Insects and Spiders

Updated About encyclopedia.com content Print Article Share Article
views updated

Chapter 10
Insects and Spiders

Insects are members of the Animalia kingdom and belong to the phylum Arthropoda, along with crustaceans. There are many classes of arthropods, including the insects and arachnids. Both are invertebrates, but insects have six legs, while arachnids have eight legs. The arachnids include spiders, mites, ticks, scorpions, and harvestmen.

Insects are the most diverse group in the animal kingdom. Scientists are not certain of the total number of insect species; estimates range as high as thirty million species. Nearly one million of the species have been described. Insects have not been nearly as thoroughly studied as the vertebrate groups, and so there are likely to be many endangered insects whose desperate state is unknown.

Insects and arachnids, like numerous other species, suffer from diminished habitat as a result of encroaching development, industrialization, changing land use patterns, and invasive species.

THREATENED AND ENDANGERED INSECT SPECIES IN THE UNITED STATES

As of March 2006 there were forty-five U.S. insect species listed under the Endangered Species Act (ESA), as shown in Table 10.1. Predominant species types include butterflies (nineteen species) and beetles (eleven species). The remaining insects are an assortment of types including a dragonfly, a fly, a grasshopper, two ground beetles, two moths, a naucorid (which is pictured in Figure 10.1), three skippers, and four tiger beetles. Most of the listed insects are endangered, and nearly all have recovery plans in place.

According to the U.S. Fish and Wildlife Service (FWS) most of the imperiled insects are found exclusively in one of two states—California (twenty species) or Texas (seven species). The remainder of the species are scattered across the country.

The FWS reports that $7.5 million was spent under the Endangered Species Act during fiscal year 2004 on imperiled insects. The ten entities with the highest expenditures are shown in Table 10.2. Only three entities accounted for more than half of all money expended on insect species during that year. The Delhi sands flower-loving fly, which is pictured in Figure 10.2, and the valley elderberry longhorn beetle are both found in California. The Karner blue butterfly inhabits Midwestern states.

Butterflies, Skippers, and Moths

Butterflies, skippers, and moths are flying insects that belong to the order Lepidoptera. Scientists believe there could be several hundred thousand species in this order. Skippers have stockier bodies than butterflies, but are also structurally different from moths. They are considered intermediate between butterflies and moths.

Like amphibians, many butterflies and moths are considered indicator species (meaning that their wellbeing gives scientists a good indication of the general health of their habitat) because they are particularly sensitive to environmental degradation. The decline of these species serves as a warning to human beings about the condition of the environment. Part of the reason butterflies are sensitive to many aspects of the environment is that these species undergo a drastic metamorphosis, or change, from larva to adult as a natural part of their life cycles. Butterfly larvae are generally crawling, herbivorous caterpillars, whereas butterfly adults fly and are nectar-eating. Butterflies can thrive only when intact habitats are available for both caterpillars and adults. Consequently, healthy butterfly populations tend to occur in areas with healthy ecosystems. Because many species are extremely sensitive to changing environmental conditions, moths and butterflies are carefully monitored by scientists and conservationists around the world.

