Cicadas and Cicada Killers

For some reason, the call of a cicada makes a summer day feel even hotter! What call? Well, whether you realize it or not, you know the sound to which I am referring. It starts like a revving engine and continues as a sustained shrill or buzzing noise. Produced by the vibration of membranes in the insect abdomen over a resonance chamber, sound is made by a drum-like structure and is used by males to attract mates. In morning, afternoon or evening, you can’t miss the sound of a drumming cicada!

Cicadas are much more than the soundtrack of a hot summer. They have a unique life history that is obscure and difficult to study, since development of nymphs occurs entirely underground! It all starts when an adult female cicada lays eggs in the twigs of a tree or shrub. This typically kills the growing twig, and provides an ideal incubation site for eggs. After about a month, eggs hatch and newly emerged nymphs drop to the ground where they will feed on the roots of perennial plants.

That is exactly the point when things get interesting biologically. You see, there are two major groups of cicadas differentiated by the time it takes for nymphs to develop. The first group is the dog-day cicada, making references to the time of year when adults emerge in July and August - the “dog days of summer.” These are large, green and black insects that have clear wings and make a rattling sound during flight. Nymphs of dog-day cicadas may take 2-3 years to develop, but because they exhibit overlapping generations with adults emerging every year, they are present each summer to fill their air with the mating songs. On tree trunks and other vertical surfaces, you can find the exoskeleton of the last nymphal instar: a tan shell of an insect with claws and rather large eyes. In the middle of the back is an opening from which the adult cicada crawled out, expanded its wings and flew off.

Whereas the dog-day cicada is present every year, periodical cicadas exhibit mass emergence on a cycle of every 13 or 17 years! That’s right; these black and orange insects with red eyes remain in the soil for over a decade, slowly feeding on plant roots and all emerging in May or early June of the same year. Why such a long development time and mass emergence? This life cycle is thought to provide protection from predators by making periodical cicadas an unpredictable food resource. During a mass emergence predators are overwhelmed by the abundance of cicadas, and are not capable of depleting insect numbers. This guarantees the success of the species by providing ample mating opportunities for the cicadas.

There is a predator out there that gets the phones buzzing at pest management companies around this time: the cicada killer. This insect is a solitary wasp that captures cicadas and uses them to nourish their offspring. Cicada killers are some of the largest wasp species in North America and hunt by sight. Textbook descriptions suggest that these predators capture prey in flight, something I did not believe until I saw it firsthand. As a graduate student I conducted field research on an agricultural farm in Delaware, which exhibited bare, sandy soils common of the coastal plain. Ideal habitat for cicada killers that burrow up to four feet into the ground, my plots were peppered with burrows made by the female wasps. I watched as aggressive, but stingless males flew around female burrows to either guard their mate or to find mating opportunities. It was one sunny afternoon that a cicada carelessly flew from one hedgerow to another across the field, when suddenly a cicada killer swooped in to grab/sting the insect and bring it to the ground. Paralyzed by the venom, the female would then bring the cicada back to its burrow as a feast for her offspring. The insect world is a cruel place!

What can you do to prevent these large wasps from taking up residence in your yard? Cicada killers are attracted to bare spots of open soil. Spring or fall plantings of grass or a creeping groundcover can be used to fill bare spots, making these sites inhospitable for cicada killers to burrow. Keep an ear out for cicadas this summer - you're sure to hear them!