Ground Beetles

We have a weakness for naming vast periods of time after dominant animal groups: thus the Age of Fishes, the Age of Dinosaurs, the Age of Mammals. Stephen Jay Gould pointed out the provincialism of these designations, noting that none of these groups individually or together contains the sheer number of species of the arthropods which make up about 80% of the million or so multi-cellular creatures. He even says that “Age of Arthropods” is a parochial concept when we consider the life-form that has dominated the planet since the beginning.

The Age of Reptiles had a lot of other things too, like bugs and flowers and birds and germs. The Cretaceous section of Rudolph Zallinger’s Age of Reptiles mural at Yale’s Peabody Museum.

If we must characterize a whole by a representative part, we certainly should honor life’s constant mode. We live now in the “Age of Bacteria.” Our planet has always been in the “Age of Bacteria,” ever since the first fossils—bacteria, of course—were entombed in rocks more than 3 billion years ago.

On any possible, reasonable or fair criterion, bacteria are—and always have been—the dominant forms of life on Earth. Our failure to grasp this most evident of biological facts arises in part from the blindness of our arrogance but also, in large measure, as an effect of scale. We are so accustomed to viewing phenomena of our scale—sizes measured in feet and ages in decades—as typical of nature.

Far be it from me to contradict the late, great Stephen Jay Gould, but all of these designations are merely done to illustrate some educational point, which might now be less important than when the names were first assigned. And while Gould has an argument (for example, the total biomass of “monerans” exceeds by many times the total biomass of all plants and animals, and always has), technically his argument is problematic because there is no valid taxon that includes “bacteria” and nothing else. This is because, as Gould himself acknowledged, what used to be called “bacteria” (single-celled organisms with no defined nucleus, lumped together in the Kingdom Monera) is a paraphyletic group. Carl Woese showed in the late 1970s from studies based on RNA sequencing, that “bacteria” actually fall into two very large Kingdoms (to use a term from the Linnaean system): originally Eubacteria and Archaebacteria, but now called Bacteria and Archaea.  Genetic analysis showed that Archaea was more related to Eukaryotes (organisms with a defined nucleus) than with Eubacteria. In fact, members of Archaea and Eukaryota have a common ancestor more recent than the common ancestor of Eubacteria and Archaea. So technically, Monera includes protists and all their descendants, including us. An “Age of Bacteria” really means nothing more than an “Age of All Things with Cells (as far as we know),” which really illustrates less of a point than “Age of Fishes.”

No one would mistake this oil painting for a pipe, but it’s safer to warn the viewer. René Magritte’s The Treachery of Images (La trahison des images, 1928–29).

Gould’s criticism also assumes that we mortals are unable to understand Alfred Korzybski’s point that a Map is not the Territory. While we all have to be on guard against this fallacy, probably even grade school children who were once taught about the Age of Fishes understood that there were things alive during the Devonian other than Fish and that Fish did not die out before the Age of Reptiles. (I am of course talking about the Golden Age of Education when teachers were not afraid of running afoul of the culture warriors who have affected a pose of studied ignorance to mask an agenda of ruthless reaction.)

This excessively detailed and unnecessary digression is used soley to introduce a very small point (and to forestall all objections to making it): If you were going to characterize the age from the end of the Great Dying of the Permian Extinction to the present, there is a good case to be made for calling it the Age of Beetles. Looking at living things not just as contributors to undifferentiated biomass but rather as members of a unit of individuals capable reproducing individuals also members of that unit (i.e., a species), then beetles are fabulously spectacular. The order they comprise, Coleoptera, is the largest order* in terms of species among animals. There are some 400,000 species of beetles currently described, and it is thought that living beetles might total 1 million species, perhaps many more.

But numbers don’t tell the whole story. For those not impressed by J.B.S. Haldane’s remark that God was “inordinately fond of beetles,” you need consider perhaps a higher authority, Charles Darwin.

