When a female emerges from her underground cell, she leaves her entrance hole with a characteristic behavior, in which she flies slowly in a straight line toward nearby trees. Mated females fly more quickly, zigzagging or abruptly changing flight, thereby distinguishing themselves from virgins. Males seeing a virgin in flight chase her, attempting to land on her back and fly off together to a resting place where he probes her genital region until locking with her. At this point, he releases his grip and falls backward, often dangling below her and appearing paralyzed or almost dead. Mating lasts on average an hour or so,7 with the record set in Ruby, Arizona, by a pair I watched for 2 hours 16 minutes. If the pair is disturbed, say, by a potential threat or another male, they fly off in a horizontal tandem with the female pulling and the male providing lift for his own body weight. This idealized scenario for male and female is rarely the case in crowded nesting areas with many enthusiastic males present. Frequently, a mob of several to many males grab onto the female, each male attempting to clasp her, and the ball falls to the ground as a seething mass. Eventually, one male succeeds in engaging her genitalia. He then has the task of pulling her from the mass of other clinging males. In rare, extreme cases as observed by Chuck Holliday, the female or males within the mating scrum might actually die from overheating.
Males with their “live fast, die young” approach to life sometimes are the losers because of their lifestyles. Males live on average 11 to 15 days. Female emergence occurs over a period of 23 to 49 days. Thus, to achieve maximum opportunities to mate, a male is most successful if his short life occurs over the peak emergence period for females. But peak emergence period varies widely from year to year. Some years female peak emergence occurs two to three weeks before or after other years. If a male “guesses” wrong in his emergence time, he might lose, irrespective of his large size. However, a small male might do well if he emerges at the best time.8 Little wonder a male cicada killer’s life is chaotic.
Predators, parasites, and diseases plague cicada killers. Their enormous size, loud buzzing, and bright-yellow and milk chocolate to rufous brown colors make cicada killers conspicuous to predators. Sometimes, this bright warning coloration works well; sometimes, it might not. Western kingbirds in Ruby, Arizona, have specialized in preying on cicada killers. Actually, they prey on the food for the next generation of cicada killers. A kingbird will chase and attack a burdened female returning to her nest with a cicada, forcing her to drop the cicada, which the kingbird grabs and eats. Kingbirds do not attack unburdened cicada killers.
Risks are also present at the cicada killer nest burrow. A variety of flies lurk around the nest entrances hoping to quickly larvaposit (many flies lay tiny live maggots instead of eggs on their targets) on the incoming cicada. If successful, the maggots quickly overcome the rightful owner’s egg and devour its cicada(s). More appealing parasites, at least to people, are the colorful velvet ants. These large velvet ants, sometimes called cow killers, sport beautiful fur coats with patterns of red and black, orange or yellow and black, or yellow or white. The velvet ants associated with cicada killers are among the world’s largest velvet ants, largely because their young have enormous nutrition available in the form of the larva of cicada killers. Once again, you are a reflection of what you eat.
The last, but not necessarily least, of a cicada killer’s risks is another cicada killer. Cicada killers leave their nest entrance burrows open, even when a cicada is present in a cell. Other females can exploit this opportunity to take over the cicada or even the entire burrow from the absent female. Such a takeover by a usurping intruder, if successful, is far easier than digging a new burrow and catching cicadas. Through a clever series of experiments using trap nests, Chuck Holliday and his associates showed that this apparent “kleptoparasitism” can reach more than 50 percent in experimentally abandoned nests.9