TABLE 10.1
Endangered and threatened insect species in the United States, March 2006
Common name Scientific name Listinga Recovery plan date Recovery plan statusb
aE=endangered; T=threatened.
bRecovery plan stages: U=under development, F=final, D=draft, and RF=final revision.
source: Adapted from "Listed FWS/Joint FWS and NMFS Species and Populations with Recovery Plans (Sorted by Listed Entity)" and "Listed U.S. Species by Taxonomic Group," in Threatened and Endangered Species System (TESS), U.S. Department of the Interior, U.S. Fish and Wildlife Service, March 6, 2006, http://ecos.fws.gov/tess_public/SpeciesRecovery.do?sort=1 and http://ecos.fws.gov/tess_public/SpeciesReport.do?kingdom=I&listingType=L (accessed March 6, 2006)
Beetle, American buryingNicrophorus americanusE9/27/1991F
Beetle, Coffin Cave moldBatrisodes texanusE8/25/1994F
Beetle, Comal Springs dryopidStygoparnus comalensisENone
Beetle, Comal Springs riffleHeterelmis comalensisENone
Beetle, delta green groundElaphrus viridisT3/7/2006F
Beetle, Helotes moldBatrisodes venyiviENone
Beetle, Hungerford's crawling waterBrychius hungerfordiE8/6/2004D
Beetle, Kretschmarr Cave moldTexamaurops reddelliE8/25/1994F
Beetle, Mount Hermon JunePolyphylla barbataE9/28/1998F
Beetle, Tooth Cave groundRhadine PersephoneE8/25/1994F
Beetle, valley elderberry longhornDesmocerus californicus dimorphusT6/28/1984F
Butterfly, bay checkerspotEuphydryas editha bayensisT9/30/1998F
Butterfly, Behren's silverspotSpeyeria zerene behrensiiE1/20/2004D
Butterfly, callippe silverspotSpeyeria callippe callippeENone
Butterfly, El Segundo blueEuphilotes battoides allyniE9/28/1998F
Butterfly, Fender's blueIcaricia icarioides fenderiE9/16/2005U
Butterfly, Karner blueLycaeides melissa samuelisE9/19/2003F
Butterfly, Lange's metalmarkApodemia mormo langeiE4/25/1984RF(1)
Butterfly, lotis blueLycaeides argyrognomon lotisE12/26/1985F
Butterfly, mission blueIcaricia icarioides missionensisE10/10/1984F
Butterfly, Mitchell's satyrNeonympha mitchellii mitchelliiE4/2/1998F
Butterfly, Myrtle's silverspotSpeyeria zerene myrtleaeE9/29/1998F
Butterfly, Oregon silverspotSpeyeria zerene hippolytaT8/22/2001RF(1)
Butterfly, Palos Verdes blueGlaucopsyche lygdamus palosverdesensisE1/19/1984F
Butterfly, Quino checkerspotEuphydryas editha quino=E.e. wrightiE9/17/2003F
Butterfly, Saint Francis' satyrNeonympha mitchellii francisciE4/23/1996F
Butterfly, San Bruno elfinCallophrys mossii bayensisE10/10/1984F
Butterfly, Schaus swallowtailHeraclides aristodemus ponceanusE5/18/1999F
Butterfly, Smith's blueEuphilotes enoptes smithiE11/9/1984F
Butterfly, Uncompahgre fritillaryBoloria acrocnemaE3/17/1994F
Dragonfly, Hine's emeraldSomatochlora hineanaE9/27/2001F
Fly, Delhi Sands flower-lovingRhaphiomidas terminatus abdominalisE9/14/1997F
Grasshopper, Zayante band-wingedTrimerotropis infantilisE9/28/1998F
Ground beetle, [unnamed]Rhadine exilisENone
Ground beetle, [unnamed]Rhadine infernalisENone
Moth, Blackburn's sphinxManduca blackburniE9/28/2005F
Moth, Kern primrose sphinxEuproserpinus euterpeT2/8/1984F
Naucorid, Ash MeadowsAmbrysus amargosusT9/28/1990F
Skipper, Carson wanderingPseudocopaeodes eunus obscurusE3/2/2006D
Skipper, Laguna MountainsPyrgus ruralis lagunaeENone
Skipper, Pawnee montaneHesperia leonardus montanaT9/21/1998F
Tiger beetle, northeastern beachCicindela dorsalis dorsalisT9/29/1994F
Tiger beetle, OhloneCicindela ohloneENone
Tiger beetle, PuritanCicindela puritanaT9/29/1993F
Tiger beetle, Salt CreekCicindela nevadica lincolnianaENone

Butterflies and moths have alerted scientists to numerous habitat changes. In southern Florida, for example, the sharp decline of swallowtail butterflies alerted biologists to the harm caused by mosquito sprays, as well as to the fact that pesticides had contaminated the water. In 1996 scientists in Michigan and England reported that during the 1960s darker-colored moths began to predominate over light, white-and-black-flecked moths in polluted areas (B. S. Grant and others, "Parallel Rise and Fall of Melanic Peppered Moths in America and Britain," Journal of Heredity, September/October 1996). This was seen in both England and the United States and was probably due to the fact that darker moths were better able to blend into the dingy environment and hide from predators. In both countries, clean air laws were passed and decreases in pollution resulted. Now, in both countries, lighter-colored moths are again predominant. Dr. Douglas Futuyma, a biologist at the State University of New York at Stony Brook, reported that other insect species have shown increases in the proportion of darker-colored individuals in industrialized areas, a phenomenon called "industrial melanism" (Carol Kaesuk Yoon, "Parallel Plots in Classic of Evolution,

