When I think of caves I think of bats. Being an entomologist, I also think of bat droppings and the many insects that feed upon the droppings (more properly termed guano) that accumulate in caves under the bats’ roosts. This guano provides a moist, constantly replenished source of repugnant sustenance in an otherwise rather barren environment. As might be expected, most cave insects are detritivores: scavengers feeding on decaying organic material brought into the cave from an outside source.
There are also a number of predators feeding on the other insects with which they share the cave. Certainly, because of the lack of light, there are no plants and thus, none of the multitude of above-ground insects that rely on plants or plant products for their livelihood. But maybe it’s not that simple?
I specialize in the taxonomy and biology of weevils, perhaps the most diverse family of living things, and a group almost wholly dependent on plants or plant products for food. There are around 60 000 formally named species of weevils throughout the world. In Europe, surprisingly, there are around two hundred or so weevil species that have been found only in caves.
These weevil species show all the traditional traits of cave-adaptation such as reduced pigmentation, reduced or absent eyes and long appendages. How is this possible? What do these cave-adapted (or troglobitic) weevils feed on?
Also, if there is a modest number of troglobitic weevils in Europe, why are there virtually no troglobitic weevils in North America? Despite there being thousands of caves, particularly in the southern United States, and a rich fauna of other beetles and insects associated with these caves, there are no weevils. Well, almost none.
Back in 2009, I was sent some specimens of a species of Lymantes from a cave that I thought at first was a species collected rather commonly in leaf litter (now named by me as Lymantes fowleri). I thought in this case that the leaf litter was likely collected from around the mouth of the cave. It wasn’t until I noticed that these new specimens entirely lacked eyes and when I dissected them and had differently shaped male genitalia and later found out that they were collected deeper in the cave, that I recognized them as a distinct species, which I named Lymantes nadineae. At that time this species was pronounced as “North America’s first and only troglobitic weevil”.
Since then, the lack of troglobitic weevils in North America and the question of what might troglobitic weevils feed on has puzzled me. Was the lack of weevils a matter of a lack of collecting? Or was it related perhaps to differences in the structure or history of the cave systems, perhaps allowing for the evolution of cave-adapted weevils in Europe, but not in North America?
Because almost all cave-adapted weevils have immature stages that very likely feed on plant roots, might the caves where they are found in Europe be shallow and more or less parallel with the ground surface, such that tree (or other plant) roots can penetrate the roof of the cave? These roots could be the plant material on which these troglobitic weevils develop. Maybe few North American caves fit this description? Or maybe it’s just that North Americans have not been looking hard enough for them? Well, the answer to this last question might be near.
While in Austin, Texas, a few years ago, I met with James Reddell, now retired, but one of the foremost cave naturalists in the United States. James passed along a few vials of weevils that he had accumulated over the course of his career. Included were some exciting finds, most notably a single specimen of an obviously troglobitic (and new to science) weevil from Spider Cave, a small cave within the Austin city limits.
James is now in the process of sending me additional specimens of this species, along with a variety of other weevils that he has accumulated that were collected “in caves”. I’ve not yet received the package, but perhaps the contents can help address the question that the lack of cave weevils is from to a lack of collecting. As this package from James represents the best efforts of cave biologists over the last 50 years, might there be other finds equivalent to the Spider Cave beast? I sure hope so.
Christmas passed by a few months ago, but for entomologists, exciting gifts can be had at any time of the year. I’ll keep you posted.