What about the sting? Surely, in a wasp this large with a 7-mm stinger, the sting must be of use in defense. Yet, few, if any, reports of attempted predation on adults, much less successful predations, are reported, which suggests that the sting is not needed. Perhaps simply the wasp’s appearance as a supersized yellowjacket, a beast to be feared and avoided, is all that is needed. The fact that few people seem to be stung by cicada killers could also suggest that the defensive value of their sting is minor, so minor that a person must exhibit real talent to be stung by a cicada killer. In many years of studying cicada killer wasps and their venom, I was never stung. During this time, wherever I went and mentioned cicada killers, people expressed great fear or apprehension of cicada killers. I was always asked how much does their sting hurt. My answer: “I’ve never been stung, but I expect it would not be too painful” somehow seemed unsatisfying to both the asker and to myself. I was the expert. So why such an unsatisfactory answer? Eventually, this got to me, and I had to do something. What to do? Ah, ask Joe Coelho, the expert mentioned earlier! Joe answered, “Oh, it is pretty trivial, sort of like a pin prick, not much pain.” My theory that it wouldn’t hurt much was supported. But still, maybe Joe was just underplaying it. Next, I looked in the literature and found one report from 1943. Charles Dambach was stung by a “large specimen” near the tip of his right index finger and wrote, “An initial sharp pain was followed by numbness, a slight swelling and stiffness which lasted about a week.”2 Again, this supported the theory that cicada killer stings wouldn’t hurt that much (note, no superlatives in his quote). Finally, I realized that I had to get the real story myself. In the popular media and in academic circles, the modern legend has it that “Schmidt is the guy who likes to sting himself with any imaginable stinging insect.” Cicada killer wasps are a main source for this legend. Yes, I needed to get the data on the pain level of a cicada killer sting. No, I hadn’t been stung in the heat of the battle. And, no, I did not want to sting myself. What to do? One day opportunity struck; a western cicada killer (Joe was stung by an eastern cicada killer) happened to be sipping nectar from a flower, and I was missing my net. I grabbed the wasp and wham, or perhaps I should say “slap,” I got stung. It wasn’t like getting hit by a bullet or a flaming torch; rather, it was like being stuck in the palm by a thumbtack. The pain was sharp and immediate, lacked any burning sensation, and lingered for about 5 minutes. There was no swelling, and the pain was entirely gone in 20 minutes. Pain level 1.5 on the pain scale, a lot less than a honey bee sting: a low level of pain for such a large wasp with such a huge stinger. Theory confirmed in person.
If cicada killers don’t attack us, and don’t sting us, and their stings don’t really even hurt much, why then have they become so imbued in human popular media? I ask for forgiveness from the medical and pest control industries here, for I associate them with popular media. When a local medical treatment for insect stings is to be marketed, does the industry feature one of the true culprits, a honey bee or yellowjacket wasp? No, they often feature an enormous picture of a cicada killer, flying from blackness right at you. When the pest control industry, the guys in clean, starched white outfits, who come to your house to spray or treat cockroaches or termites, need to display an insect for their magazine feature on stinging insects, do they feature a honey bee or yellowjacket? No, they feature a huge picture of a cicada killer, again with a black background. Why do professionals who know, or should know, that cicada killers are harmless, prominently feature cicada killers to represent stinging insects? The short answer is human psychology. Bigger is scarier. By simply mimicking the smaller, dangerous stinging yellowjacket wasp, the cicada killer becomes in our mind a “huge yellowjacket,” thereby winning the war of wits with humans—without ever having to show its sting. This same mimicry of stinging yellowjackets also appears to work on other large animals. Having nasty little fellows around that look like you has its benefits.
MUD DAUBER, THE WORLD’S MOST FAMILIAR SOLITARY WASP, adorns our structures with her graceful nest of mud placed on walls, under roofs, and, in bygone days, inside our outhouses. The mud dauber, Sceliphron caementa
rium, is also sometimes called the “dirt dauber,” or, if one wishes to be formal, the “black and yellow mud dauber.” She is the only wasp I know to have a book dedicated to her, and not just dedicated to the species but to a single individual known as Crumple Wing. Arnold Menke, a distinguished wasp expert from the Smithsonian Institution, also succumbed to the spell of mud dauber wasps. Arnold, coauthor of Sphecid Wasps of the World, a 600-page bible of sphecid wasps commonly called the Big Blue Book, adopted the pen name of “Mud D’aub” for many of his popular writings on wasps. I suspect Mud D’aub will not become as familiar a writer as Mark Twain, another pen-named author, but they both share the distinction of choosing their names based on their work and love: in Menke’s case, the familiar and beloved mud dauber wasp; in Clemens’s case, the riverboat terminology “mark twain,” for two fathoms of water depth, an indication of safe navigating water in the Mississippi River.