TABLE 10.2
The ten listed entities with the highest expenditures under the Endangered Species Act, fiscal year 2004
Ranking Common name Listing* Expenditure
*E=endangered; T=threatened.
source: Adapted from "Table 1. Reported FY 2004 Expenditures for Endangered and Threatened Species, Not Including Land Acquisition Costs," in Federal and State Endangered and Threatened Species Expenditures: Fiscal Year 2004, U.S. Department of the Interior, U.S. Fish and Wildlife Service, January 2005, http://www.fws.gov/endangered/expenditures/reports/FWS%20Endangered%20Species%202004%20Expenditures%20Report.pdf (accessed February 11, 2006)
1Delhi Sands flower-loving flyE$1,673,466
2Valley elderberry longhorn beetleT$1,513,233
3Karner blue butterflyE$1,085,869
4American burying beetleE$448,459
5Saint Francis' satyr butterflyE$405,700
6Mission blue butterflyE$347,222
7Hine's emerald dragonflyE$312,170
8Quino checkerspot butterflyE$251,444
9Fender's blue butterflyE$248,155
1Oregon silverspot butterflyT$174,682

In many cases butterflies also help conservationists decide where to locate parks and nature refuges. Generally, the more varieties of butterflies that exist in an area, the more species of other animals and plants and plants will live there too. Unfortunately, many butterfly species are disappearing around the world.

The major threats to butterflies include:

  • Habitat destruction
  • Mowing of pastures, ditches, and highway rights-of-way
  • Collisions with moving automobiles
  • Insecticides

New York Times, November 12, 1996). In those species, as well, the proportion of dark specimens drops as air quality improves.

KARNER BLUE BUTTERFLY

The Karner blue butterfly was listed as endangered in 1992. Historically it occupied habitats in the eastern United States from Minnesota to Maine as well as Ontario, Canada. However, the species now is found only in portions of Minnesota, Wisconsin, Indiana, Michigan, New York, New Hampshire, and Ohio. Most Karner blue butterfly populations are very small and in danger of extinction.

The caterpillars of the Karner blue butterfly rely for food on a species of lupine that is now found primarily on roadsides, military bases, and some forest areas. The primary reason for endangerment of the Karner blue butterfly is habitat loss due to land development for human use and forest maturation. The U.S. Fish and Wildlife Service published a recovery plan for the species (http://www.fws.gov/midwest/Endangered/insects/kbb/recplan-fnl-nrel.html) in September 2003. Figure 10.3 shows the recovery units, or populations, of the species, sites for potential recovery units, as well as other sites where the species has historically been found.

BLACKBURN'S SPHINX MOTH

Blackburn's sphinx moth was first listed as an endangered species in February 2000 and is found exclusively in Hawaii. This moth species is threatened by urban development, conversion of land for agricultural use, invasive plant species, trampling of vegetation by nonnative ungulates (hoofed animals), and invasive predators and parasites.

Conservation recommendations in the species recovery plan, which was drawn up by the U.S. Fish and Wildlife Service in October 2003, include habitat conservation and restoration, planting of the moth's host plant in new habitats, and a captive breeding and reintroduction program. The total cost for recovery of the species is estimated at $5.5 million.

Santa Cruz Mountain Insects

California's Santa Cruz Mountains are home to two endangered species"the Zayante band-winged grasshopper and the Ohlone tiger beetle. Factors leading to endangerment include sand mining, urban development, conversion of land to agricultural uses, recreational use (such as hiking, horseback riding, off-road vehicle use, bicycling, and camping), competition with nonnative species, fire suppression, pesticides, logging, and over-collection.

ZAYANTE BAND-WINGED GRASSHOPPER

The tiny Zayante band-winged grasshopper, barely half an inch long, occupies areas containing abundant high-quality silica sand, known as Zayante or Santa Margarita sand. This sand is valuable for making glass and fiberglass products, and several businesses have entered the area in the hope of capitalizing on this. The Zayante bandwinged grasshopper joined the ranks of listed endangered species in January 1997. In 2001, as a result of a lawsuit filed by the Center for Biological Diversity, the FWS designated more than 10,000 acres of critical habitat for the grasshopper.

OHLONE TIGER BEETLE

The Ohlone tiger beetle was listed as endangered in October 2001. The species was discovered in 1987 and is found only in Santa Cruz County, California. The Ohlone tiger beetle is a small species, about half an inch long, with spotted metallicgreen wings and copper-green legs. Both adults and larvae hunt invertebrate prey. The Ohlone tiger beetle occupies a total of less than twenty acres of remnant native coastal prairie habitat on state land, private land, and property belonging to the University of California at Santa Cruz. The species declined due to habitat loss and habitat fragmentation resulting from urban development, as well as over-collection, pollution from pesticides, and the increasing encroachment of invasive plant species. The petition to list the Ohlone tiger beetle with the FWS was originally made by a private citizen in 1997.

