Iin our thirtieth-anniversary issue, we revisit endangered species.
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Our cover shows a Florida scrub millipede (Floridobolus penneri). When threatened, the millipede resorts to chemical warfare, secreting a distasteful defenseive cocktail. The secreted droplets can be clearly seen in this photograph by Thomas Eisner. |
Snapshots at the Edge of a Cliff Everywhere one might care to look in our human-conquered world one can find habitats in trouble. The insects, spiders, and other small creatures of these endangered habitats know nothing of their peril. They uphold their ancestral ways of life with no inkling that they are on the brink of the bottomless cliff of extinction. We have followed a few of these little crawling and hopping animals, hoping that we are not recording last moments. We hope that the information these animals have provided will make them interesting and give them individuality. We hope that the obvious potential for future revelations will make the preservation of these animals seem worthwhile. Then, we hope, the concept of guard rails to prevent species plunging over the cliff will spring to mind.
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The Lake Placid funnel wolf spider (Sossipus placidus) displays unusual behavior. Most wolf spiders, as their name implies, roam about the surface of the ground, pouncing on prey and subduing it with their large fangs. The funnel wolf spider, however, takes over a hole, such as an abandoned mouse burrow, and weaves a silk corridor leading up out of the hole and opening out onto a broad, flat sheet of silk spread across the leaves and twigs of a plant. In the vegetation above this sheet the spider spins a series of widely spaced lines that go this way and that. Flying or leaping insects hit these lines and tumble down to the trampoline of death below, where the spider comes rushing out to finish them off. The female spider is a particularly attentive mother, caring for her young until they are about half grown. Upon catching a large moth or grasshopper, she leaves it in the web for her young, which cluster around to feed. Eventually, responding to some unknown coming-of-age stimulus, the young spiders leave to set up their own establishments. |
| The rosemary grasshopper (Schistocercus ceratiola) is unusual among its kin for its dietary fussiness. The genus Schistocercus, which includes the notorious plague locust of Africa and the Middle East, is generally composed of hefty, voracious species that feed with undiscriminating gusto on the leaves of various trees and herbs. The rosemary grasshopper is a small, slender hopper that depends entirely on Florida scrub rosemary. Why should a species evolve such a dangerously specialized diet? One reason may be that it takes a specialist to deal efficiently with high levels of specific defensive chemicals in plants, and, from its distinctive and pungent odor, scrub rosemary is obviously loaded with volatile chemicals. While scrub rosemary may not be a dominant plant in the Florida landscape today, in its time, during dry periods of the Pleistocene, scrub rosemary apparently covered huge areas of the Florida peninsula. Back then, the rosemary grasshopper was sitting pretty, far from its present precarious perch. |  Feeding solely on Florida scrub rosemary (Ceratiola ericoides), the fate of the rosemary grasshopper (Schistocercus ceratiola) relies on the continued presence of its food plant in habitat that is facing ever-greater pressure for development. Photograph by Thomas Eisner. |
The Tequesta grasshopper (Melanoplus tequestae) is one of a number of small, flightless grasshoppers that have remarkably restricted ranges. In peninsular Florida there is a series of ancient sand ridges, derived from sediment washed down from the Appalachians and deposited on the limestone platform of Florida. Today these sand ridges form isolated uplands, whose rapid-draining soils support a desert-like community.
The Tequesta grasshopper is a species that is marooned on the
long, narrow Lake Wales Ridge and what is left of the Orlando and southern
Mount Dora Ridges. To the east is a ridge with the Atlantic coastal grasshopper;
to the northeast is a ridge with the Volusia grasshopper; to the north is
a pair of ridges, one with Nancy's grasshopper and the other with Ordway's
grasshopper. These grasshoppers are significant in that they tell us which
ridges have long been isolated from each other, even during dry periods of
the Pleistocene. The Volusia grasshopper, for example, should direct our attention
to the Deland-Crescent City Ridge, where we might find other isolated species
or distinctive populations of plants and animals. Nobody has gotten around
to following up on this particular grasshopper clue, but that is not the fault
of the grasshoppers.
Workman's jumping spider (Phidippus workmani) is a large and colorful
species known from only a few sites. It seems to be confined to Florida scrub
habitat; we do not know why it should require this habitat, since it seems
to be a general predator, attacking a variety of insects. In its dependence
on Florida scrub, Workman's jumping spider resembles the four other species
mentioned in this article.
Florida scrub habitat is a habitat in trouble because the sandy
uplands where it occurs never flood, unlike the lowlands that make up much
of Florida. This characteristic means that Florida scrub has been readily
converted to citrus groves or housing developments. To make matters worse,
different scrub "islands" have different species, so species conservation
would require a number of preserves.
The Florida scrub millipede (Floridobolus penneri) is a large burrowing
millipede, the color of an old gray filing cabinet crammed with odd facts.
This millipede (shown on the front cover) is the only representative of an
isolated lineage of uncertain origin; for a while it was even placed in its
own family, the Floridobolidae. Chemists at Cornell University have identified
the chemical defenses of the scrub millipede, finding six different quinones,
including a previously unknown compound. Do the millipedes really need such
a varied arsenal to repel insects and spiders, or is the variety a by-product
of the synthetic pathways churning away in the defensive glands? Certain flies
that parasitize millipedes seem to home in on the odor of defensive quinones.
Does this effect how and when millipedes deploy their chemicals? Scampering
about the millipedes' bodies are tiny mites, apparently restricted to this
species. We don't know what these mites do, but they remind us that even a
single species can support its own unexplored mini-community. Floridobolus
feeds on tough dead leaves of scrub oaks, an austere diet that probably requires
some (as yet unknown) digestive tricks.
Among the endangered arthropods, the most unusual thing about the five species
portrayed above is that we actually know of their existence, and even a little
about their biology. The rate of destruction and degradation of natural habitats
is currently so great that there are not nearly enough biologists to even
catalog the species that are suddenly on the edge of extinction. As invasive
exotic ants begin to roll across some Pacific island, as loggers eye the last
remnants of a cloud forest, as valleys are flooded, as savannahs become intensive
cattle ranches, as deserts are mined, as woodlands become tree farms, as whole
landscapes are, for one reason or another, subjected to aerial insecticides,
as small wars level the countryside, we are losing more than we can know.
In these ways we lose large numbers of species of small animals before they
can be recognized as endangered and before they can tell their stories.
The reverse, however, is also true. Whenever preserves of protected habitat are established, such as the numerous preserves set up in Florida in the last twenty years, we are saving much more than we can know. Sitting relaxed behind the guard rails of these preserves, we, and the naturalists that come after us, can conduct long, leisurely investigations of little animals with big stories. We can allow ourselves to be lured by tangents, to uncover obscure connections, to wander happily among strange concepts, and then, with a start, to suddenly realize that we have discovered something that we have always needed.
Mark Deyrup is a research biologist at the Archbold Biological
Station in central Florida. His special interests include arthropods of the
Florida scrub habitat, arthropod conservation, and ants of the southeastern
United Sates and West Indies. Thomas Eisner is the Schurman Professor of Biology
at Cornell University, director of the Cornell Institute for Research in Chemical
Ecology, and president of the Xerces Society. He has written extensively on
science, conservation, and natural history, and is also a widely published
nature photographer.
Other articles in this issue include:
- "Lessons from Two Endangered Invertebrates," by Michael J. Bean
- "White Abalone: The First Marine Invertebrate Protected Under the Endangered
Species Act," by Brendan Cummings.
- "Resurrection Ecology: Bring Back the Xerces Blue!" by Robert
Michael Pyle.
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