ENDANGERED TERRESTRIAL INVERTEBRATES Mark Deyrup Archbold Biological Station I. Evidence of Multitudes of Endangered Terrestrial entire lives (e.g., spiders) as opposed to animals that Invertebrates live in water for their entire lives (e.g., lobsters). II. Awareness and Understanding of Endangered Ter- There are also many amphibious animals that spend restrial Invertebrates part of their lives in both places (e.g., dragonflies). III. The Special Perils of Specialists terrestrial invertebrates Animals that are not verte- IV. The Significance of Endangered Terrestrial Inver- brates (such as fish, reptiles, amphibians, birds, and tebrates mammals) that live on land for their entire lives. V. No Second Chances Examples are all insects except for those with aquatic larvae; nonaquatic mites and nematodes; and all spi- ders, millipedes, centipedes, and scorpions. GLOSSARY alien invertebrates Invertebrates intentionally or acci- dentally imported by humans into new geographic SIMPLE STATEMENTS CAN RAISE the most compli- areas. cated questions. There are two simple facts about en- coevolution Long-term evolutionary adaptation of spe- dangered terrestrial invertebrates. The first is that there cies to each other (e.g., mutually beneficial relation- are great numbers of these endangered animals—many ships between bees and flowering plants). thousands of species. The second is that nobody knows endangered species Species that are likely to become enough to make a comprehensive list of these species. extinct in the near future because of normal human Without such a list, how is it possible to say whether activities. Examples of such activities are land clear- this list would be long or short and whether it would ing for agriculture or housing and accidental impor- really contain many thousands of species? What is the tation of invasive species through commerce. evidence that there are huge numbers of endangered endemic species Species confined to areas where they terrestrial invertebrates that are missing from lists of evolved (e.g., flightless crickets in the Hawaiian endangered species? Why aren’t biologists moving more Islands). quickly to add the missing names to the list? Are terres- habitat specialists Species found only in a specific hab- trial invertebrates particularly vulnerable to ongoing itat (e.g., species found only in forests of Sequoia rapid changes caused by our own species? If there are trees). such large numbers, what does this mean for the forests, terrestrial animals Animals that live on land for their fields, deserts, and other habitats that are threatened Encyclopedia of Biodiversity, Volume 2 Copyright 2001 by Academic Press. All rights of reproduction in any form reserved. 487 488 ENDANGERED TERRESTRIAL INVERTEBRATES with the loss of these species? What does it mean for our own species? I. EVIDENCE OF MULTITUDES OF ENDANGERED TERRESTRIAL INVERTEBRATES The belief that there are very large numbers of endan- FIGURE 1 The Hawaiian tree snail Achatinella mustelina is1of41 gered terrestrial invertebrates is based on a combination species in its genus; 22 of these species are extinct, and the remaining 19 are severely threatened. These elegant, specialized, and slow- of knowledge and logic. The great majority of all ani- growing snails have been clobbered by a series of disasters. There mals are terrestrial invertebrates, in which are included was a shell-collecting frenzy of the 1800s, which also decimated at least three-fourths of the insects, most mites, terres- populations of Florida tree snails. This was followed by the destruc- trial mollusks, a large percentage of the nematodes, and tion of most of the forest habitat in which Achatinella species live. all the spiders, millipedes, and centipedes. The last three Finally, in 1955, a predatory snail species was introduced to combat an introduced species of African snail that is destructive to Hawaiian groups total more than all the vertebrates. If the factors agriculture. The killer snail quickly eliminated several species of that endanger other animals also affect terrestrial inver- Achatinella, and several other species survive only as captive colonies. tebrates, the number of endangered terrestrial inverte- brates must be large indeed. These factors are primarily habitat destruction and the introduction of nonnative species into new areas, and it is known that they affect A. Logistical Problems terrestrial invertebrates. A major logistical problem is an insufficiency of experts. Hawaii, showcase of beleaguered biota, is a revealing There are so many species of terrestrial invertebrates example of these factors at work on terrestrial inverte- that it is easy to find groups with hundreds or thousands brates. Of the total number of animals that live on the of species