For all their familiarity to humanity, mud daubers seem cloaked in superstition and misinformation. Many people, especially in the southern regions of the United States, fear these wasps, especially their stings. Lynne Bachleda in her book on dangerous wildlife, wrote “mud daubers can sting painfully” and “the mud dauber’s sting is potentially lethal to those highly allergic and prone to anaphylactic shock.”1 Rod O’Connor writes, “[the mud dauber sting produces an] unusually mild immediate reaction on humans, i.e. negligible pain and swelling,” followed by, “but an authenticated case of mud-dauber sting death has since been discovered.”2 The “authenticated case” turns out to be an unpublished private communication, a perfect source for starting (or continuing) an urban legend. Not to be left out in the vilification of mud dauber wasps, Dr. Claude Frazier, a famous physician from North Carolina, showed in his review of allergic reactions to insect stings a photograph of a mud dauber along with the usual suspects: honey bees, yellowjackets, baldfaced hornets, paper wasps, and bumble bees. He also featured a cicada killer and a velvet ant. In fairness to Dr. Frazier, he never claimed any of these solitary wasps actually caused allergic reactions, but their guilt is implied by association.3 The record reveals not one allergic death documented from the sting of a mud dauber; indeed, even getting stung once, much less twice or more as needed for an allergic reaction, requires an exceptional talent.
More favorable views of the familiar mud dauber wasp trace to the famous early American naturalist John Bartram, who penned in 1745 the first observation of paralysis instead of death in a stung prey of a solitary wasp. He recorded this observation with the mud dauber: “Only in some manner disable the spiders, but do not kill them … that they may be preserved alive and fresh until the egg hatches, which is soon.”4 Bartram also noted that during their “Labours, they make a very particular musical Noise, the sound of which may be heard at ten yards distance.” Bartram’s first recorded observations are as correct today as during his time.
Perhaps the most unabashed fan of mud daubers was George Shafer, a professor of physiology at Stanford University. George investigated the basic physiology of digestion, plus the life history and biology of mud daubers. His affection for the wasps was obvious in his writings, with the invitation “To the prospective reader, I wish to commend this royal, thread-waisted wasp, Sceliphron caementarium, possessed of such grace and seeming personality as to invite acquaintance.”5 His writing entertained and inspired many young naturalists, including me.
The scientific lore of mud daubers is as rich and diverse as its folklore. Mud daubers become musical masons as they work the mud from which they build their nests. The “musical noise,” to quote Bartram, is generated by contracting the wasp’s thoracic flight muscles, thereby vibrating the head and mandibles while emitting a high-pitched sound. When digging mud from the source and then plastering it on the nest, the wasp uses sounds of different frequencies, apparently optimizing the digging, plastering, and smoothing processes.6 The finished mud nest sometimes then becomes a preferred attachment site for barn swallows, birds that also fashion their nests from mud.7 Mud dauber nests sometimes even become the targets of downy woodpeckers, which chisel holes in the nests and extract a meal of cell contents.8
Mud daubers are not simply fine masons (their scientific species name caementarium is derived from Latin for “mason”), they are chemists as well. Within mandibular glands in their heads mud daubers produce geranyl acetate, a compound with a pleasant floral or fruity rose aroma to the human nose, and 2-decen-1-ol, which has a fatty odor.9 The purpose of these odors in unknown, but likely they serve as chemical warnings or defenses directed toward predators. Other mud dauber talents include flower pollination, in which they rate the 10th-most important pollinator of carrots in Utah.10 They are about average among insects in their ability to survive gamma radiation produced by cobalt-60. The American cockroach, the big juicy cockroach that emerges from sewer drains and is loathed by homeowners, was also part of the study. Perhaps surprisingly, the cockroach was the most susceptible to radiation of all tested insects,11 which refutes the legend that after a nuclear war the only survivors would be cockroaches.
A final superlative talent of mud dauber wasps is their ability to invade and colonize new lands. No other solitary wasp can match their dispersal ability. Its closest competition among bees might be the honey bee, but its dispersal was almost entirely with the help of humankind who intentionally brought them to all peopled major landmasses. Mud daubers are not intentionally spread by humans; nevertheless, they have spread, among other places, to Europe, Japan, and even the Galápagos Islands made famous by Charles Darwin. Their dispersal seems to be as mud nests attached to shipping boxes and incidentally transported in commerce. Once in a new location, mud daubers appear to have good success in colonizing. Curiously, the first reported records of mud daubers in France and Japan were in 1945, about the time World War II ended and reconstruction in Europe and Japan began with American materials shipped from North America, the native home of mud daubers.
