“If a god or divine being had created all living organisms on Earth, then that creator must have an inordinate fondness for beetles.” — J.B.S. Haldane

By DR. CAMERON BARROWS

The context for this quote was at a meeting attended by a diverse array of intellectuals. J.B.S. Haldane, a British geneticist and evolutionary biologist, found himself seated next to an archbishop, one of the top theologians of England’s Anglican church. The archbishop turned to Haldane and asked, After such a long career studying nature, what insights had he learned about the creations of God? Apparently without any hesitation Haldane delivered this reply.

Haldane was well aware that of all the animals known to exist on earth, beetles outnumber any other taxonomic group, by far. More than 400,000 species of beetles have been described, a number that is growing every year. That’s 40 percent of all insects. Compare that to birds (somewhat more than 11,000 species), lizards (at least 7,000 species) or mammals (just 6,400 species). Within the Order we know as beetles (Coleoptera), the three most species-diverse families include darkling beetles (Tenebrionidae – more than 20,000 species), scarabs (Scarabaeidae – more than 30,000 species), and weevils (Curculionidae – 83,000 species).

Although rare or uncommon in terrestrial habitats that have damp soils, throughout the warm desert regions of Earth, darkling beetles (Tenebrionidae or “Tenebs”) are especially abundant and they play a vital ecosystem role. We all have seen them, mostly nocturnal or active in the early morning hours, usually black in color. Often referred to as “stink bugs,” although more accurately called “stink beetles.” Some do emit an odor when disturbed, but most don’t. One, commonly referred to as the “Pinacate beetle” will do a headstand, challenging whoever is threatening it with an odiferous spray. Still, I have picked up many a Pinacate beetle and never been sprayed, making me think they are more often bluffing than offering any real threat.

Within deserts, darkling beetle species richness appears to be highest within the driest, most open desert expanses – sand dunes. Dr. Mary Seely found more than two dozen species of Tenebs occupying a sand dune system in one of the oldest deserts on earth, the Namib, located in southwestern Africa. The western portion of the Namib Desert abuts the southern Atlantic Ocean, and is what is called a “fog desert,” a region that rarely receives measurable rain but can regularly be blanketed by fog during the night and early morning. The fog forms when the cold moist air associated with the Benguela Current meets the warmer desert air. A handful of the darkling beetle species living within the “fog belt” have developed unique behaviors designed to harvest water from the fog. Some do what is essentially a Pinacate beetle headstand at the dune crests. The fog condenses on their abdomens and then drips down their bodies right into their mouth. Others construct trenches along the dune crests and then harvest water that condenses along the edges of the trench. These beetles, now sated with water, can then move that water through the food web by becoming prey of the ground-dwelling Namaqua chameleon, or other beetle-eating predators.

I found 34 species of Tenebs occupying the Coachella Valley’s remaining sand dune fragments, with individual dune fragments ranging from 9 to 29 species. To put that into perspective, think of an isolated grassland area with 34 species of antelope grazing on it, or a lake with 34 species of fish in it or 34 species of ducks dabbling across its surface. Thirty-four species of any single family occupying a discrete area is an amazing phenomenon. How do so many species divide up the precious little resources to be found on a sand dune?  Some select different microhabitats. One, the smooth death-feigning beetle, Asbolus laevis, is only found on active dunes, whereas its close cousin, the rough death-feigning beetle, A. verrucosus, likes more stabilized sand fields. It is not a fog desert so the beetles probably acquire water by burrowing down to water-saturated sands deeper in the dune. Or perhaps they can, like kangaroo rats and pocket mice, extract water through the metabolic break-down of the carbohydrate-laden food they consume. The Teneb species occurring on the Coachella Valley sand dunes range in size from not much bigger than the head of a pin, to some approaching two inches in length. Those size differences almost certainly parallel the size of food items they select, providing yet another means of dividing the finite food resource “pie.”

In terrestrial habitats with damp or wet soils (think tropical or eastern deciduous forests) a vital ecosystem process of breaking down dead leaves, twigs, branches, logs, as well as deceased animals, is accomplished by fungi and bacteria. The by-products of that decomposition are nutrients that then allow the forests and forest inhabitants to thrive. Darkling beetles typically don’t live in such habitats. In deserts, the hyper-arid conditions in the top layers of soil are usually not conducive for thriving bacteria and fungi. Here, in deserts, is where darkling beetles take on the critical role of being the primary decomposers, consuming and converting dead organic material into soil nutrients via their feces. The technical term for those who eat long-dead organic material is a detritivore, detritus being that long-dead organic material. Other organisms might eat live or fresh plants – vegetarians, or eat insects – insectivores, or eat freshly killed animals – carnivores. Detritivores have a key ecosystem function of converting long-dead detritus into soil nutrients, as well as keeping the habitats from accumulating ever-growing piles of dead vegetation. In deserts that key role is filled by sometimes dozens of Tenebrionid beetle species and their larvae.

The abundance of beetle species across our planet is a reflection of their “inordinate” ability to adapt and partition available resources across the diverse climates and habitats the earth provides. Our “fondness” for beetles could include appreciating that ability, and appreciating the ecosystem services they can provide.

Nullius in verba

Go outside, tip your hat to a chuckwalla (and a cactus), think like a mountain, and be safe.