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As we wander and crawl through cave passages here in the West, on the ground we
often see small, compact, elongated pellets of about 1/2 inch long by 1/8 inch in
diameter. Most of us know that these are the droppings or dung of the packrat
(Neotoma spp.), which regularly lives and nests in caves. But how many of you have
ever seen these pellets where most are riddled with tiny holes? Could this be
the dung of introduced Swiss packrats? Do these particular packrats have gas?
As most of you who have visited this cave already know, Mitchell Caverns is really two caves: El Pakiva and Tecopa. In 1970, a tunnel was dug connecting these caves in order to facilitate tours. These endemic spider beetles were discovered during a preliminary biological survey of the caves in 1979.2 Despite the tunnel connecting the two caves, which by then had been in place for nine years, and despite the abundant packrat nests in both caves, these beetles were found only on the El Pakiva side. Furthermore, the deeper into El Pakiva Cave one looked, the more abundant the beetles became! In 1991, I was asked to re-study these beetles to provide baseline data that could be used in establishing management policies for the Caverns. During this 1991 study3, live traps were placed throughout Mitchell Caverns to determine the abundance of these beetles and other endemics. Specimens were counted from each trap and released. Surprisingly, even though by this time the two caves had been connected for 21 years, these beetles were still found only on the El Pakiva side and still were the most abundant in the deepest part of the cave.
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Holey Dung!
The answer is neither of these: the holes in the pellets have nothing to do
with the packrats. Rather, they are created by an unusual beetle’s immatures
(larvae) that feed on the dung. This tunneling coprophagy (dung feeding) habit
seems to be restricted to this type of spider beetle. The beetle lays its eggs
on the dung, and the larvae hatch and feed on it, making the tunnels. (Figure 1)
The adults probably feed on the dung as well, along with other organic material.
Although epigean (non cave-dwelling) species of these beetles are found throughout
the Western United States, cave endemics (species restricted to particular caves)
are known only from a few caves in California and Utah. If you are lucky enough
to actually spot one wandering around in a cave, you might think you have lost
your mind! The round yellow-orange adult beetles, about the size of a BB, look
much like a small walking cave pearl! Unlike their epigean relatives, (Figure 2)
these cave endemics have very reduced eyes as well as characteristics associated
with cave life. (Figures 3a and 3b)
Back in 1995, a colleague and I revised this genus of spider beetle (family
Ptinidae) of the genus Niptus1. One of the cave endemics we described, Niptus
arcanus, (Figure 4) is known only from Mitchell Caverns, San Bernardino County,
California. Mitchell Caverns Natural Preserve is part of the Providence Mountains
State Recreation Area.
So if next time you are crawling in a cave that you know has packrats, take
some time to look at these interesting pellets carefully for signs of burrowing.
If you find some, please drop us (the WCC) a note. Who knows? You may have
discovered a completely new species of Niptus. Holey dung! Can you see it now?
A scientific publication describing Niptus _______ (insert your name here): a
new species-with wonderful eating habits - named after you!