This is part of the 2020 Digital Seaside Center. For more Digital Seaside Center content, click here.

Hello everyone! Welcome back to local wildlife weekly.

I’ve written about insects now twice during this blog series, profiling a dragonfly (seaside dragonlet) and bees. These insects, while certainly not cuddly, at least escape most conventional disdain directed towards the class. Dragonflies keep their distance, and are a known check on much-hated mosquitoes; bees, while feared for their sting, are at least respected for their essential roles as pollinators. Most other insects are not as beneficial, and there is, unfortunately, often a price on their head.

In my post on bees I presented an overview of order Hymenoptera, which includes bees, ants, and wasps. Bees may be tolerated, but the rest of the order are usually classed as pests. Think of the aisles of any lawn-care store, and the endless bottles of poison directed at ants, wasps, and hornets… many people might be content to see these insects wiped from the face of the earth. While I will not pretend to enjoy spending time with, say, yellowjackets (shudder), I do recognize their right to existence, and find their natural history fascinating. In fact, wasps (suborder Apocrita, of which yellowjackets are a member) are some of the most remarkable insects around. They are incredibly diverse, overlooked, and, in some cases, simply beautiful! Additionally, wasps engage in many unique behaviors, and although we may find some to be disturbing and alien they speak to a rich evolutionary history. While I’m not saying we need welcome every wasp with open arms (we should sometimes keep a distance), our generalized hatred for them is misplaced.

One wasp that gets a particularly bad rap is the eastern cicada killer, one of our larger and scarier insects. Even its name is insidious, speaking to targeted murder and nothing more. While we have assigned these wasps to a villainous role, the reality of their niche is much more complex. Let’s explore why!

Introducing: The Eastern Cicada Killer

An eastern cicada killer at the Marshlands Conservancy in Rye, NY. Photo by Brendan Murtha.

The eastern cicada killer, Sphecius speciosus, is a formidable looking creature. Large, loud, and unmistakable, these wasps look as though their sting could knock a man dead. They have vacuous amber eyes that betray no evidence of empathy or compassion: there is, after all, a mindless cruelty in the face of a predatory wasp long recognized as unsettling. Cicada killers buzz low to the ground in a blur of bright scarlet, black, and yellow, and most people dance out of the way to avoid them as they pass.

Unlike wasps that build communal nests, cicada killers are solitary. Females dig burrows in soft soil, leaving mounds of excavated debris around the entrance (a bit like the groundhogs we looked at last week). Multiple females will occasionally share one burrow entrance, but the tunnel will split off into individualized cells where each wasp lays her eggs. Lawns are often chosen as a nest-site, especially along the edge of garden beds, and this brings the insects into conflict with humans. Fortunately, unlike communal wasps, cicada killers will not sting to drive off intruders. They are thus much less of a threat to people than their appearance suggests: cicada killers are reluctant to sting even when held between two fingers! When they do occur, stings are described as feeling like “little more than a pinprick,” and male cicada killers cannot sting at all. Our fear for them is thus largely irrational, and I hope we can one day reach a point where residual aversion is a result of mere squeamishness rather than deathly fear. That being said, I accept that emerging cicada killers will always solicit a scream or two– some primal biases just can’t be overcome.

I’m tempted to describe cicada killers as gentle giants, but doing so would invalidate the experience of cicadas. The wasps’ name, while over-simplified, does get at a hard truth: they are a cicadas’ greatest fear. Females are reluctant to sting humans because their toxins must be conserved; cicadas receive no such mercy. Cicada “killer” is almost too kind a title— this is no swift murder, but a prolonged and torturous end.

You might be surprised to learn that the adult wasps are actually vegetarian, sipping flower nectar like lazy bohemians. Their cicada-eating days are over; adult cicada killers take prey only for their young. The wasps paralyze cicadas with toxin from their stinger, and although the victims remain alive, they’re completely immobilized. The wasps will then carry the paralyzed cicadas back to their nest, weighed down by the limp body. It’s not uncommon to see this transport in progress, with the cicada killer struggling to stay airborne just above the grass. The cicada is often too heavy for the wasp to pick off the ground, so cicada killers must haul the cicada up a tree or post before taking off, dropping from a branch or associated perch. Once the cicada is in the burrow, the adult wasp will deposit it in a cell and lay a single egg atop its body. After sealing off the chamber, the adult leaves to repeat the process.

