BODY SIZE RANGE. Male cicada-killers show a large range in body size. The unfertilized eggs which develop into male cicada-killers are provisioned with only one cicada by their mothers. Thus, they get only half the food that their better-nourished sisters get and they are correspondingly smaller at maturity. The picture on the left is of three male wasps; the one on the left is the smallest one I have caught (198 milligrams), the middle one is above average in size and the one on the right is the largest one I have caught (947 mg).

One might well ask how such a large range in body size is possible if each male is issued only one cicada. Small males may have gotten a small male cicada (male cicadas weigh less than females in all three Tibicen sp.used as prey and the three cicada species are of different sizes as well) or their cicada may have begun to rot before they finished eating it. It is also possible that small males had to compete for food with fly larvae laid on their cicadas as they were being handled near the burrow mouth by the wasps' mothers. On the large end of the scale, big males may have gotten a really large female cicada (some weigh over 2000 mg). Another possibility is that they were intended to be females and were given two cicadas by their mothers, but the egg was not fertilized by the sperm she added from her spermatheca when the egg was laid. This possibility seems less likely, however. Fabre mentions experiments with French sphecids in which he gave male larvae a second prey insect and it was consistently refused. I have repeated this experiment once with a male cicada-killer larva in the laboratory and it, too, would not start eating the second cicada. On the other hand, biological processes are rarely more than 30% efficient at harvesting energy and this implies that a 947 mg male would require a 3157 mg cicada if it will only consume a single one, as suggested by my result and those of Fabre.

I have captured 50 female wasps returning to their burrows with cicadas and only two of the cicadas, both females, weighed over 2000 mg (2061 and 2109 mg), so I feel certain that 3000 mg cicadas are rare indeed. Thus, it apears likely that the 947 mg male in the picture above must have been issued two cicadas by its mother and eaten them both. Perhaps he suffered from a hormonal or genetic derangement and was a female genetically but a male phenotypically and, thus, was given and ate two cicadas after all.

The graph above on the right shows male and female body mass distributions in 50 mg increments. It is obvious that my 947 mg male is in a league by himself and this makes it possible that "he" was really a "she" with a genetic or developmental problem; however, he had 13 antennal segments (females have only 12). As can be seen in both sexes, there is a very large range in body mass. For 465 males: range = 198-947 mg, mean = 424 mg, median = 402 mg. For 422 females: range = 356-1564 mg, mean = 967 mg, median = 969 mg. I have experienced much difficulty in laboratory rearing of wasp larvae because of mold growing on the cicadas on which the larvae are feeding and I have several times found larvae in artificial burrows (see Larval Development section) apparently killed by mold or, perhaps, disease. Dambach and Good (1943) note that they have found fly larvae eating the cicadas in wasp nest chambers and this would have reduced the amount of food available to the wasp larvae. Perhaps the annual variations in wasp size reflect differences in fly populations and reduced food availability to the wasp larvae as well as variations in the size of cicadas available to hunting cicada-killers and in the degree of fouling of the cicadas by mold, all of which would restrict food availability.

The graph on the left above shows male body mass distributions for four years (1990, 1991, 1997, 1999) in which I caught and weighed more than fifty male wasps. Male size distribution varies from year to year and the males in 1999 were significantly larger than in the other three years. Further, in 1999 the body mass distribution is bimodal, with two peaks, one centered on the 350-399 mg size range and one centered on the 500-549 mg size range. This annual variation in size may also reflect differences in fly populations and reduced food availability to the wasp larvae as well as variations in the size of cicadas available to hunting cicada-killers and in the degree of fouling of the cicadas by mold, all of which would restrict food availability.

COMPETITION FOR FEMALES. Given the very large range of body size in male cicada-killers, it would be expected that males might compete for access to virgin females and that such females might have some way to assess male fitness and mate only with those males which appear most fit. Before mating, males mount the female and shake her head back and forth with their front legs and tap the female's antennae with their own. This precopulatory behavior provides the female with ample opportunity to assess the male's weight (she's carrying him) and his strength (he's shaking her head; both activities are shown in the picture on the left). Joe Coelho and I have published a paper (J. Insect Behavior 14: 345-351) presenting data which show that, when several males are competing for the same female in the wild, the one which manages to mate with her has a significantly larger percentage of body mass as flight muscle (thorax mass, actually), perhaps indicating a higher degree of fitness in aerial fighting and a better ability to keep other males off of a given area of the lek when virgin females are emerging.

However, in situations where a single male is present on the lek, newly-hatched females may not be able to afford to be picky if they wish to mate. Given the vagaries of male and female hatching and male presence on the lek, there are probably many cases when there is only one male available to mate with females which have hatched and are ready to mate. I simulated this situation in the lab by offering the smallest male wasp I have captured (198 mg, "Tiny Tim") to three different virgin females at one-day intervals. Tiny Tim was readily accepted by all of the females and mounted and mated each one within the first minute of their time together in the container. So, at least in the laboratory and when only one male is available, "It's not the size of the wand that puts the rabbit in the hat, but the skill of the magician." Tiny Tim is shown hanging in there with a small female in the picture of the nuptual couple above on the right. There is much more information (including movies) on mating in cicada-killers on the mating page.

