Download Behavioral Analysis and Review of

Behavioral Analysis and Review of
Cannibalism in Praying Mantids
Timothy A. Bragg
Department of Biology, S.U.N.Y. Oswego, Oswego, NY 13126
Received May 13th, 2008
Abstract. – Cannibalism among praying mantids is not always the normal
occurrence even when considering the common misconceptions of male mantid
beheadings during copulation. Praying mantids are a very unique species of insect
with perculiar behavioral interactions. While cannibalism doesn’t occur with every
encounter between male and female mantids during copulation, it is still a very
important part of the population dynamics of mantis populations in field research.
Though some species are communal, a greater portion of the Order, and the 2,300
varrying species of mantids are in fact cannibalistic as a factor to limit competition
for food and promote individual fecundity of the brood survivors. Other important
factors contribute to fecudndity of future generations such as non-cannibalized
nutrition sources, timing of nymp emergence, oothecal sizes, and molting
synchronization; including quantity of specie’s instars.
Introduction. – Mantis religiosa (L.), from the order Mantodea, and the family Mantidae,
commonly referred to as the praying mantis, has an especially peculiar breeding behavior.
This species of insect is such a predatory species that it preys upon its own kind throughout
its life cycle. They eat other insects such as caterpillars, butterflies, flies, bees wasps and
moths by attacking them in a rapid striking motion (1/20th s) with their large, sharp, and
spiny front legs. Larger species of mantids will eat small lizards, hummingbirds, and frogs
(Patterson 1993). Even their own siblings can fall prey to one another shortly after coming
free from their egg casing which can contain upwards of 400 offspring. Their unique ability
to turn their head side allows for an even more deadly combo of stealth and agility
(McCommons 2001). It is considered common for the female to devour the male after
copulation has taken place, and it is slightly more likely during copulation; with removal of
the head actually stimulating the male’s body to deliver sperm more rapidly. Besides
making sperm delivery more efficient, a possible reason for this behavior is that the male is
simply the nearest high protein source food for an expecting mother. Similar to other
insects, female mantids are capable of releasing sex pheromones at night which generally
attracts more than one male. Males then may proceed to perform a sort of courtship display
while a willing female may raise her raptorial legs away from their torso to signify this
(Gemeno 2006).
In this sexually dimorphic species, only the males are capable of hearing. They have a
single tympanum. Male mantids tend to use their wings more often, and the evolutionary
reasoning behind their hearing ability is that it helps them avoid predation by sonar wielding
predators such as bats. The female’s body is generally much larger in proportion to the
male’s while females tend to rely less on flight and more on ambush when seeking their next
meal (Fellman 1993). A ratio of 1.37:1 is the significant point at which cannibalism
between mantids can and does tend to occur in non-communal mantis species (Fagan 1996).
Cannibalism is by far, not limited to just praying mantids. In some shark species,
cannibalism occurs as early as the initial embryonic development until a single well-fed
shark embryo is left within the oviduct. With spiders, the newly emerging larvae sometimes
feed on the mother spider in times when food is scarce and the mother becomes their first
easily obtainable meal. In times of high levels of induced stress, parents of several bird
species as well as mammals, especially carnivores and rodents. Other instances of
cannibalism in rodents can be induced by the presence of an unfamiliar male which may eat
newly born young in order to induce the female rodent’s ability to go into heat. Some 138
species of animals have been recorded as having some form of cannibalism; this excludes
acts of cannibalsim out of necessity due to overcrowding or where stress was shown to
effect the organism’s behavior (Desmond 1991). While mantids tend to approach females
more readily when the female appears well-fed, some spiders, such as Nephila fenestrate
mount females during the female’s consumption of newly caught prey. Another species of
spider, Lycose tarantula (L.) approach during daylight hours, instead of at the night hunting
period, to reduce risk of cannibalism of a hungry female (Gemeno 2006).
