Meet the Beetles and Other Bugs That Bite Their Bark
From the first humble beetle (order Coleoptera) arose a vast multitude of descendants. Modern tropical forests are home to possibly tens of millions of beetle species, and some published estimates suggest that there may be as many as thirty million to fifty million, an overwhelming number that has led entomologist Mark Moffett to describe earth as the “planet of the beetles.”13 To what do these insects owe their astronomical success? They alone have developed the ultimate body armor while maintaining the benefits of flight dispersal. A beetle’s front wing is modified into a hard shell, known as the elytron, which covers the hind wing when it is at rest. When a beetle flies, its hind wing unfolds into one that is larger than the front, and flight is powered entirely by these extended back wings: an unusual arrangement called posteromotorism. The shell-like front wings are held outstretched and can only generate lift, glider-style.
During the Late Permian there were only a few groups of beetles, about six families, and they all belonged to the most primitive suborder of beetles. They were the first wood-boring insects, living in the forest undergrowth where they buzzed and flew from one fallen dead tree to another. Their hard armored bodies protected them from insect predators while they chewed into damp decaying wood to lay eggs; this environment sheltered their larvae, wood-boring grubs, from dry air and sunlight. The beetles were among the first organisms to feed on lignin and cellulose by mixing wood with fungi.
FIGURE 6.3. A beautifully preserved fossil of Liomopterum ornatus (family Liomopteridae) from Permian rocks of Kansas with well-developed paranotal lobes on the first thoracic segment. This neopteran (new-winged) insect family was another casualty of the Permian extinctions. Formerly placed in the Protorthoptera, these insects are now regarded as likely stem-Plecoptera. While they became extinct, their aquatic, stream-dwelling stonefly relatives (order Plecoptera) survived and flourished. (Photo by Frank Carpenter. Museum of Comparative Zoology, Harvard University. © President and Fellows of Harvard College.)
Bark lice (order Psocoptera) joined the first beetles in the deadwood. Tiny voracious insects with chewing mouthparts and gradual metamorphosis, bark lice gnaw on organic materials under the loose bark of dead trees and can congregate in massive numbers. Their modern cousins, the book lice, will feed on paper, and if undetected they can completely destroy library books. During the Late Permian, bark lice and the first beetles teamed up with wood roaches and fungi to help quickly decompose and recycle nutrients from dead forest trees and leaf litter.14
One Main Suspect?
Many insect species may have gone extinct during or near the end of the Permian, but virtually all the orders with complete metamorphosis survived, as well as many others with gradual metamorphosis, such as bark lice, thrips, and homopterans. Only one order with complete metamorphosis, the tiny and scarcely known Miomoptera, vanished then. Two other small groups, the little-known orders Glosselytrodea and Paratrichoptera, endured beyond the Permian–Triassic boundary and became extinct much later, during the middle Mesozoic era. Maybe they were not able to adapt to the Mesozoic’s environmental changes. Maybe they were exterminated by the warm-blooded dinosaurs. Maybe they were failures, or maybe they just evolved into more modern groups. Whatever happened to the Glosselytrodea and Paratrichoptera doesn’t really matter here. The key point is that they survived the Permian.
So did a lot of the other orders, which went on to diversify and are now common. Some insects, like the Homoptera, Neuroptera, Coleoptera, and Mecoptera, enjoyed substantial species richness in the Late Permian, suffered some declines, but carried on successfully into the Triassic years. Other groups, the Trichoptera, Lepidoptera, and Diptera, had low diversity but nevertheless survived the end-Permian holocaust. They are currently among the most species-rich orders. Why did they survive? The idea that low-diversity groups, like the trilobites, are particularly prone to extinction does not seem to apply here. Some of these groups could have lived on happily, provided that they had pioneered ecological niches in unaffected habitats and had an arsenal of survival skills, like complete metamorphosis. The suspect in the Permian killings must be some kind of selective agent. We are looking for a killer that could wreak havoc on coral reefs and massacre the coastal lowlands but leave the upland communities in comparative bliss.