MALE PERCHING AND TERRITORIAL DEFENCE. It is possible to tag cicada-killers with numbered paper tags secured to their backs (thoracic dorsum) with alpha-cyanoacrylate glue (Krazy-Glue, thick formulation) under carbon dioxide anesthesia, as shown in the picture on the left. Using such tags on 169 males (69 of which were seen again at least once after tagging) on seven active leks, I have been able to show that in nearly all cases (61 of 69 marked wasps) males remained at the lek where I first found them. Only eight males were found at leks other than the one of original capture and five of these were visiting a lek only 20 meters away; the other three males were seen at leks 50-100 meters from the lek where they were marked.

A crowded lek with ten or more lek males defending territories and satellite males swooping by to patrol for emerging females as long as they can before being chased off by the lek males is a very busy place. Lek males defend territories on the lek and will use local topographic features as boundaries and, probably, reduce wasted effort in fighting males with neighboring territories. Trinca and Eason (1994) have published an abstract of an interesting study in which yard-long dowels were placed so as to redefine the boundaries of the territories of the lek males. They found that the lek males adopted the dowels as the boundaries of new territories (their own and their neighbors') and thus reduced their antagonistic interactions. Here's a 224 KB Quicktime movie of a male leaving his perch to chase aother male.

When males interact with other cicada-killers it appears that they are attempting to mount the other wasp's back, as in the preliminaries to mating. Of course, another male or an already-mated female will actively resist such and attempt and this results in much flying in tight circles around each other and grappling in the air and the pair may face off and rise vertically up to five meters in the air, each one grappling with its legs to mount the other wasp's back. Such pairs of fighting wasps may fall to the ground and continue to grapple. Lek males often knock down females which are flying slowly over the lek looking for an active burrow or a good place to dig one. Thus, it seems that male cicada-killers try to mount anything of the right size that is moving and which doesn't fight back vigorously, as in the picture on the right [This picture of a female and three males brings to mind the old Abbot and Costello comic routine, "Who's on first?" In this picture it's easy to answer the question.] The two males trying to mate with an already-mating female on the right are not showing strange behavior; I have seen such "scrums" in the wild as well. Lin (1966) noted that mating pairs often fly off of the lek with the larger and stronger female leading and the male being towed behind (the male tries to fly the other way but is dragged backwards by the female). The pair alights nearby in vegetation or on the ground and remains quietly in copulo for an hour or more before separating. Males can lock themselves into the female during copulation and this lengthy period of copulation is probably a form of mate-guarding by the male to keep rivals from adding their sperm to the female's spermatheca.

MALE POPULATION SIZES ON EASTON LEKS. Using males marked with paper tags as described above, I have also been able to do mark-recapture experiments to determine the size of male populations on several leks in Easton by marking 10-30 males from each lek, letting them mix with the other males on their lek and then sampling the whole male population to determine the percentage of marked males present. The "dilution" of the marked males by the unmarked males in the population allowed me to calculate the size of the resident male population, including both leking and satellite males. The graph on the right shows the male sightings on a typical lek in Easton at Lafayette's Van Wickle Hall in 1990, on which mark-recapture measurements made by capturing all males (marked and unmarked) on the lek showed a male population size of 103 on a grassy area 3 meters by 10 meters with satellite males using bushes and trees up to 30 meters away. Lek males were often found on the same perches several days in a row and several of them changed perches and then occupied the second perch for several days before disappearing from the lek, probably due to mortality. It is not uncommon to find dead males on or near an active lek.

The graph on the left also shows that many of the males (43%) were not seen again after they were captured, marked and released again on the lek; perhaps they were satellite males and, thus, less likely to be caught, or perhaps they were caught and marked just before they died. Fifty-seven percent of the marked males were seen at least once after marking and the longest stay on the lek was 15 days; this time probably represents the upper limit of a male's life above ground. I have kept cocoons over the winter in my lab by slowly cooling them to five degrees C and slowly warming them to room temperature in the following spring. Two males hatched from four cocoons so treated; they spent 169 and 181 days in their cocoons and, after emerging, they lived on apple juice and water in my lab for 31 and 12 days, respectively. Lin (1978) gives the maximum longevity of male cicada-killers as "about 15 days" and for females the number is "30-33 days."

MALES ARE FAMILIAR WITH A LARGE AREA AROUND THEIR HOME LEKS. Male wasps are able to return to their home leks when marked and moved over 2 kilometers away. Two experiments done in 1997 gave the following results: a) eleven of twelve males released 0.9 km away returned to their home lek after 1-2 days and b) eight of ten males released 2.3 km away returned to their home lek after 2 hours to five days; none of these 22 males were sighted at any of the seven leks under observation other than their home lek. Thus, males probably search for food over a large area around their leks and are quite familiar with their local geography. In this regard, although I have spent well over 1000 hours in field observations of cicada-killers over a ten-year period, I have never seen them feeding. Males often disappear from their leks in the heat of the day (11 am through the early afternoon) and return in small numbers later in the day (after 4 pm); I presume they are feeding during these times. Lin (1967) notes that males are present on the leks only during the morning hours and often do not return in any numbers until the next morning. Dambach and Good (1943) report that cicada-killers have been seen feeding on "...exudations of various trees, including willows, oaks, sycamores, and the flowers of compositae and other plants." A few readers of this page have e-mailed me similar observations.