Darwin was an obsessive beetle collector. It seemed to be his one driving force before he figured out a direction for his life. Beetle collecting was something of a fad in Victorian England. (At the time, England had not heard of Pokemon Trading Cards.) Darwin, however, was more obsessed than most. In his autobiographical sketch (which among other places can be found in the first volume of his Life and Letters edited by his son Francis Darwin) Darwin related an anecdote about his youthful collecting mania:

But no pursuit at Cambridge was followed with nearly so much eagerness or gave me so much pleasure as collecting beetles. It was the mere passion for collecting, for I did not dissect them, and rarely compared their external characters with published descriptions, but got them named anyhow. I will give a proof of my zeal: one day, on tearing off some old bark, I saw two rare beetles, and seized one in each hand; then I saw a third and new kind, which I could not bear to lose, so that I popped the one which I held in my right hand into my mouth. Alas! it ejected some intensely acrid fluid, which burnt my tongue so that I was forced to spit the beetle out, which was lost, as was the third one.

I was very successful in collecting, and invented two new methods; I employed a labourer to scrape during the winter, moss off old trees and place it in a large bag, and likewise to collect the rubbish at the bottom of the barges in which reeds are brought from the fens, and thus I got some very rare species. No poet ever felt more delighted at seeing his first poem published than I did at seeing, in Stephens’ Illustrations of British Insects, the magic words, “captured by C. Darwin, Esq.” I was introduced to entomology by my second cousin W. Darwin Fox, a clever and most pleasant man, who was then at Christ’s College, and with whom I became extremely intimate. Afterwards I became well acquainted, and went out collecting, with Albert Way of Trinity, who in after years became a well-known archaeologist; also with H. Thompson of the same College, afterwards a leading agriculturist, chairman of a great railway, and Member of Parliament. It seems therefore that a taste for collecting beetles is some indication of future success in life!

Not to contradict Darwin, but it is also possible that going to Cambridge or Trinity in Victorian England was also an indication of sorts. (Incidentally the story from his autobiographical essay, which he wrote for his family in 1876, is remarkably consistent with his description of the event in a letter to Leonard Jenyns, October 27, [1846], but in the letter he noted that the two beetles he first collected were “carabi” (ground beetles) and the third was “a sacred Panagæus crux major.” The incident must have been firmly implanted to have recalled it vividly some 15 years after the event, and then to recall it in his autobiography 30 years after that.)

Darwin’s beetle collection is now at Cambridge’s Museum of Zoology. (Photo by Martin Parr. Guardian online, Nov. 1, 2008.)

Darwin made use of his collection-obsession when visited South American on the H.M.S. Beagle. Fossils, among other things, were sent back en masse to the Royal Society, which had Richard Owen do the formal descriptions. But he never lost his first love. He said late in life he could remember the exact spots he found certain specimens. When a son showed him a beetle he captured, Darwin instantly knew what it was even though he had not looked at beetles for 20 years.

Darwin’s letters from South America talks of his beetle hunts and throughout his other correspondence there are occasional references to what a beetle hunter he used to be. Francis found a scrap of paper recording how the existence of wings under a beetle’s elytra (the group’s characteristic ridged forewings), like the existence of a male nipple, argue for descent rather than special creation:

When one sees nipple on man’s breast, one does not say some use, but sex not having been determined—so with useless wings under elytra of beetles— born from beetles with wings, and modified—if simple creation merely, would have been born without them.

Francis mentions how his father tried to instill the passion of beetle collecting in his three boys:

About this time [1858-59] my father revived his old knowledge of beetles in helping his boys in their collecting. He sent a short notice to the Entomologist’s Weekly Intelligencer, June 25th, 1859, recording the capture of  Licinus silphoides, Clytus mysticus, Panagaeus 4-pustulatus. The notice begins with the words, “We three very young collectors having lately taken in the parish of Down,” etc., and is signed by three of his boys, but was clearly not written by them. I have a vivid recollection of the pleasure of turning out my bottle of dead beetles for my father to name, and the excitement, in which he fully shared, when any of them proved to be uncommon ones.

Francis appends to this anecdote an extract of a letter from Darwin to his relative, friend and mentor Rev. William Darwin Fox (November 13, [1858]):

. . .W., my son, is now at Christ’s College, in the rooms above yours. My old Gyp, Impey, was astounded to hear that he was my son, and very simply asked, “Why, has he been long married?” What pleasant hours those were when I used to come and drink coffee with you daily! I am reminded of old days by my third boy having just begun collecting beetles, and he caught the other day Brachinus crepitans, of immortal Whittlesea Mere memory. My blood boiled with old ardour when he caught a Licinus—a prize unknown to me . . .

