Past episodes of Critter Corner have dealt with some of the mammals, reptiles, and amphibians of GPFWA. One might claim that I have missed the boat by not acknowledging the presence, and importance, of members of the largest taxonomic group of animals on the planet – the insects. Fans of these creatures would have a good argument. With nearly one million described species, the insects make up around 80% of all the species in the animal kingdom. I would argue that they are also the most biologically successful fauna on the planet as well.
We humans commonly measure success in terms of social status, income, political influence, or by our contributions to the common good. But, how do we measure biological success?
It could be said that simply avoiding extinction, existing as a living species, is the mark of biological success. But this definition of success is not as straightforward as it might seem. Consider a group such as the dinosaurs. Extinct today (unless one counts their saurischian descendants, the birds), they were the dominant class of vertebrates on earth for 180 million years. This long tenure and their remarkable variety make it a bit difficult to think of them as a biologically unsuccessful group.
Perhaps using a series of measures would give us a clearer picture of a group’s degree of biological success? So it is that biologists typically examine four parameters in measuring the biological success of a given taxon or a species. These factors are geologic distribution, geographic distribution, number of species, and number of individuals.
The geologic distribution of insects as determined by the fossil record reaches far back into deep time. The oldest fossil insects are nearly 400 million years old. In comparison, the oldest whale fossils date back about 50 million years and the fossil hominid Australopithecus three million years. So, as a group, insects have been around for quite a spell. They are exceedingly successful by this standard.
In terms of geographic distribution, the insects are again phenomenally successful. They are found on every continent on earth as well as in every imaginable habitat. Granted, they are rare in Antarctica and are outnumbered in the oceans by the crustaceans. But visit any country on earth, any biome within that country, and you are likely to encounter insects in abundance.
I have already noted the tremendous species diversity found among the insects. There are 200 times more insect species than mammal species and they outnumber both the birds and the reptiles by a power of 100. This is again a highly positive manifestation of biological success.
I would venture to guess that many of you, watching a swarm of midges or a marching column of ants, have wondered just how many insects there are in the world. Of course it is only an estimate, but my quick search on the Internet (www.si.edu) yielded an estimate of 10 quintillion individual insects alive at any one time. That’s a 10 followed by eighteen zeros. Incidentally, if we could weigh all the insects alive on earth at any one time, their biomass would be greater than that of all the vertebrates – elephants and whales included. By the standard of number of individuals, insects are again a highly successful group indeed!
Of course there are many, many insects I could choose as the first Critter Corner representative of their kind and I do hope in future to include more. But let me begin with one of my favorites – the Praying Mantis. Perhaps mantises, or mantids, would be a better term since there are over 2000 species worldwide. Like most other animal taxa, the mantids have achieved their greatest species diversity in the tropics. At Goose Pond FWA, you are likely to encounter only a couple of species. These are the native Carolina Mantis and the introduced Chinese Mantis.
Perhaps, as an impressionable 11 year old, I shouldn’t have watched the 1957 sci fi classic The Deadly Mantis. (trailer at www.youtube.com/watch?v=UBos7oKAn_w). Henceforth, I was mesmerized by the frightening visage and voracious feeding habits of this animal. Even today, many decades later, I cannot encounter a Praying Mantis and resist the urge to stop, observe, and simply contemplate its exquisite adaptations for the lifestyle of a top predator. Recalling scenes from the movie, I can readily anthropomorphize the reaction of a hapless butterfly confronted by a ravenous mantis. They really do make a nightmarish science fiction “monster”. Mantises are stealthy, quick to strike, powerful, and rapacious; what a combination.
And, before we go any further, what about that name? Doubtless you have seen these insects also referred to as a Preying Mantis. I have not been able to determine which is preferable or even most appropriate. The website What’s That Bug? (www.whatsthatbug.com/2006/10/29/preying-versus-praying/)
suggests this is a classic example of why biologists prefer to use scientific names. A species will have only one scientific name no matter what language is being used in the discussion. Praying Mantis seems to me to be the more commonly used appellation. This is in reference to the oversized forelegs legs which are powerfully developed, and fearfully armed with spines in order to grasp their prey. At rest, these legs are held in a position which reminds one of a prayerful posing of the arms and hands, thus the common moniker.
Most mantids are ambush hunters which lie in wait with their ferocious forelimbs held upright poised to snatch any unwary prey that comes within range. They most commonly feed on other insects such as flies, bees, butterflies, crickets, and grasshoppers. Mantids may be cannibalistic and some species are large enough to tackle small birds and lizards. Since Praying Mantises rely on sight to hunt they are most active in the daytime (diurnal). Their vision is well-developed and stereoscopic at close range. The peripheral units of their compound eyes are quite sensitive to motion. This helps them detect their prey and they can swivel their head to more closely focus on a potential food item. I think this ability to turn the head and look back at us is one of their most fascinating adaptations. It seems to me to give them an aura of intelligence that is normally missing when compared with the expressionless, unmoving eyes of a typical insect.
Praying Mantis adults are killed by the onset of freezing weather and the next generation overwinters as eggs. These are protected within an egg case (oothecum) that very much reminds me of the foam insulation one can buy in a pressurized can. The frothy eggs case is secreted around the eggs as they are laid and soon hardens into a protective covering. You may find these by wondering about in old field or prairie habitat and looking for the brownish, foam-like case attached to a plant stem. These egg cases usually have the appearance of accordion folds on their surface. I have collected these in the spring, held them in a jar, and been rewarded with the amazing sight of hundreds of tiny, miniature Praying Mantises scrambling about upon emerging from the oothecum. Releasing these into one’s garden provides a natural deterrent against insect pests too.
Praying Mantises have their enemies. Arthropods such as spiders and ants will attack them. Vertebrates including frogs, lizards, and birds will also eat mantises. Although mainly diurnal, mantises may sometimes fly at night. They are attracted to lights and males may travel nocturnally in search of females. At this time, bats may prey on them. Research has shown that some mantises have the ability to hear the echolocation sounds produced by bats. Upon detecting a foraging bat, such mantids will begin a series of descending, avoidance spirals toward the ground (en.wikipedia.org/wiki/Mantis).
Praying Mantises commonly avoid predators through protective coloration or camouflage. The green of the Chinese Mantis for example enables it to seamlessly blend with the vegetation upon which it sits. Among other mantis species, mimicry may have evolved. Often these protective disguises are extreme with the mantis physically resembling a leaf or a flower. These masquerades remind us of the power of natural selection to shape earth’s fauna and flora in ways that enhance their owner’s chances of survival.
Though certainly not to be seen at GPFWA, I close with a striking example of mantis mimicry. One of my favorite Praying Mantis species is the Southeast Asian form known as the Malaysian Orchid Mantis. Although not obligated to perch upon orchids, the structure
and coloration of this species allows it to stealthily lie in wait upon a flower for the unwary approach of a potential meal. An insect may even mistake the mantis for a flower and glide with intention toward its demise. This species is a wonderful example of the stunning variety, delicate beauty, and mind-boggling adaptations we find among the insects we call Praying Mantises.