Hine's Emerald Dragonfly

The Hine's emerald dragonfly has been listed as an endangered species since 1995 and is found in federal and state preserves and national forest lands in Illinois, Wisconsin, Michigan, and Missouri. In earlier times, its range extended through portions of Ohio, Alabama, and Indiana as well. The Hine's emerald dragonfly has a metallic-green body and emerald-green eyes. It is considered a biological indicator species because it is extremely sensitive to water pollution. The decline of this dragonfly species has resulted primarily from loss of suitable wetland habitat, such as wet prairies, marshes, sedge meadows, and fens (a type of bog) occurring over dolomite rock. (The lakeside daisy is another species damaged by the decline of these habitats and is listed as threatened.)

Wetland habitats support dragonflies during their aquatic larval period, which lasts some three to four years. Adult dragonflies occupy open areas and forest edges near wetland habitats, where they feed on invertebrate species such as mosquitoes. Hine's emerald dragonflies also serve as prey for a variety of bird and fish species. The recovery plan for the dragonfly includes measures to protect current habitat as well as reintroduction of the species to portions of its former range. Private companies that own land supporting dragonfly populations have aided conservation efforts by monitoring populations and preserving important habitat areas.

THREATENED AND ENDANGERED FOREIGN SPECIES OF INSECTS

As of March 2006 there were only four foreign insects listed under the Endangered Species Act, as follows:

  • Luzon peacock swallowtail butterfly (Papilio chikae)
  • Homerus swallowtail butterfly (Papilio homerus)
  • Corsican swallowtail butterfly (Papilio hospiton)
  • Queen Alexandra's birdwing butterfly (Troides alexandrae)

All four butterfly species have endangered status.

The World Conservation Union (IUCN) listed 559 species of insects as threatened in its 2004 Red List of Threatened Species. This number comprises nearly three-fourths of the species evaluated, but less than 1% of described species.

Monarch Butterfly

Among the best-known insect species, the adult monarch butterfly is characterized by orange wings with black veins and white spots at the outer margins. Historically, monarch butterflies migrated by the millions up and down the North American continent on a journey extending 3,000 miles. Over time, monarch butterfly populations have also become established in Australia and on the Pacific islands of Samoa and Tahiti. Other monarch populations have appeared in Hawaii and New Zealand.

For many years, naturalists sought to pinpoint the location where monarchs hibernate in January and February in preparation for their mating season and northward migration in March. In 1975, following an arduous search, a serene monarch hibernation area was located in the high altitude forests of the Michoacán Mountains in Mexico. Mexico declared the impoverished region a protected area. The inhabitants of the area turned the site into an ecotourism attraction in order to generate income for the economy. However, ecotourism not only failed to generate sufficient money to support the people of the area, but also caused severe habitat disruption. The onslaught of tourists affected habitats by introducing excessive noise, tobacco smoke, fire, and pollution. Monarch butterflies are now considered endangered by the IUCN. The FWS and the Mexican government have since attempted to nurture a self-sustaining economy in the monarch hibernation area by introducing fish breeding and horticulture.

THREATENED AND ENDANGERED ARACHNID SPECIES IN THE UNITED STATES

As of March 2006 there were twelve U.S. species of arachnids listed under the ESA, as shown in Table 10.3. All of the arachnids have endangered status, and six of them have recovery plans in place. The imperiled arachnids fall into four species types, as follows:

  • Harvestmen—three species
  • Meshweaver—four species
  • Pseudoscorpion—one species
  • Spider—four species

Ten of the arachnids are cave-dwelling species found only in Texas. The only imperiled arachnids outside of Texas are the Kauai cave wolf spider, which inhabits Hawaii, and the spruce-fir moss spider, which is found in North Carolina and Tennessee.

Table 10.3 also lists the expenditures made under the Endangered Species Act for arachnid species during fiscal year 2004. In total, $1.55 million was spent. The Bone Cave harvestman, a Texas species, accounted for $1.36 million of this total.

Texas Cave Arachnids

Ten of the listed arachnids are found only in underground karst caves in a handful of counties in Texas. (See Figure 10.4.) Karst is a geological term referring to a type of underground terrain resulting when limestone bedrock is exposed to mildly acidic groundwater over a long period of time. Eventually the bedrock becomes a honeycomb of cracks, fissures, holes, and other openings. There are dozens of these karst caves located in Bexar, Travis, and Williamson counties in Texas. In recent decades scientists have discovered unusual invertebrate species living in these caves. The tiny cave dwellers are eyeless and have no pigment (color) to their bodies. Ten of the creatures have been added to the endangered species list. They include two true spiders, one pseudo-scorpion, four meshweavers (tiny web-making arachnids), and three harvestmen (commonly known as "daddy longlegs" or "granddaddy longlegs").