Perhaps one factor ties together the multifarious elements of this story. We still need to consider our old friend plate tectonics, also known as continental drift. You may have already read or learned about continental drift,15 and you may recall that before the present continents were configured, there was a time during the Early Mesozoic when the northern continents were joined in a landmass called Laurasia, and the southern ones in a landmass called Gondwana. You may recall also that prior to that time all the land areas were united in a single vast supercontinent called Pangaea. Present-day North America was wedged directly into South America, Africa, and Europe, and present-day Africa, most centrally located, was directly connected with North America, Europe, Asia, South America, Antarctica, India, Saudi Arabia, and Australia. Although many people mistakenly assume that this massive land aggregation was the starting point for continental drift, that’s not the case at all. It’s just the origin of our modern arrangement of continents. Pangaea first formed during the Early Permian, when more ancient continental configurations aggregated, and after parts later broke away, it reformed again in the Middle Triassic. It took millions of years to assemble and corresponds suspiciously closely to the end-Permian extinction event.
As islands and continents collided, previously separated areas were merged. This would have reduced marine areas by eliminating shorelines and their wetland communities, and it would have brought different communities of plants and animals together. When these groups mixed, competition would insure that some species would dominate and become “weedy” and widespread, while other, less-aggressive species that formerly survived in isolation would be driven to extinction. As larger continental masses collided and fused together, these processes would have accelerated. Volcanic eruptions might have been triggered; inland, new mountains would have been uplifted and new rivers and streams would have emerged, ripe for insect colonization. As the land area became larger, the global climate changed. Inland areas became hotter and drier. Some plants and animals, like the insects with complex metamorphosis, were better able to adapt to these shifting environments.
Can Pangaea alone explain the Permian extinctions? As compelling as those arguments sound, the current answer is “no.” In past decades we used to think that the extinctions took place over millions of years, but careful studies of Permian period sediments in China by Douglas Erwin and other scientists has narrowed the interval of the end-Permian extinction down to a mere hundred thousand years or less. That may seem like a long time, but it is way too fast for plate tectonics alone to have been the main culprit. However, I still think it’s important to recall that they may well have been a key factor in many of the terrestrial insects’ successful diversification. Pangaea’s formation helped bring about the Permian’s arid terrestrial climate, which is usually tagged as the reason for the holometabolous insects’ rapid evolution then.
The end-Permian extinctions don’t look like a single event or a fast event caused, for instance, by an asteroid impact. Cosmic collision enthusiasts have been searching the planet for geological evidence for more than thirty years, but they have found nothing definitive. They haven’t identified an impact crater or impact debris from this time period. Moreover, the Permian–Triassic boundary layer lacks iridium, which is contrary to what is expected for an asteroid impact. Claims of the discovery of fullerenes (“buckyballs”) in the Permian–Triassic boundary layer have filled collision enthusiasts with excitement, but these reports have been contested and are unrepeated. Impact supporters have even gone so far as to suggest that an asteroid collision may have triggered the Siberian volcanic events, which in turn obliterated the impact crater. That’s
a really sexy idea, but it still lacks good evidence. The philosopher Alfred North Whitehead has advised us to “seek simplicity and distrust it.” His advice seems good in this case. We will keep seeking a simpler explanation for the end-Permian extinctions, as that is the nature of science, but for now they still appear to be complicated.
During the Permian years, insects suffered their most catastrophic setback of all time. In telling the tragic tale of the fall of the old-wings and gigantic air dragons, it’s easy to forget the flip side of that story. Despite all the species and orders that died then, lots of others lived on, and they speak volumes about the insects’ resilience and adaptability. Most of the survivors were species with novel adaptations, such as advanced neopterous wing flexing and complex metamorphosis. The new-winged insects with wing-folding mechanisms could fly faster, hide better, and outcompete the old-winged insects. New feeding innovations like the invention of refined fluid feeding mouthparts allowed insects to successfully colonize different plants in upland areas. The evolution of larval stages enabled them to invade plant tissues and more successfully avoid large predators. Insects proved themselves resilient in the face of continental collisions, global climate change, massive volcanic eruptions, and substantial geochemical changes in the oceans. In fact, despite the challenges they encountered while colonizing the land during the Silurian years, insects proved in the Permian that the conquest of land was a winning strategy. As cockroaches demonstrated to the trilobites, if there was ever a good time not to be in the oceans, it was during the end of the period.
