Summary: In May, 2024, brood XIII appeared as predicted in central Missouri. I discuss the facts I discovered during my background research and my own observations.
Background
Life cycle
The nymphs of the periodical cicadas live underground, usually within 2 ft (61 cm) of the surface, feeding on the juices of plant roots. The nymphs of the periodical cicada undergo five instar stages in their development underground. The difference in the 13- and 17-year life cycle is said to be the time needed for the second instar to mature. When underground the nymphs move deeper below ground, detecting and then feeding on larger roots as they mature.1
Emergence
The nymphs first emerge on a spring evening when the soil temperature at around 20 cm (8 in) of depth is above 17.9 °C (64 °F). The crepuscular emergence is thought to be related to the fact that maximum soil temperatures lag behind maximum insolation by several hours, conveniently providing some protection for the flightless nymphs against diurnal sight predators such as birds. For the rest of their lives the mature periodical cicadas will be strongly diurnal, with song often nearly ceasing at night.2
Reproduction
After mating, the female cuts V-shaped slits in the bark of young twigs and lays about 20 eggs in each, for a total clutch of 600 or more. After about 6–10 weeks, the eggs hatch and the nymphs drop to the ground, where they burrow and begin another 13- or 17-year cycle.3
Broods
n 1907, entomologist Charles Lester Marlatt assigned Roman numerals to 30 different broods of periodical cicadas: 17 distinct broods with a 17-year life cycle, to which he assigned brood numbers I through XVII (with emerging years 1893 through 1909); plus 13 broods with a 13-year cycle, to which he assigned brood numbers XVIII through XXX (1893 through 1905). Marlatt noted that the 17-year broods are generally more northerly than are the 13-year broods.
Many of these hypothetical 30 broods have not been observed. Marlatt noted that some cicada populations (especially Brood XI in the valley of the Connecticut River in Massachusetts and Connecticut) were disappearing, a fact that he attributed to the reduction in forests and the introduction and proliferation of insect-eating “English sparrows” (House sparrows, Passer domesticus) that had followed the European settlement of North America. Two of the broods that Marlatt named (Broods XI and XXI) have become extinct. His numbering scheme has been retained for convenience (and because it clearly separates 13- and 17-year life cycles), although only 15 broods are known to survive.3
Only four broods of periodical cicadas extend into parts of Missouri: two of the 13-year type and two of the 17-year type.5
Pathogenic fungus
Massospora cicadina is a pathogenic fungus that infects only 13 and 17 year periodical cicadas. Infection results in a “plug” of spores that replaces the end of the cicada’s abdomen while it is still alive, leading to infertility, disease transmission, and eventual death of the cicada.5
Mites
In 2007 and 2008, Edmond Zaborski, a research scientist with the Illinois Natural History Survey, reported that the oak leaf gall mite (“itch mite”) (Pyemotes herfsi) is an ectoparasite of periodical cicada eggs. While investigating with the help of others the mysterious itchy welts and rashes that people were developing in Chicago’s suburbs after the end of a 2007 Brood XIII emergence, he attributed the event to bites by mites whose populations had quickly increased while parasitizing those eggs. A similar event occurred in the Washington, D.C., area after a Brood X emergence ended in 2021.6
Media disinformation
- There were lots of posts on social media about there being a lot more copperheads around eating cicadas. While it is an interesting fact that copperheads eat cicadas, there is no reason to think that copperheads become more common during the cicada emergence. I have lived through multiple cicada emergences in the past and have never seen an excess of copperheads.
- The news media made a big deal of the emergence of two broods at the same time. These two particular broods have not emerged together since 1803. However, they do not geographically overlap so no area is inundated with more cicadas than normal. And double emergences are not uncommon given the number of broods.
Vocabulary
- instar: A developmental stage between two molts in the life cycle of an arthropod, such as an insect or crustacean. For example, the larval stages of insects often go through multiple instars before reaching maturity.
- teneral: Referring to an arthropod, especially an insect, that has recently molted and is soft-bodied, pale, and not yet fully hardened or pigmented. This stage is vulnerable as the exoskeleton has not yet solidified.
- ecdysis: The process of molting or shedding the outer exoskeleton in arthropods and other invertebrates, allowing for growth or metamorphosis. It is a critical part of their life cycle.
- exuviae: The remains of an exoskeleton or outer covering that an arthropod or other organism sheds during molting. The exuviae often retain the shape of the organism and can be used for identification.
My observations
- Starting in early spring, I noticed a lot more mole holes in the yard than in previous years. Was this due to cicada nymphs beginning to emerge?
- First sighting: May 12, 2024. I noted 1 adult that had recently emerged and multiple (20+) exuviae. Also saw 3-4 holes in the ground. All of this was noted mostly around pear trees. I had not seen anything noticeable 2-3 days earlier.
- Crepuscular emergence: Over the next two days, I observed the trunk of a tree several times throughout the day, noting that there was little activity until around 7 pm, then multiple cicadas were seen crawling up the trunk.
- Speed: I estimate the speed of a crawling cicada nymph at about 8 inches a minute although I haven’t measured this accurately on more than one specimen.
CoMo Science 
Leave a comment