The species were listed under the Endangered Species Act after a collection of conservation groups petitioned the U.S. Fish and Wildlife Service in 1992. The creatures were listed as endangered in 2000. In 2003 approximately 1,000 acres were designated as critical habitat for six of the arachnids. In addition, four of the species are included in a recovery plan published in 1994 that also covers other imperiled invertebrate species living in the caves.

TABLE 10.3
Endangered and threatened arachnid species in the United States, March 2006 and expenditures for them in fiscal year 2004
Common name Scientific name Lisinga Recovery Plan date Recovery plan statusb Expenditures under ESA in fiscal year 2004
aE=endangered.
bRecovery plan stages: F=final and D=draft.
source: Adapted from "Listed FWS/Joint FWS and NMFS Species and Populations with Recovery Plans (Sorted by Listed Entity)" and "Listed U.S. Species by Taxonomic Group," in Threatened and Endangered Species System (TESS), U.S. Department of the Interior, U.S. Fish and Wildlife Service, March 6, 2006, http://ecos.fws.gov/tess_public/SpeciesRecovery.do?sort=1 and http://ecos.fws.gov/tess_public/SpeciesReport.do?kingdom=I&listingType=L (accessed March 6, 2006), and adapted from "Table 1. Reported FY 2004 Expenditures for Endangered and Threatened Species, Not Including Land Acquisition Costs," in Federal and State Endangered and Threatened Species Expenditures: Fiscal Year 2004, U.S. Department of the Interior, U.S. Fish and Wildlife Service, January 2005, http://www.fws.gov/endangered/expenditures/reports/FWS%20Endangered%20Species%202004%20Expenditures%20Report.pdf (accessed February 11, 2006)
Harvestman, Bee Creek CaveTexella reddelliE8/25/94F$7,140
Harvestman, Bone CaveTexella reyesiE8/25/94F$1,361,780
Harvestman, Cokendolpher CaveTexella cokendolpheriENone$10,000
Meshweaver, Braken Bat CaveCicurina veniiENone$10,160
Meshweaver, Government Canyon Bat CaveCicurina vesperaENone$10,160
Meshweaver, Madla's CaveCicurina madlaENone60,160
Meshweaver, Robber Baron CaveCicurina baroniaENone$10,160
Pseudoscorpion, Tooth CaveTartarocreagris texanaE8/25/94F$8,660
Spider, Government Canyon Bat CaveNeoleptoneta micropsENone$10,160
Spider, Kauai cave wolf or pe'e pe'e maka 'oleAdelocosa anopsE2/9/05D$32,101
Spider, spruce-fir mossMicrohexura montivagaE9/11/98F$13,500
Spider, Tooth CaveLeptoneta myopicaE8/25/94F$11,320

Kauai Cave Wolf Spider

The Kauai cave wolf spider, ranging from about one-half to three-quarters of an inch in length, is a blind species found only in special caves on the southern part of the island of Kauai in Hawaii. These caves are formed by young lava flows. Unlike most other spiders, which trap their prey in webs, the Kauai cave wolf spider hunts its prey directly. Its prey includes the Kauai cave amphipod, a species that is also highly endangered. The FWS originally listed both species as endangered in January 2000. Female cave wolf spiders lay some fifteen to thirty eggs per clutch, and carry young on their backs after hatching. Cave species are extremely sensitive to changes in temperature and light. In 2005 the Fish and Wildlife Service published a draft recovery plan covering both imperiled invertebrates living in the Kauai cave. The critical habitat established for the species includes fourteen units totaling 272 acres on the southern part of the island.

Spruce-fir Moss Spider

The spruce-fir moss spider is an endangered spider related to the tarantula. It was placed on the Endangered Species List in 1995. Spruce-fir moss spiders live in moss mats found only in the vicinity of Fraser fir trees. Its populations have declined largely due to the introduction in the United States of an invasive European insect species, the balsam-woolly adelgid. The balsam-woolly adelgid infests Fraser fir trees, causing them to die within a time period of two to seven years. With the death of numerous fir trees, other forest trees have also blown over. The resulting increase in light level and temperature causes the moss mats on the forest floor to dry up.

In 2001 the U.S. Fish and Wildlife Service designated critical habitat for the species, including areas in the Great Smoky Mountains National Park and the Pisgah and Cherokee National Forests, as well as a preserve managed by the Nature Conservancy. This designation of critical habitat followed a lawsuit against the agency, which had previously deemed designating critical habitat "not prudent" because it believed the spider would be more vulnerable to collectors.