What makes mud daubers so omnipresent and successful? Part of the answer is their natural history. Mud daubers build their nest of mud and provision them with spiders for their young. Both mud and spiders are universal components of most habitats. Mud daubers are only semi-fussy about their spider prey. Their favorites are orb weaver spiders, followed by crab spiders and jumping spiders.12 Mud daubers locate spiders visually and pounce on them. Spiders are recognized by cuticular components on their exoskeleton. If the attacked object is not a spider, the wasp discontinues the attack and continues searching. Recognition cues are distinctive not only to spiders but also to specific types of spiders. In a study, Divya Uma extracted the waxy components from the integuments of several types of spiders and applied them to paper dummies. Mud daubers attacked the dummies coated with extracts of spiders that made two-dimensional webs (familiar orb weavers found in gardens) but avoided dummies with extracts of spiders that make three-dimensional webs, in this case the common gray house spider, a cobweb spider that makes a tangled web. The wasps stung the two-dimensional web makers or dummies coated with their extracts but rarely attempted to sting the three-dimensional web makers or dummies coated with their extracts.13 One species of jumping spider, a normally accepted group, evolutionarily “out-foxed” the mud dauber by having a different chemical coat that was not recognized as “spider” by the wasp. The disguise was even better—the spider looked like a carpenter ant.14
When the mud dauber finds a suitable spider (a test best failed in this case if the spider is to survive), the wasp grabs it with its mandibles and front legs and stings the spider under the cephalothorax, the head-thorax unit. Three stings directed toward the nerve ganglia that control jaw and leg movement are the usual pattern. The stung spider immediately becomes limp and paralyzed. The mud dauber will often press its mouth to the spider’s mouth and drink from it. Sometimes, the wasp will also chew through the spider’s leg base or abdomen and drink fluids. Why the wasp does this is unclear. By drinking the spider’s fluids, the mud dauber deprives i
ts young of a high-quality spider, and sometimes the spider entirely, as the spider may be discarded after the drink. Perhaps the reason for drinking from the spider is to obtain valuable protein, a nutrient woefully lacking in the mud dauber’s usual diet of sweet nectar. When not used solely for personal benefit for the wasp, the spider is transported to the mud nest and pushed into a premade mud cell. An egg is laid on the first spider and the wasp goes in search of more spiders. When 6–15 spiders have been added, the cell is capped with mud and a new cell started, attached to the growing mud blob. A dozen or so cells are constructed, filled with spiders, and sealed in this fashion during the female’s six-week to three-month life span. The egg in the cell hatches into a tiny, nearly transparent larva, which sets about feeding on the provided spiders. When all spiders are consumed, the fattened larva spins a silk cocoon, rests several days while the connection between the gut and rectum forms, and then defecates in the bottom of the cell. The larva, now called a prepupa, an intermediate stage between the true growing larva and the pupa, rests quietly overwinter in its silken enclave. At the end of winter, the prepupa molts into the pupa, which then metamorphoses into the adult. Adults rest in their cells several days while hardening their cuticle and then chew through the hard mud cap to emerge. Males, like males of most sphecid wasps, are smaller than the females and emerge shortly after the first females in the early season. Though mating behavior in mud daubers has been a neglected topic, females apparently mate shortly after emergence and start their summer nest building and foraging behavior.
Mud daubers can and do sting spiders. Do they sting in defense? Perhaps, but it’s unclear at best. If a mud dauber is grabbed, it will curl its abdomen against the offender in a stinging motion, an action males, which have no stinger, and females perform equally. When this happens, the reaction of most people, entomologists included, is to release the wasp immediately. Thus, no sting is received and the wasp wins. Is this all bluff, or is there real substance behind the action? I support the bluff concept because males are released as readily as females, and both males and females are mimicking honey bees and yellowjackets that do readily sting. Is it worth taking the risk that one’s identification is wrong? Evidence against meaningful pain subsequent to the “stinging” action is the infrequency of documented stings to humans. I personally know of nobody who has been stung. Negative evidence is, of course, only a teaser; I fully accept the idea that mud daubers are able to sting people, as illustrated by Rod O’Connor’s earlier statement of a sting that produces “negligible pain and swelling.”
The Sting of the Wild Page 18