So you have it on the authority of God, Haldane and Darwin that beetles should be cherished. I bring all this up to recommend the special issue of ZooKeys, published online May 20, 2011, devoted entirely to the Carabid beetle, commonly called ground beetles. Ground beetles or carabids are members of the family Carabidae, which itself is part of the superfamily Caraboideae (members of which are caraboids). Carabid species number about 40,000 (or about 10% of described beetle species). They are characteristically black or shiny metallic colored and have ridged elytra, some of which (as Darwin noted in the quote above) are hardened and fused, rendering the animal unable to fly. In this respect they are unlike cockroaches which they superficially resemble, because the latter have leather or no forewings. They typically have grooved forelimb tibia (the second most distal, or farthest from the body, leg segment) which have hairs for cleaning antennae. Their heads are usually smaller than their thorax, and their antennae are thread-like. Like other adephagans (like tiger beetles and whirligig beetles) carabids have paired pygidial glands located postero-dorsally (i.e., towards the back and underneath) in the abdomen, which are used for secreting chemicals as a defense against enemies such as toads or Darwinian collectors. A famous group of carabids in this regard are the bombadier beetles, which can fire a chemical gas from their pygidial glands with a popping sound and smoke-like puffs. Carabids live in the soil and are almost universally considered beneficial to man, since they are predators on soil insects and invertebrates, including agricultural pests.

A quick note on the journal: ZooKeys is an open access, peer-reviewed journal specializing in systematic zoology, phylogeny and biogeography and edited by Smithsonian entomologist Terry Erwin. Unlike the Big Science Empires of Science and more especially Nature, ZooKeys actually encourages the distribution of its papers freely and without advance permission. It’s almost like they believe science is a public good that ought to be shared. It is a concept so radical that surely someone must shut it down. We know that research is only done in the hopes of obtaining monopoly profits. And just because the authors to publications run by the Nature Group aren’t paid and the editors also volunteer their time, that is no reason why the journal owners should not charge as high a price as they can conceive for the work of others. This is clearly a better model for scientific progress.

The newly described Eucamaragnathus desenderi with a detailed view of the ridged elytra. Click to enlarge.

But I digress. The special issue is dedicated to the memory of two Belgian biologists who did significant work with ground beetles: Konjev Desender (1956–2008) and Jean-Pierre Maelfait (1951–2009). You can read the memorial by Gábor L. Lövei. The issue has 30 separate papers, beginning with a large overview of the research on carabids over the last 40 years. Two new ground beetles were described and both named in honor of Konjev Desender: Eucamaragnathus desenderi from eastern and southern Africa; and Calleida desenderi of Ecuador. (I have to admit I haven’t the slightest idea in what respect either of these beetles are remarkable, if at all, so you’re better off reading the papers yourself.)

Female Calleida desenderi, dorsal view. Click to enlarge.

The rest of the issue ranges over environmental, behavioral and biogeographical issues relating to ground beetles with an emphasis on how they can serve as environmental indicators. There are far too many papers for me to describe them all, so for that you will have to refer to the table of contents. I’ll just highlight a couple of things that caught my interest right away.

First, Evgeniy Zinovyev of the Institute of Ecology of Plants and Animals, Ural Branch of the RAS, Ekaterinburg, Russia, has a paleontological study of the ground beetles from 33,000 to 22,000 years ago in the area from the Ural Mountains in the south to the northernmost parts of western Siberia in Russia: “Sub-fossil beetle assemblages associated with the ‘mammoth fauna’ in the Late Pleistocene localities of the Ural Mountains and West Siberia,” 100 ZooKeys 149-69 (2011) (paginated pdf file). Subfossils are remains of organisms that have not completely fossilized. Most subfossils come from the Quaternary Period and represent remains which have not had sufficient time to fossilize completely. In this case the subfossils are isolated chitin fragments. What Zinovyev does is compare the environment that the species of insects live in today with analysis of the plants and animals that are represented in the fossil record with these subfossils in order to “estimate the factors possibly determining the composition of insect species in the past, including the influence of the large herbivorous mammals.”

The time period that the remains come from in this area is the Pleniglacial (a term used in Europe; we would use the age Late Pleistocene). This was the during the period of “mammoth fauna” including mammoth, bison, wooly rhinoceros, giant deer, reindeer and wild ox. The climate during the time was colder than present and variable. The subfossils studied were from 13 sites, which included arctic, sub-arctic, “mixed” and boreal types paleo-environments.