In nature, it has been observed that cannibalism during mantis copulation occurs at a range
of 20 – 31% and supports the natural selection for anti-cannibalism between males of the
same species (Gemeno 2006). Some tropical mantis species, such as those which rely
heavily upon camouflage to avoid predation from birds and other large predators, only mate
during very brief periods at dawn. This transitional time allows the males to safely approach
the females with the newly approaching daylight while avoiding other sources of predation
as well. While it would seem more beneficial to mate at night under these circumstances, it
is important to note that mantids are a highly visual species and require at least a minimal
light source to allow the carefully planned out approach to their intended (Science News
1980). In situations in which male:female ratios vary substantially, there have been
significant variations in the number of approached mates by the male, as well as the duration
of copulation with a selected mate. A male chosing to mate with several females has the
increased risk of being cannibalized with each successive copulatory act, while males in
male biased populations tend to prefer a longer copulatory duration, rather than with
multiple females. In doing so, the male’s sperm is more likely to fertilize all of it’s selected
female’s eggs while only risking cannibalism from one female. It is also in the best interest
of females in 1:1 or female biased populations to not canniablize males in order to ensure
that they are able to mate and to ensure fertilization of all of their eggs in a given ootheca
(Prokop 2005).
Methods. – The experimentation was conducted under laboratory conditions during April
and May, 2008. A single ootheca was obtained “Carolina Biological Supply Company”
along with a single vial of Drosophilia melanogaster which accompanied them. D.
melanogaster are a universally accepted and used primary food source for mantis hatchlings
(DeShawn’s 2008). The fruit flies were placed in cold storage to slow their emergence
while the ootheca remained at slightly above room temperature for six weeks prior to
hatching. Upon progressing beyond the suggested emergence time of two weeks for the first
mantids nymphs, a small dissection of the ootheca was performed in order to ensure that the
ootheca did in fact contain living organisms. While some insect species require a period of
low temperature prior to a warming period, it has been noted that tropical species do not
require even a simulated ‘hibernation stage’. Without this hibernation stage, speices from
northern habitats will have a delayed emergence or perhapce none at all (Flemion 1936).
Upon confirming the ootheca had live organisms present, it was left in the warm office in
hopes of a promt emergence of the nymphs. Meanwhile, the culture media containing the D.
melanogaster had all but completely died off, with time constraints approaching, an
alternate food source needed to be chosen. A relatively large supply of milkweed bugs was
chosen to be added to the aquarium soon after the mantids emerged. At the time of their
emergence, the nymphs were four weeks past due, and one hundred and twenty-two mantis
nymphs were taken from their original enclosure and placed into a small plastic tub, and
shortly after, into a ~40 liter aquarium with cheesecloth for a breathable cover. Small twigs,
sticks, paper towels and bits of cheesecloth were added to the closure in an organized
fashion to provide a suitable habitat for the young nymphs. A petri dish lined with wet
paper towels was in one corner of the aquarium, while a watch-glass covered in wet paper
towels was placed in the far corner relative to the initial mantid placement. Observations
were periodically made with emphasis on mantis, prey interactions, and mantis, mantis
interactions. As the population drastically slimmed, the remaining ten matids were placed in
a much smaller plastic container (20 x 8 x 8)cm. This new habitat, nearly identical to the
first in every aspect except it’s size as a scaled down model of the first. Milkweed bugs less
than 0.5 cm., were added to this new encloser in hopes of increasing the predation rate by
the mantids in order to enhance survival rates. Mantis predation is drastically increased as
their predator to prey ratio of lenghts reaches 1.37:1 (Fagan 1996). Water supply was
changed daily, and a gentle water misting of the area was done daily as well. Observations
continued throughout the remainder of the mantid’s lives until the last one was left alone
with ample prey supply.
Results. – After six weeks of incubation, the emrergence of mantids from the ootheca
occurred on the 18th of April. Unfortunately, between the time of their emergence and the
first two days, all but thirty of the mantids died from either starvation, drowning, or inability
to successfully complete their initial molt. Nearly twenty percent of the initial population
died relatively close to the ootheca as they were unable to successfully complete their initial
molt as indicated by a thing white substance still attached to their legs or abdomen,
rendering them unable to acquire food and water. This is a naturally occuring phenomenon,
as it is generally seen that each instar along with the initial molt can be a significant cause of
death for a given population, especially in species with larger numbers of instars (Fagan
1996). As the population rapidly declined, the remaining mantids lived relatively longer.
