrounding Lake Sinclair. I captured as many as I could, but since I had limited space, I was forced to cram them all into a single large container. I knew that these could cannibalize, but hoped that at least some of them would make it back alive.

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Part of the original group of tiny shieldback nymphs. 

My fears were confirmed when I arrived back in Ithaca and sorted out the catch. Out of about 15 originally, only 6 had survived, and those individuals were fat on the meat of their brethren. I immediately separated them out into their own containers to prevent any more cannibalism. They seemed to adjust well to their new quarters and fed avidly on carrots and fish flakes, my standard orthopteran diet.

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One of the baby shieldbacks. 

I learned quickly that the shieldbacks were experts at molting in cramped conditions, unlike most katydids. They molted fine in their original small containers all the way up to their final nymphal instars. By this point, I had discerned an ovipositor on only one individual, meaning that I had 5 male nymphs and 1 female nymph. They were large enough that I began to supplement their diets with live prey (mostly small leafhoppers and moths caught locally), which they actively hunted down and ate. Once each shieldback started showing signs of getting ready to molt, I transferred them to a large container with a standing piece of corkbark for the imaginal molt. This worked perfectly, and although one of the male nymphs died unexpectedly from unknown reasons, all the rest became adults over the course of about a month.

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The largest male nymph, shortly before becoming an adult. 

When the first male nymph became an adult, I was able to key him out to Atlanticus americanus using a paper by Rehn and Hebard (1916). As adults, they became much more aggressive and predatory. Touching their antennae with forceps caused them to leap forward and start biting whatever was in front of them. On several occasions that turned out to be my finger, and I learned that they have powerful bites indeed. Unlike many other predatory animals such as spiders or assassin bugs, shieldbacks have no venom to quickly kill their prey. Instead, they rely on strong, fast bites to incapacitate their quarries. It was interesting to watch their strategies on various insect species. With smaller, weaker animals such as leafhoppers or caterpillars, they would simply grab the insect and start eating. With larger, more active prey, they would grab and attempt to start eating, but as soon as the prey started kicking and struggling to escape, the shieldbacks would systematically move up the body of the prey, biting at intervals until the insect stopped moving. Only then would the predator continue its meal.

In contrast to their dietary habits, I found their songs to be very peaceful and gentle. Two of the males have recently begun to sing. Their call is a series of soft, brief buzzes, repeated about a dozen times. They usually start singing at dusk and continue into the night. Fascinating that such a fierce predator would have such a tranquil voice.

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The single adult female shieldback. 

Reference:

Rehn, J. A., & Hebard, M. (1916). Studies in American Tettigoniidae (Orthoptera). VII. A Revision of the Species of the Genus Atlanticus (Decticinae). Transactions of the American Entomological Society (1890-), 42(1), 33-99.

 

Addendum: I originally wrote this post a few weeks ago and for some reason never got around to actually putting it up on the blog until now. All of my 5 shieldbacks are still alive and well, and the 4 males sing every night. Each tends to spur the others to sing, so that their buzzing becomes blended, and the chorus continues for well over the time span of a single male’s song. I can only imagine what it sounds like right now in their native home of Eatonton, Georgia.