that can only be identified by two or three Hawaiian Islands and in the surrounding sea, about people. Who can identify the dark-winged fungus gnats, three-fourths are terrestrial invertebrates, 99% of which Indonesian bark beetles, the egg parasites of tropical are found only on the Hawaiian Islands. The islands are sac spiders, the mites associated with millipedes, or any so strongly affected by habitat destruction that whole one of innumerable large groups of small organisms? habitat types, containing all their habitat-specific inver- The few people who do study these groups are generally tebrates, are considered endangered. Invasions of alien overwhelmed with species that are undescribed and plants and animals are so severe that whole groups of with species whose biology is almost completely un- invertebrates have been devastated, such as the Hawai- known. Recognizing any of these species as endangered ian land snails, which were originally believed to num- requires documentation of distribution and abun- ber approximately 1000 species but now number ap- dance—levels of information that will probably not be proximately 500, with most of the remaining species available for most terrestrial invertebrates for approxi- endangered. The Hawaiian Islands may provide the best mately another century (Fig. 2). opportunity to document relatively easily the scale of A second logistical problem is that specialized the threat to terrestrial invertebrates in especially vul- knowledge is needed not only for identifying most ter- nerable places, such as oceanic islands (Fig. 1). restrial invertebrates but also for finding and counting them. Species that are rare in museum collections are not necessarily rare in nature; they are frequently spe- II. AWARENESS AND cies that are difficult to find because their habits are unknown. Certain flightless pygmy mole crickets, for UNDERSTANDING OF ENDANGERED example, are very common in ancient dune areas in TERRESTRIAL INVERTEBRATES Florida, but until recently there were no specimens in museums because nobody knew to look for these insects Why is it taking so long to recognize and document just under the surface of the sand just after a heavy rain. endangered terrestrial invertebrates? There seem to be Many grasshoppers have species-specific songs which both logistical and strategic considerations involved. biologists must learn to study the abundance of the ENDANGERED TERRESTRIAL INVERTEBRATES 489 FIGURE 2 With regard to terrestrial invertebrates, there may be few people with the specialized knowledge to identify even large and easily characterized species. Many species could become rare or ex- tinct without triggering alarms. The giant lacewing, Polystoechotes punctatus, apparently a common and widespread insect a century ago, is now so rare that few entomologists have seen a living individual. Nobody is writing distraught letters asking about the disappearance of this animal, and it does not appear on any list of endangered species. Nobody is doing any methodical surveys for this species; nobody knows how one would go about making such a survey because the ecology of the insect is poorly known. This species, which is relatively large (7-cm wingspread), distinctive, and of special interest because it is so primitive, has gone unrecognized as an endangered species. The great number of smaller and less conspicuous inverte- brate species have that have become rare or extinct have even less of a chance of attracting attention. adult insects; this has recently become a tool for study- ing endangered grasshoppers. Estimating the abun- dance of a species also requires specific knowledge of FIGURE 3 The red widow spider (Latrodectus bishoppi) is rare in life cycles and population dynamics. Many terrestrial the sense that it has a very small geographic range (a few areas of the invertebrates have a dormant period in the egg or pupal Florida peninsula) and a strict habitat requirement (Florida scrub). stage, during which they are almost impossible to find. Within its remnant patches of habitat, the red widow is sometimes Invertebrates often produce large numbers of offspring very common, whereas at other times it is extremely rare. This is probably due to predation by natural enemies such as spider wasps per female, and the percentage of survival of these off- and egg sac parasites. If one took a single survey in an area, one might spring may be strongly dependent on variable factors, conclude that this species was endangered or not at all endangered, such as weather or the population levels of certain pred- depending on the population level at the time of the survey. Is this ators. This means that populations may go through species endangered? Nobody knows. It depends on whether there frequent fluctuations