While difficult to tell for certain, it is likely that those that survived had been able to catch
and feed on the intended food source of milkweed bugs. Several mantids were observed
lunging after the milkeed bugs, but none were actually observed eating their prey. Small
amounts of red coloring was observed in the abdomen’s of the remaining ten surviving
mantids, likely indicating their ability to catch and feed upon the red and black milkweed
bugs. Some mantids were observed aquiring water fom the moistened paper towels in the
water dish and the looking glass, while other mantids had become victim to the larger pools
of water which was an unseen hurdle that lead to about twenty-five percent of mantid
deaths. Environmental hazards also accounted for nearly ten percent of deaths, leading to
starvation as they became unable to access food or water. Excessive volume of the habitat
likely made it difficult for the mantids to locate their food as the remaining forty percent of
the population gradually died of starvation. As this was observed, however, the remaining
ten mantids were placed into the much smaller container where food and water sources were
relatively much closer to the mantids remaining. At this point, it is likely that those that
survived the longest, were those which acquired the prey small enough to be easily captured,
while larger prey was not preyed upon and left all but the last mantis to starve from inability
to locate the remaining smaller prey, or fitness levels inhibited their ability to succeed at
obtaining prey. The last remaining mantis was placed into a (7 x 4 x 3)cm container to
ensure prey proximity and availibility and continued to thrive throughout the remainder of
the observational period.
Discussion. – Taking a closer look at instances of sexually related cannibalism it can be
seen that it as far from the average occurrence and is generally not in the best interest of the
males or females to cannibalize at every possible opportunity. Males approach at rates up to
six times more quickly when risk of cannibalism is reduced in such an instance where the
female has recently consumed prey or is currently consuming a meal. Males are able to
determine this by watching the females clean their forelegs, witness the consumption firsthand or by the odor given off by the recent meal. In laboratory controlled studies, males
mantids were observed to approach a female by first becoming visually fixated on its
intended prior to slowly approaching without any obvious courtship displays. Even in the
presence of food near the female, the male still maintained visual fixation on the female
until the male did a flying leap to mount the female mantis. In trials where the intended
females were allowed to capture prey, males succeeded in copulating 75% of the time, while
females that were teased with food, only 25% of the males were successful in completing
copulation. In trials where the mounting and copulation were successful, males approached
at 8.6x faster when the females were presented with food and allowed to consume the prey
as opposed to females who were presented with prey and not allowed to consume it
(Gemeno 2006).
Another experiment conducted with mantids involved the comparison of three different
ratios of male:female in a controlled laboratory environment. Ratios ranged from 1:1 to 1:2
to 1:3 with increasing ratio of males with each condition. In trials with monogamous ratios,
cannibalism was higher than in the other two treatments. Monogamous with a cannibalism
rate of 30%, while 3:1 experienced only 10%. In trials with multiple females, however, the
males which successfully dismounted after copulation tended to attempt escaping rather than
breeding with the unmated female(s). In treatments with multiple males and a single female,
however, after the first male to copulate had finished, the remaining male(s) would also
attempt to copulate with the mated female. Also, in trials where the first male was attacked,
the remaining male(s) quickly approached the occupied female in response to the attack. In
trials with male bias, males tended to copulate for longer durations in a likely attempt to
completely fertilize the female’s eggs. Copulation in female biased treatments were
generally shorter in contrast to the male biased treatments. This is likely due to risk of
cannibalism of the unmated female while the male mates with its intended (Prokop 2005).
Due to the existence of size dependence in cannibalism, it is imporotant to note that in
closely approximated broods of mantids, earlier emergence can play a significant role in the
longevity of a given ootheca’s fitness levels. Mantids which hatch too early, when prey is
scarce, can result in high mortality rates from starvation and cannibalism. In the presence of
an abundance of food, cannibalism is less relied upon until the abundance diminishes or
dispersal of mantids allows the prey population to stabilize. Even among a single ootheca,
emergence can range up to several days and those emerging late will have a much greater
chance of being cannibalized even by their own siblings. In some cases, nymphs which first
emerged, may molt two or more times before the entire ootheca might finish hatching. This
can lead to as many as five different instars existing from a single ootheca. In these cases,
size ratios can reach up to 4.67:1 where nymphs are emerging significantly later than those
which first emerged. In separated populations of mantids where one is allowed cannibalism
and the other is limited to the equal amount of prey provided to the cannibalistic group.