Now the real horror begins. The cicada, still alive, will lie still for a day or two until the egg hatches. The newly born grub, a larval wasp, will then begin to feed, slowly eating the cicada alive in its tomb. How long the cicada actually stays alive is unclear, but the wasp’s strategy is foolproof: the larvae come into the world with fresh meat on their table. As a result, the young can grow relatively quickly. Once the whole cicada is consumed the (now engorged) grub will pupate, spending the winter dormant before emerging as a winged adult in late spring. While their thirst for flesh has then been satisfied (nectar will now do) the adult wasps feel little remorse; they will immediately pass on cicada bodies to their progeny, and the cycle continues.

A cicada’s mortal enemy. Photo by Brendan Murtha.

Cicada killers nurture their young exclusively on cicadas, which are most common during the late summer months the adults are active. This is no coincidence. Many wasps engage in similar behavior, feeding their young the fresh bodies of other paralyzed insects, and are often specialized to terrorize a specific victim. This specialization dictates the wasps’ flight period, habitat, and morphology. We can see how cicada killers are barely large enough to handle their prey as it is; smaller wasps could not infringe on their food source. Such specialization reduces competition between wasp species and allows for rapid niche diversification: many avenues for adaptation open up from a single developed behavior. Wasps that engage in such behavior are colloquially called “hunting wasps,” and this group is paraphyletic. What this means is that “hunting wasps” do not all share a common ancestor; the strategy arose independently across many different wasp lineages. It could be called an example of convergent evolution, albeit on a smaller scale than we are used to (convergent evolution is commonly used to describe the development of flight across birds and bats, etc.).

The question then arises: where was the specialization introduced? Does a wasp lineage discover the strategy and then specialize, diversifying primarily from a common ancestor? Or has the behavior arisen already specialized, in response to a particularly abundant prey source, etc.? This is a type of question evolutionary biologists grapple with frequently: parsing out cause from effect can be quite difficult in the ever-unfolding narrative of evolutionary dialectics.

One important thing to note is that, while “hunting wasps” are paraphyletic, a precursor to the strategies’ development was the existence of a stinger. Wasps with stingers are monophyletic, meaning they comprise a clade: in wasps, all stingers can be traced back to a common ancestor. This “stinging” clade of wasps is called Aculeata. In this sense, the convergent evolution of “hunting” behavior is already the result of a specialization– and this sort of negation goes on with each rewind of the clock. What a labyrinth! This is one of the reasons evolution can be so furiously debated— it’s rarely cut and dry– but the ambiguity is, at least to me, what makes it so fascinating.

Often, when a predator is specialized to feed on one specific prey item, that prey item undergoes resultant adaptation to avoid being eaten. This then incentivizes further adaptation of the predator, to circumvent the prey’s defenses, and on and on it goes: such a “snowball” effect is commonly called an evolutionary arms race. Such races are responsible for some of the most incredible looks and behaviors in the animal kingdom. We rarely ever see cicadas: they possess excellent camouflage, and I wonder why? While the insects are also prized prey for some birds, I’d imagine cicadas would opt to go by kingbird rather than cicada killer if they had the choice. With the birds, at least, death comes quickly.

As I said at the beginning of the post, wasps are not mere villains— their culling of cicadas is important for the health of local ecosystems. Cicadas lay eggs under the bark of mature trees, often on dead or dying limbs where the bark is loose. However, when cicada numbers spike, healthy branches are also targeted for egg-laying, and the process can “flag” healthy limbs and kill them. Under extreme circumstances, young trees are colonized, and rampant egg-laying can doom them for good. Cicada killers keep cicadas at healthy levels, acting as an environmental check, and thus keep our forests healthy. Such balancing acts are not uncommon; predators are often directly responsible for the health of the environment in which they live. Furthermore, like many other “hunting wasps,” the nectar feeding adults can be important pollinators for certain plants. Wasps often join bees and butterflies in flower-patches to feast on the sweet, sugary bonanza and transport pollen from flower to flower as they do.

To make a long story short: although they may look nefarious, don’t kill the cicada killers! I am not asking you to keep them as pets, or even love them– please just tolerate the wasps, as you would tolerate bees. Here, “violence” on the part of the wasps should not beget violence towards them from us– those we deem villains are often just misunderstood, and any of our attempts to achieve “justice” for the cicadas will certainly backfire. Such is the way these things often go. The cicadas will ultimately be OK, and the entire ecosystem benefits from having the wasps around.

Hope you learned something here! See you next time!

-Brendan Murtha, 2020 Seaside Center Naturalist