Your first decision, if you are going to write about beetles, is whether to tell the story of J.B.S. Haldane, the great British biologist. A Marxist and an atheist, Haldane was asked whether his studies of nature had given him any insight into the character of the Creator. “Yes,” said Haldane, “he had an inordinate fondess for beetles.”
Dr. Margaret Thayer, an adjunct curator at the Field Museum whose specialty is beetles, tells me that Haldane may not have said that great line. According to her, this story is endlessly current among students of beetles, but she has heard the line attributed to a number of eminent beetle authorities. Maybe Haldane said it once. Maybe when he said it he was quoting someone else.
The inspiration for Haldane–or the pseudo-Haldane–and the thing that keeps Margaret Thayer busy is the enormous variety of changes that have been rung on the basic beetle body plan. Beetles, with 300,000 species, represent about 25 to 30 percent of all known animal species–a number roughly equal to all the plant species ever described. God must love beetles even more than he loves poor people.
The basic plan of a beetle is a variation on the basic plan of insects: three body segments (head, thorax, abdomen), a pair of legs attached to each of the three thoracic sections, an exoskeleton that armors the bug against the world and also provides its muscles a place to attach.
Most beetles can fly, though they use only their hind wings for the job. Their forewings have been modified into hardened coverings called elytra, two half shells that meet down the center of the insect and shield the folded wings from damage.
A lot of beetles–ladybugs, for example–have a humpbacked look. On these insects the orange elytra with their black spots cover all the abdominal segments. Other beetles have more elongated bodies with short elytra. Abdominal segments extend well beyond the elytra in these insects.
Prominent in the elongated group is a family called the Staphylinidae, the rove beetles. Rove beetles are the largest family of North American beetles, with more than 3,000 species described so far. Along with a smaller group, the Silphidae, or carrion beetles, the rove beetles are the focus of a research project Margaret Thayer is conducting at Swallow Cliff Woods and Cap Sauers Holdings, two Cook County forest preserves in the Palos area.
Since early summer she has been trapping beetles at six locations in these two preserves. Three of her trap sites are on land slated for major ecological restoration, and the other three are on sites where no restoration work is planned. With this year’s data as a baseline, trapping in future years will record the effects restoration work has on beetle populations.
Thayer estimates that about 400 species of these two families live in the Chicago area, and she is expecting her sites at Swallow Cliff and Cap Sauers–the traps are all in mature oak woods–to yield a total of about 100 species. She has provisionally identified species collected prior to July 10 and found about 85 different types.
Some of these belong to a genus called Proteinus, which has never been described in the Chicago area before. Another may be a new species never before described anywhere. Certainly one of the attractions of studying beetles is the real possibility that you could discover an entirely unknown species in your backyard–even if you live in a heavily studied area like eastern North America.
I spent part of a morning not long ago in Thayer’s lab at the Field Museum getting a magnified look at part of her Palos collection. Some of the specimens were so tiny that without magnification I couldn’t even tell they were insects.
The defining characteristics of beetles–in addition to the elytra–are the pronotum, an enlarged thoracic segment just behind the head, and biting mouth parts. Beetles do their chewing outside the mouth, employing hooked mandibles and palps to poke and crush their food. Once they have reduced their comestibles to a soupy mass, they suck the liquid into their mouths.
The eating habits of beetles may not be the sort of thing you want to read about over lunch, but nature is like that. Consider the burying beetles, a subgroup of the carrion beetles that is well represented in Thayer’s collections from Palos. Burying beetles patrol the forest floor in search of dead animals. Species tend to specialize–some looking for dead mammals, some for dead snakes, etc. When a pair of burying beetles discover a suitable corpse, they bury it by digging earth from under the body and allowing the dead animal to sink into the resulting hole. Then they cover it up with loose dirt. Burying is very useful behavior, since a buried corpse is safe from flies, and flies are major competitors with carrion beetles in the disposal business.
Carrion beetles are among the many animals that depend upon windfalls. You don’t discover a squirrel carcass every day, so if you do get lucky you have to be ready to take maximum advantage of your find. For carrion beetles this means mating, closely followed by the laying of as many eggs as the corpse will support. A dead mouse will feed only a few young. Larger animals can support larger broods. The adults care for the young. They prepare the meat for the larvae by prechewing it. They also clean and groom the young, and the adults’ own diet–they eat maggots–protects the food supply from competition.
Rove beetles are an active bunch. Many of them are predators. Even the smallest of them, insects only about one millimeter long, may prey on springtails and other very small creatures. The larvae of many species are also predatory. However, there are carrion feeders in the group as well as vegetarians that feed on everything from flowers to rotting wood.
Rove beetles have a long, skinny look. With their flexible abdomens extending well beyond the elytra, you could almost take one for a tiny, aberrant scorpion. Rove beetles do not sting, but the tips of their tails are often equipped with scent glands that can release a foul odor that discourages predators.
Thayer uses three different types of traps to catch these beetles. One is a simple pitfall trap that captures unwary beetles running across the forest floor. Another consists of a fabric awning pulled taut above shallow pans of water. When flying beetles encounter an obstacle like the awning they tend to drop down to avoid it. If all goes well–for Thayer, not the beetle–the insect will drop into the water.
The third trap is a pitfall baited with octopus meat. This is the preferred viand for beetle trappers because it retains its moisture–and therefore its attractive odors–for up to two weeks. Other meats tend to dry out and lose their smell.
Supplementing these traps are collections taken from leaf litter and rotting logs. The beetle that may be new to science came from a leaf-litter sample. It belongs to a genus that is mostly tropical but is represented in the U.S. by specimens from South Carolina and Florida and by one recent find in southwestern Michigan.
If you were studying birds, or reptiles, or any other group of vertebrates in the Chicago region you would have a pretty clear idea of what you would find. You could have small surprises. Animals might show up in unexpected places or fail to show up where you expected them. But you probably wouldn’t find any species that hadn’t been recorded from this area before, and your chances of finding a species new to science would be about as good as your chances of winning the lottery.
With beetles your chances are very good. And after you find that new species, you have to set to work elucidating the details of its life history. These can be quite complex. Some beetles go through a whole sequence of larval stages. An animal may be a freely running type for part of the larval stage and a nearly immobile grub for another part. If you are a student of beetles you will always have work to do.
Beetles are also very important actors in virtually all terrestrial ecosystems. As predators, as feeders on plant tissues, as cleanup specialists, their cumulative impact is enormous.
The creation of Chicago Wilderness–a coalition of 34 organizations devoted to fostering, studying, and protecting the biodiversity of the Chicago region–is stimulating many research projects like Thayer’s. We know we have some very special things in this region, but our knowledge is very spotty. We know a lot about some groups of plants and animals, and we know a lot about a few well-studied sites. But our ignorance is vast. Projects like Margaret Thayer’s are letting a little light into some very dark places.