After only 30 days, length of the cannibalistic group is nearly double, while the population
size is less than half of the non-cannibalistic. This in turn would allow the cannibalistic
group in the wild to become cannibalistic on the non-cannibalistic group and therefore have
a much greater overall fecundity. Due to the slower metabolic rate of larger mantids, they
are more capable of enduring periods of starvation which could mean the difference between
lasting until sufficient prey is available, opposed to their smaller counterparts. While
cannibalism greatly reduces population size, it is important to realize that what is bad for the
group actually gives a great advantage to those individuals who successfully survive into
adulthood. It is with these mantids of higher fitness that greater fecundity can be achieved
and earlier dispersal of new ootheca can occur. This brings up an important observation in
which several ootheca may be found in a given area where a female mantid has obviously
come along and place her ootheca in an area where it is likely that the other egg cases will
hatch earlier than hers. Since there is no vegetation preference as evidence by ootheca being
found on a variety of pant types and various hard surfaces, it can be concluded that there
must be other reasons for this conundrum. It has therefore been concluded that this is a
‘saturation’ defense against parasitoid attack on the ootheca which could very well be a
greater risk than the ‘fitness-endangering behavior’ of ootheca saturation (Fagan 1995).
It is unfortunate to note, that the food source was either too difficult for the mantids to
acquire, or too large, and the water level in the petri dish was too high for the mantids to
safely drink from in the experiment which we designed. These being the reasons behind the
majority of initially observed mantid deaths. It appears that these factors could be used to
ensure that following mantids raised could have a much greater chance at survival if they
were separated into much smaller containers in order to ensure prey proximity and
availability. Prey competition would be a non-issue, and cannibalism would be eliminated
as a factor for cause of death. Also, rather than using a water dish, a gentle misting, or the
use of wet towels appear to be the preferred methods for providing water for the mantid
nymphs. In order to sufficiently study cannibalism among non-communal mantids in a
laboratory setting, nearly constant observation would be needed in order to allow mantids in
continual contact with one another. Sufficient prey of the correct size would initially
support the young nymph population while mantids of great fitness would gradually
cannibalize those less fit or incapable of successfully preying upon the given food sources.
Only then, could sufficient observations related to cannibalism amongst this species be
properly observed, however given the huge appetite of this species, it would be quite
difficult to replicate this experiment as a field-accurate study and this study would gradually
make it a necessity to use field populations.
Works Cited
Anonymous. "Narrow Window on Sex." Science News (26 Apr. 1980): 263.
DeShawn. Mantiskingdom.com. n.d. 11 May 2008.
<http://mantiskingdom.com/index.php?main_page=page&id=8&chapter=1>.
Desmond, Morris. "A Taste for Their Own Kind." National Wildlife 29.4 (1991): 14-16.
Fagan, William F., and Garrett M. Odell. "Size-dependent Cannibalism in Praying Mantids:
Using Biomass Flux to Model Size-structured Populations." The American
Naturalist. 147.2 (1996): 230-268.
Fellman, Bruce. "Guess Who's Coming to Dinner." National Wildlife 31.2 (1993): p42.
Flemion, Florence, and Albert Hart-Zell. "Effect of Low Temperature in Shortening the
Hibernation Period of Insects in the Egg Stage." Contr. Boyce Thompson Inst.
(1936): 167-173.
Gemeno, Cesar, and Jordi Claramunt. "Sexual Approach in the Praying Mantid Mantis
Religiosa (L.)." Journal of Insect Behavior 19.6 (2006): 731-740.
McCommons, James. "Bug-Eating Machines." Organic Gardening 48.4 (2001).
Patterson, Kathleen J. "The Praying Mantis." Conservationist 47.6 (1993).
Prokop, P., Vaclav, R. Males Respond to the Risk of Sperm Competition in the Sexually
Cannibalistic Praying Mantis, Mantis religiosa. Ethology 111, 836—848 (2005).