Curious and Curiouser: Tortoise Beetles Are Weird and Cool
August 1, 2020
With contributions from NMSU Extension Specialists Dr. Amanda Skidmore and Dr. Carol Sutherland (Entomology)
What kind of bug is this? It moves around the leaf like a Roomba vacuum cleaner.
- Gloria L., Albuquerque
(question originally posted to the Facebook group “Growing Food in and around Albuquerque & Foraging Too”)
I saw these critters for the first time on my tomatillo and tomato plants at home this week. I had noticed irregular-shaped holes in the tomatillo leaves but hadn’t taken the time to investigate. I knew I’d had grasshoppers nibbling at leaf edges throughout the garden, but these were holes in the middle of leaves, not at the margins. The critters seemed to have a shiny, almost iridescent shell. When I looked closer I saw lots of smaller, creepier creatures on nearby leaves that looked more like mites or an immature form of a scale insect with a black helmet that it waved at me while I was taking photos. I was intrigued, and this was just the beginning.
Not a half-hour later, I mentioned them and their irregular Swiss cheesy holes to a co-worker at the NMSU Agricultural Science Center at Los Lunas, and he said he had similar holes on his chile plants, so I took a look. Sure enough, we found the same shiny, shelled insects and the helmet-wavers too. I assumed they might be a type of scale in both the larval and adult form until one startled me by spreading its shell into wings and flying away.
That evening a person in an Albuquerque gardening group on Facebook posted a great pic of the same insect with a request for information. Another person offered “tortoise beetle” as an identification. I shared my photos and started a Google image search for “tortoise beetles.” The results were more entertaining than any Netflix show. Try it.
It turns out that tortoise beetles are known for getting crafty when making their shells and shields. Some make ornate armor out of plant tissues—search images for “palmetto tortoise beetle larva.” Many species, though, use their own feces to form bizarre protective structures. Yes, that’s right, those larval tortoise beetles I’d found were waving their poop umbrellas at me. Regular readers know I really love my job, and it’s precisely these kinds of experiences that invigorate me. And still, these tortoise beetles had more surprises up their…umbrellas.
I reached out to colleagues for more info on tortoise beetles in New Mexico and what I should do about them, if anything. NMSU Extension Integrated Pest Management (IPM) Specialist Dr. Amanda Skidmore offered, “In the Midwest, they are mostly found on wild Solanaceae plants [including potatoes, tomatoes, tomatillos, eggplant, and chiles] and not in the garden. The larvae are pretty crazy looking, and their ‘shell’ is actually their frass they are using as protection. The adults of this species even look like they have a tortoise on their backs. As for management in the home garden, hand-picking them off and dropping them in a bowl of soapy water is probably the best option. From what I have read, they will be focused on the leaves, not the fruit, so mature, healthy plants should be able to tolerate the feeding damage.”
Dr. Carol Sutherland, NMSU Extension Entomology Specialist and NMDA Entomologist, agreed that while both the adults and larvae may be making those holes, it won’t cause serious crop (or garden) damage. Dr. Sutherland added, “As far as I know, the tortoise beetles are long-time (but possibly part-time) residents of New Mexico. In the scientific literature, they were documented in the U.S. in the 1860s; otherwise, they’re supposed to be rather widely distributed in Central America and with ‘northward movement in spring.’ I’m asked about them every blue moon.”
That night, donning a headlamp and armed with a plastic cup of soapy water, I scanned my tomatillo and adjacent tomatoes for tortoise beetles, mostly nymphs.
Important side story: Last year, I saw a post about tomato hornworms being easier to find at night with a blacklight. Some arthropods fluoresce, or glow, under ultraviolet light (like from an electric blacklight). So I bought a $7 UV flashlight from a discount hardware store. It turns out not to be true for tomato hornworms—or not completely true. They are easier to find at night with a blacklight, but it’s not that they actually glow as much as their stripes reflect light, and it catches the eye.
Searching for tortoise beetle larvae that night, I wondered if they might be fluorescent too, so I got out my handy blacklight flashlight, and “OH, WOW! How cool!” To see the video of these glowing pests, more interesting details from Drs. Skidmore and Sutherland, and photos of other wild tortoise beetles from around the world, visit the Desert Blooms blog version of my column.
Warning! UV light can damage exposed skin and eyes. As an undergrad lab assistant at UNM, I forgot to wear the protective welding mask one time when using a tabletop UV lamp. Seven hours later, I was in the emergency room with my eyes swollen shut and punctate erosion of my corneas. I was told that if the exposure had been longer, I could have permanently impaired my eyesight. After three days of meds and keeping my eyes closed all the time, my corneas healed, but the skin around my eyes peeled, like after a bad sunburn.
Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: email@example.com, office: 505-865-7340, ext. 113.
Please copy your County Extension Agent and indicate your county of residence when you submit your question!