“If there is a Creator, he must have an inordinate fondness for beetles.” – JBS Haldane

This quote reflects the 400,000+ known species of beetles in the world, constituting almost 40% of all known insect species and 25% of all known animal life-forms. If there was a box filled with all the animals found on earth, on average every fourth time you reached in to pull one out it would be a beetle. Most insects have two pairs of wings (except the Diptera – flies – which have just one pair). Beetles have those two pairs of wings, except the forewings are modified not for flight, but to be a covering or sheath, protecting their body. In some beetle families, like the darkling beetles, the two halves of that protective sheath are fused, so they cannot fly. Carl Linnaeus named the Order for beetles as Coleoptera in the year 1758. Of the many families of beetles, weevils (Curculionidae) are the most speciose with over 80,000 species. Next are ground beetles (Carabidae) with 40,000 species, then scarab beetles (Scarabaeidae) with 35,000 species. The most common beetle family populating the deserts of the world are darkling beetles (Tenebrionidae) with some 30,000 species. To give that number some perspective, worldwide there are 11,000 species of birds, and just 7,000 species of lizards.

Around the world, wherever plants grow in profusion, there are organisms with the task of cleaning up those piles of leaves, along with those piles of dung left by animals eating those plants. If it wasn't so, we would all have to wade through miles-high piles of dead leaves, flowers, and woody debris every time we needed to move from here to there. In areas with ample rainfall, that task is largely accomplished by bacteria and fungi. Bacteria and fungi are neither plants nor animals, nor are they related to each other, but they are the most genetically diverse organisms on earth with an estimated millions of different taxa. Interestingly, we, along with all other animals, share more DNA with fungi than we do with bacteria or plants. In deserts it’s too dry to support many bacteria and fungi on the surface, although deeper in the ground amid the roots of creosote, mesquite, ironwoods, and paloverde fungi do play a critical role facilitating nutrient movement from the soil to the plants and sequestering carbon emitted by the plant’s roots. However, at the surface deserts are too hot and dry for these microorganisms to take on a major role in cleaning up the dead leaves and flowers left from the spring wildflower blooms. Yet, by fall there is often little or no evidence of those spring blooms. The clean-up crews are comprised of darkling beetles.

A term for of those pieces of dead leaves and flowers and dung is detritus, and tenebrionid (darkling) beetles are called detritivores, consumers of detritus. The profusion of darkling beetle species reflects the way that they have partitioned the desert detritus by time of year, size, and location. Back in 2000 I published a paper documenting the number of darkling beetles I had found just on the remnants of the Coachella Valley’s once vast sand dune system. I found 34 different species, including one previously un-named species. Some were as small as ants and apparently live inside harvester ant colonies, some were as big as my thumb. Some were only found on active dunes, others only on stabilized dunes. Some were only found on the cooler-wetter western sand fields and dune at the west end of the valley, some only at the hottest-driest eastern end of the dune system. Some only were found in the spring, others only in the fall. They have partitioned the dunes by space and time and partitioned the size of the detritus they eat and that might otherwise accumulate, occupying separate niches that allow the coexistence of so many species. Other darkling beetle species live on the desert’s rocky hillsides.

Years ago, I visited the sand dunes of the Namib Desert in southwestern Africa. There as many as 20 different darkling beetles live on those dunes. Unlike our desert, where rain is uncommon, it almost never rains on the Namibian dunes. Yet there are good numbers of lizards and beetles to be found there. Unlike our desert many mornings we awoke to dense fog, not rain but fog. Several of the darkling beetles adapted to this phenomenon by harvesting fog-water each morning. Some would excavate trenches at the top for the dunes and then collect fog droplets that accumulated along the edge of those trenches. Other beetles climbed to the top of the dune each morning and then stood motionless with their rear end pointed toward the sky. Fog would condense on their body and then drip down into their mouths.

Unfortunately, at some point people began the demeaning practice of calling these amazing darkling beetles “stink bugs” rather than acknowledging the critical ecosystem function that these beetles play. Clearly, they are beetles, not “bugs” and while some will emit a foul odor, it is only done when they are roughly mishandled and so aimed at protecting themselves from being eaten by a fox or coyote. I have handled countless darkling beetles and never once have been subjected to any unpleasant smells. Only one Order of insects, the Hemiptera, are classified as “bugs.” Sometime ago people got lazy and dismissively called anything with six or eight legs a “bug” rather than acknowledging the biodiversity found in the Phylum Arthropoda, Class Insecta or Arachnida, including spiders, scorpions, beetles, ants, bees, wasps, leaf hoppers, butterflies, moths, mayflies, or some other Order of arthropods. Hemiptera, the true bugs, like most insects, have two pairs of wings. However, as their name indicates, their forewing is only half (hemi) membranous and so built for flight, the other half being a thicker protective covering. Hemiptera typically have a hypodermic needle-like eating apparatus that they use for piercing plants to drink the fluids therein, or to pierce the skin of a vertebrate animal, and then drink their blood. Some true bugs do freely emit a most foul odor when threatened. Beetles are quite tame by comparison.

Nullius in verba

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