A Natural History of the Central Appalachians

Chapter 09: Non-Insect Arthropods and Other Invertebrates

CHAPTER 09 NON-INSECT ARTHROPODS AND OTHER INVERTEBRATES MORE THAN 95 PERCENT of all described species of animals are invertebrates (i.e., lacking an internal skeletal system), and members of this large and diverse assemblage are well represented in the Central Appalachians. Some of these, including the larger insects (e.g., butterflies), are conspicuous, but most invertebrates are smaller and often live in environments where they are likely to be overlooked. This is especially true of the numerous very small forms, which can be incredibly abundant and yet are unknown to most people. Although one typically thinks of terrestrial invertebrates as being smaller than vertebrates, in the Central Appalachians and elsewhere a few exceptionally large invertebrates (e.g., crayfish) are larger than the smallest vertebrates (e.g., minnows). Even the smaller invertebrates can make their presence known to humans as pests: some are familiar (e.g., mosquitoes, wasps, bees, chiggers, ticks, and leeches); others are less so but are nonetheless economically important (e.g., various intestinal parasites such as roundworms and tapeworms). Still other invertebrates (e.g., spiders) are not necessarily pests but are disliked by most people. ARTHROPODS Most of the invertebrates mentioned above are arthropods, an extraordinarily large group of organisms characterized by a segmented body (though this is not always obvious) with a hard outer covering (an exoskeleton) and jointed appendages. The arthropods include both insects—the largest group of terrestrial animals worldwide—and various groups of noninsect arthropods. In addition to the arthropods, representatives of numerous other groups of invertebrates are found in the Central Appalachians. Although many of these are small to very small, a few can reach a length of several inches. This chapter focuses on the non-insect arthropods and other invertebrates. Insects will be discussed in chapter 10. Several groups of non-insect arthropods are commonly encountered in nature. The most prominent examples are arachnids, crustaceans, centipedes, and millipedes. Both the arachnids and the crustaceans are abundant and play important ecological roles in nature, albeit in very different habitats. As a group, crustaceans are aquatic (freshwater and marine), while arachnids are terrestrial. The most familiar crustaceans are those that appear on restaurant menus—shrimp, lobster, and (to a lesser extent) crayfish. Numerous smaller forms are major food items in the diet of small fish in freshwater ponds and streams (e.g., various types of water fleas, with members of the genus Daphnia the best-known), and various free-swimming crustaceans in the oceans of the world, collectively referred to as krill, are thought to represent the greatest biomass of any group of animals on earth. The easiest way to observe some of the tiny crustaceans present in a freshwater pond, where they are especially abundant, is simply to collect a little water in a glass jar or similar container. Holding the jar up to the light and looking closely at the water inside will reveal tiny “particles” that appear to be moving up and down or back and forth. Most of these are tiny freshwater crustaceans. The crayfish (sometimes called crawfish or crawdad), a much larger crustacean, is a familiar inhabitant of bodies of water throughout the Central Appalachians. Mature adults in some species can reach a length of as much as six inches, often making it the largest aquatic animal in springs and small, headwater streams. Crayfish are nocturnal and seek shelter during the day under rocks and dead, submerged wood in the body of water in which they dwell. Although aquatic, crayfish sometimes venture out of the water for short periods during the night. They are commonly regarded as scavengers but will feed upon any small aquatic animals they can capture, as well as some living plant material. Anyone familiar with the lobster cannot fail to notice how similar it is in appearance to a crayfish. Not surprisingly, the two animals are closely related. The most frequently encountered terrestrial crustaceans are woodlice, although some species are more widely known as pillbugs or sowbugs (fig. 78). Woodlice are detritivores (“detritus feeders”), which is a term used to FIGURE 78 Pillbug, one of the most commonly encountered terrestrial crustaceans 149 09 NON-INSECT ARTHROPODS AND OTHER INVERTEBRATES ARACHNIDS AS ARTHROPODS The arachnids include spiders, and to some people the two terms are one and the same. Yet the arachnids include several other groups, the most common and widespread of which are mites, ticks, and harvestmen. Although this fact is not...