Maybe it’s perilous to divide the history of life into separate ages, but in this case perhaps we can indeed pick one singular moment when the Paleozoic era came to an end. I’d choose the particular day when the final trilobite died. What other creature better symbolizes the entire era than the trilobite? Their reign in the oceans lasted for more than 300 million years, but some 252 million years ago, on a cloudy morning perhaps, the last one stopped feeding in a shallow tidal pool. Her body floated to the surface, and the retreating tide washed it ashore along with other trilobite carcasses. Where were the black birds of death? Who witnessed that event? There were no shore birds on that lonely beach, but there was a scurry of small feet, as first one cockroach, then another, found the castaway body and consumed it. Maybe a lone beetle, preening its antennae on a log nearby, briefly flew down to inspect the scene and partake in the feast. Then it turned, unfolded its wings, and buzzed clumsily into the forest. The Paleozoic years had ended, to quote the poet T. S. Eliot, “not with a bang but a whimper,” and the insects declared themselves the victors. But soon there would be a new rustling in the Mesozoic forests; with slashing claws and gnashing teeth, the first dinosaurs would appear. How would the insects get along with their new roommates?
PLATE 1. The disruptive coloration of the malachite butterfly, Siproeta stelenes, provides excellent camouflage in the dappled understory of the tropical dry forest at Chamela Biological Station in Jalisco, Mexico. Examples of the largest butterfly family, Nymphalidae, they fly rapidly when disturbed.
PLATE 2. Can you see it? Motionless on a leaf, this Ecuadorian katydid nymph (order Orthoptera, family Tettigoniidae) displays remarkably cryptic green coloration. (Photo by Angela Ochsner.)
PLATE 3. Stalking the mossy Ecuadorian cloud forest at night, this well-camouflaged praying mantis nymph (order Mantodea) uses crypsis to its advantage while hunting insect prey. (Photo by Andy Kulikowski.)
PLATE 4. Hiding in plain sight, this very cryptic katydid demonstrates another method of camouflage: by resembling tree bark it is well adapted to surviving the prolonged dry season at the Chamela Biological Station in Jalisco, Mexico.
PLATE 5. Seemingly confident in its ability to rapidly jump away from danger, this Ecuadorian short-horned grasshopper (order Orthoptera, family Acrididae) is sitting pretty at the Yanayacu Biological Station in Ecuador. (Photo by Angela Ochsner.)
PLATE 6. Voracious predators of other insects, the assassin bugs (order Hemiptera, family Reduviiidae) impale their prey with their piercing mouthparts and suck out the fluids. (Photo by Angela Ochsner.)
PLATE 7. Literally stuck in one place, the sap-feeding spittlebug nymphs (order Homoptera, family Cercopidae) cover themselves with bubble-laced honeydew. This Ecuadorian species may acquire defensive chemicals while feeding, since it also displays bright aposematic warning coloration. (Photo by Angela Ochsner.)
PLATE 8. These Altinote neleus butterflies (family Nymphalidae) commonly gather roadside at mud puddles on sunny afternoons at the Yanayacu Biological Station. Perhaps overly confident in their toxic defenses and aposematic coloration, they can be picked up by hand and will exude orange toxic fluids from their bright abdomens. Although they are well evolved against predation, they have not adapted to the modern world and are often run over by passing vehicles. (Photo by Angela Ochsner.)
PLATE 9. Seldom seen by daylight, the enormous tusk-jawwed males of Corydalus hageni (order Megaloptera, family Corydalidae) sometimes fly to lights at the Yanayacu Biological Station.