Zinovyev concludes that the mix of insects depended not only on the climate but also on the mega-fauna. The large herbivores turned environments into savannas with abundant herbal vegetation including cereals by inhibiting the regrowth of forests (by eating the undergrowth) and by destroying (with their hooves) the moss cover in taiga and tundra areas. The paper explains how the different insect assemblages were distributed in northern Europe, western and eastern Siberia, depending on climate and type of mammal herbivory.

Gil Wizen and Avital Gasith of the Department of Zoology, Tel-Aviv University, have a paper on the predation of two species of Epomis beetles on amphibians in Israel: “Predation of amphibians by carabid beetles of the genus Epomis found in the central coastal plain of Israel,” 100 ZooKeys 181-91 (2011) (paginated pdf file). There’s no need for me to say anything if there is a grisly photo, and fortunately there are six of them.

Predation of amphibians by adult Epomis: a) Bufo viridis juvenile by Epomis circumscriptus; b) Hyla savignyi juvenile by Epomis circumscriptus; c) Bufo viridis juvenile by Epomis circumscriptus; d) Salamandra salamandra infraimmaculata metamorph by Epomis dejeani; e) Hyla savignyi juvenile by Epomis circumscriptus; f) Triturus vittatus metamorph by Epomis dejeani (photographs by Gil Wizen).

I’ll simply add that I have seen beetles devouring the carcass of a frog (it’s not for the faint of heart), but I had always assumed they simply scavenged a dead animal. The authors here, however, did lab experiments to show that these ground beetles actually attacked live amphibians. (A long time ago I had a friend that did those sort of experiments. He did not grow up to be a biologist, however.)

I will mention one more short study before you go off to read the issue yourself. Anita Giglio, Pietro Brandmayr, Federica Talarico and Tullia Zetto Brandmayr of the Department of Ecology, University of Calabria have communication which summarizes current knowledge on the exocrine glands of carabids: “Current knowledge on exocrine glands in carabid beetles: structure, function and chemical compounds,” 100 ZooKeys 193-201 (2011) (paginated pdf file). The secretions of these glands have various functions among the beetles themselves and as defensive measures against predators.

I found most interesting the defensive secretions of the pygidial glands. The authors speculate that oozing was the original delivery system (or as they say “the plesiotypic mode of discharge”) and only later were means for spraying and “crepitation” devoloped. They say that some researchers have found that in addition to defense the secretions from these glands have antimicrobial and antifungal purposes and act as alarm messages. The various components of the ooze or spray include: hydrocarbons, aliphatic ketones, saturated esters, formic acid, higher saturated acids, unsaturated carboxylic acids, phenols, aromatic aldehydes and quinones. Certain bombardier beetles (Brachinus species) release irritating quinones “by the oxidation of hydroquinones in a double-chambered apparatus . . . a certain amount of heat and the explosion associated with the reaction reinforce the defensive effect.” Tiger beetles produce benzaldehyde. The carabid beetle Galerita lecontei secretes, as a spray, a mixture of formic acid, acetic acid and lipophilic components. Pterostichus californicus synthesizes tiglic and ethacrylic acids from isoleucine. Two species of ground beetles (Ardistomis schaumii and Semiardistomis puncticollis) produce complex monoterpenes for defensive secretions.

I should mention one other feature that all ZooKeys articles share: They participate in the Encyclopedia of Life project and the taxa newly described in ZooKeys is immediately entered into the Encyclopedia. Moveover, the taxa mentioned in the articles are hyperlinked to: its Pensoft Taxon Profile; the Global Biodiversity Information Facility; the National Center for Biotechnology Information; the Encyclopedia of Life entry; the Biodiversity Heritage Library and any Wikipedia entry among other references. The journal needs to be better known among the public interested in zoology.

____________________

*I use Linnaean hierarchical terms because I’m too old to forsake them, and because they at least imply a vague notion of the relative nesting of one group in another (and thus imply degrees of relatedness through descent). Plus it’s just easier to say the Super-Order Dinosauria than “the latest common ancestor of the pigeon and triceratops and all its descendants.” I realize that just like “Age of Reptiles” hierarchical taxonomy is somewhat misleading, but frankly there are bigger problems to worry about.

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  1. September 17th, 2011

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