May 16, 2024

Cicadas are emerging in their billions across Illinois and parts of the Southeastern United States, as two unusually large broods — XIII and XIX — are heading aboveground for the first time since 2007 and 2011, respectively.

Periodical cicadas emerge every 13 or 17 years. After spending their juvenile years developing underground, they emerge in sync to transform into adults, mate, and lay eggs. The distinctive buzzing drone of the cicada chorus is produced by large groups of males, each singing a mating song to attract females.

According to Doug Yanega, Senior Museum Scientist at the University of California, Riverside’s Entomology Research Museum, what’s unusual about this year’s dual emergence is that “the broods involved are both very large broods, and there are a few counties in Illinois where they will physically occur together.” It’s for this reason that Illinois has been called “ground zero” for the dual emergence.

Humans may experience the sudden emergence of billions of loud cicadas as any combination of fascinating, irritating, or even disgusting. But the question that interests us at Wild Animal Initiative is seldom (if ever) asked: How do cicadas experience emergences?

What do we know about insect welfare?

Wild Animal Initiative has funded studies of insect welfare due to the research area’s potential to improve the lives of a very large number of individuals. Wild insects outnumber all classes of vertebrate species by orders of magnitude, but they are neglected in welfare research — due to their lack of charisma, perhaps, but also because very little is known about whether insects are sentient. But there is emerging research in this area.

In a 2022 review of neural and behavioral evidence from 350 studies, Matilda Gibbons et al. reviewed evidence of the capacity to feel pain in six orders of insects: Blattodea (cockroaches and termites), Coleoptera (beetles), Diptera (flies and mosquitos), Hymenoptera (bees, wasps, sawflies, and ants), Lepidoptera (moths and butterflies), and Orthoptera (grasshoppers and crickets). The review suggested that pain — and thus sentience — was plausible in several orders at the adult life stage, and a surprising amount of evidence was even found for some juvenile insects. The review marks a turning point in insect welfare research, since prior reviews had suggested that insects likely could not feel pain. However, Hemiptera, the order to which cicadas belong, was not included in the review because so few studies of the sentience-relevant neurobiology or behaviors of species within the order were available.

Meghan Barrett, Director of the Insect Welfare Research Society and an Assistant Professor of Biology at Indiana University Indianapolis, co-authored the review. She says that “there was a lot more evidence than I had expected there to be across the insects for proxies related to the potential capacity for pain.” She believes that the evidence we have so far “has suggested that it’s plausible, though far from definitive, that certain life stages in certain orders could have the capacity for welfare.”

There are millions of insect species, and the potential for sentience in hemipterans like cicadas requires much more study. However, given the growing evidence of sentience in other orders, it is both prudent and possible for researchers to begin thinking about cicada welfare. Barrett says, “there is enough accumulated evidence that, given our uncertainty about how sentience manifests, we should be cautious in our treatment of understudied insects until we have more and better information.”

Exploring questions in cicada research

With so little data available, Barrett suggests that one potential avenue for generating hypotheses to inform future welfare research is to combine what we do know about a species — like their life history and behavior — with the kinds of experiences that welfare researchers study in vertebrate species. For instance, we know that for vertebrate animals, experiences like being eaten by predators, resource competition, and disease are often negatively valenced. Barrett suggests these as starting points for insects like cicadas, too: “Most animals are not doing so hot when they’re getting eaten alive by other animals, so that may be true for insects, too.”

Barrett suggests resource competition, population density, inappropriate environmental conditions, predation, and disease could all potentially have negative impacts on cicadas’ welfare. Since Barrett specializes in bees and ants — which she notes differ significantly in behavior, life history, neurobiology, and physiology from cicadas — we asked Yanega to weigh in on cicadas’ possible experiences across these domains.

Yanega thinks it’s unlikely that nutritional availability is an issue for cicadas. Periodical cicadas feed on the fluids contained in tree roots, which Yanega describes as “effectively infinite.” When it comes to their environment, he says that periodical cicadas are likewise relatively hardy, seeming unaffected by unusually low or high temperatures.

Cicadas’ health is more difficult to form conclusions about, but causes of mortality point to potential areas of concern. According to Yanega, “most adult cicadas naturally expire,” but “a lot are eaten by predators.” On top of this, about 5% of cicadas are infected by Massospora cicadina, a pathogenic fungus that erodes cicadas’ abdomens. This accounts for mortality in a small number of 13- and 17-year periodical cicadas, which Massospora exclusively affects.

Adult cicadas are much more likely to die from predation than juveniles are. Indeed, cicada emergences are seen as a predator satiation strategy: The insects’ only defense from predators is the sheer quantity in which they emerge. Their numbers overwhelm predators’ capacity to consume them, so most survive — but many die.

Because juvenile cicadas (known as “nymphs”) live underground, Yanega says that they “are probably almost never eaten by predators.” This is a potential indicator that periodical cicadas could have better welfare expectancy than many other insect species. Periodical cicadas spend 99.5% of their unusually long lives underground, enjoying an abundance of food and a relative lack of predators. It’s likely that predation becomes a serious threat only in the final few weeks of their lives, when they emerge and become adults.

There is some level of uncertainty about this, however. As Yanega says, “it’s difficult to know what goes on underground.” More research is needed on what nymphs experience underground, and on other aspects of cicadas’ lives — including whether cicadas are sentient, and therefore have the capacity to “experience” at all.

When asked whether there are any questions about periodical cicadas that he’d especially like to see researchers answer, Yanega responds with a resounding “heck yes.” He adds, “we have no idea what the mechanism is that lets them ‘count’ years with so little error. There are always a tiny number of ‘temporal stragglers’ in each brood that come out one year too early or too late. What's different about those individuals, and how do the ones that come out the right year ‘know’ that it's the right year?”

Insects like fruit flies, scarab beetles, and cockroaches have been studied from a cognitive behavioral lens, displaying the capacity to learn (Greenspan and van Swinderen 2004; Farris 2008). Similar investigations into how cicadas keep track of time could be a step forward in welfare research. If emergences are a reaction to host trees’ seasonal cycles, as past research has suggested (see Karban et al. 2002), determining whether this is an instinctive or conscious response could provide some initial evidence about the possibility of sentience in the species.

If insect welfare is a field characterized by its nascency, cicada welfare is a particularly uncertain area, and this makes it difficult to know how we can help cicadas when we encounter them. At this stage, the most promising course of action may be to support further research that investigates these kinds of questions.