PLATE 10. A pair of brightly colored tortoise beetles (order Coleoptera, family Chrysomelidae) display just the right combination of body armor, defensive chemicals, and aposematic coloration to leisurely feed on leaves in the Ecuadorian cloud forest. The chrysomelid leaf beetles are a highly successful group of plant feeders in the New World tropics. (Photo by Angela Ochsner.)
PLATE 11. Careful handling this one! The caterpillar of a hemileucine saturniid moth (family Saturniidae) displays its defense mechanism: brittle, hollow spines loaded with irritating toxic chemicals. This approach works well to protect these caterpillars from predation by birds and other vertebrates but does nothing to defend them from parasitism by small wasps and flies. (Photo by Jennifer Donovan-Stump.)
PLATE 12. Large adults of Automeris abdominals are frequent visitors to the lights at the Yanayacu Biological Station. By day they rest with their brown forewings covering their hind wings, rendering them very cryptic on leaf litter. When disturbed they reveal the bright hind wings with large eye spots, which may induce a startle response in predatory birds. (Photo by Angela Ochsner.)
7
Triassic Spring
April is the cruelest month, breeding
Lilacs out of the dead land, mixing
Memory and desire, stirring
Dull roots with spring rain.
T. S. ELIOT, The Waste Land
It’s difficult to judge the seasons in Wyoming. In June, sporadic rain transforms the prairie grassland into an endless vista of emerald green, which waves in the wind like a vast ocean. At higher elevations the mountain meadows are awash with red, yellow, and blue wildflowers, which overnight might be buried under a snowfall. By July, the summer drought quickly dries out the grasslands and flowery fields, and the prairies and meadows turn golden brown for another ten months. Even so, in mid-July, it’s not unusual for a hailstorm to cover the ground with ice pellets.
The trees unfortunately don’t help much. Deciduous ones like aspens and poplars don’t leaf out until late May or early June. Autumn comes early. The first killing frost usually occurs in mid-September, and the fierce Wyoming winds quickly strip the trees of dead leaves by early October. The broadleaf trees tend to be without leaves for a full eight months. If you judge the winter by when the trees are bare, then it lasts a long time.
It’s not so easy to judge by snow, either, which at high altitudes can come during any month. Our heaviest storms tend to arrive very early in the fall or late in the spring, burying Wyoming in white crystal flakes in October or May. If that’s not confusing enough, some of the most pleasant weather is liable to show up in midwinter. On most days in January or February, the skies will be totally clear and luminous azure blue. The winds tend to blow away the snow, or it desiccates in the dry air, so long stretches of winter may be totally without any snow cover.
Anyone who has lived in Wyoming can probably understand T. S. Eliot when he wrote that “Apr
il is the cruelest month,” as the onset of spring is particularly hard to judge. On sunny days, tulips and daffodils rapidly shoot up, usually to get frozen in ice or buried under snow. There are two other indicators of spring aside from the first flowers, and they’re especially significant because they remind us of the Triassic years, 252 to 201 million years ago. The first is the traditional one: the appearance of robins and other migratory birds. In my home state of Michigan, the robin is indeed a pretty good sign of mild spring weather. Wyoming is crueler: more often than not, this bird appears all puffed up, and desperately tries to keep warm by hiding among the snow-laden spruce boughs during a late spring blizzard. But why would robins remind us of the Triassic?
When I was a child, birds were birds and dinosaurs were thought to be great reptiles. How times have changed. We now understand the message of the wishbone: birds are direct descendants of the dinosaurs, the most famous of all groups which originated during the Mesozoic era.1 The dinosaurs first evolved during the Triassic years, and the feathered dinosaurs and first birds arose during the Jurassic; while the big dinosaurs like Tyrannosaurus and Triceratops went extinct at the end of the Cretaceous, the little feathered ones flew on into history. More species are alive now than during Mesozoic times. They just have feathers, wings, beaks, and no teeth. We should remember the dinosaurs every spring when we see the first robin.
Planet of the Bugs: Evolution and the Rise of Insects Page 14