Endangered Species Handbook

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It's Too Late

Invertebrates

     Invertebrates are key members of many ecosystems. Insects pollinate plants, while mollusks and gastropods form the basis of many aquatic food chains.  Documentation of invertebrate extinctions is incomplete, but a minimum of 375 species (approximately eight crustaceans, 72 insects, 31 bivalves and 260 gastropods, snails and related species) have become extinct worldwide in the past few hundred years, according to the 2000 IUCN Red List of Threatened Species (Hilton-Taylor 2000).  Massive destruction of many habitats, especially islands with endemic species such as land snails, has eliminated hundreds of these creatures.
 
     Extinct bivalves include mollusks native to the southeastern United States, the world's center of diversity for freshwater mussels.  Dam construction turned clear, fast-flowing rivers into still ponds, destroying prime mussel habitat.  Channelization, in which the natural curves of a river are straightened and its surrounding vegetation bulldozed from its banks, wreaked havoc in aquatic ecosystems.  Biologically rich rivers became muddy, sterile ditches.  These government-sponsored anti-flood programs took place during the first half of the 20th century, causing numerous extinctions of mussels and crayfish. 
 
     At the time, few people lamented the disappearance of these mussels, some of which were the size of dinner plates.  They grew in huge masses on river bottoms, serving as keystone species in river ecosystems by providing habitats for fish, crayfish and huge river snails.  Birds and aquatic mammals fed on the fish and other aquatic wildlife produced by these mussels; these large bivalves also cleansed the water with their filtering gills.  Water pollution from industry and coal mining and sedimentation from logging have contributed to their extinction.  Additionally, mussels are over-harvested because of their commercial value in the cultured pearl industry ‒ their shells are harvested and broken into tiny pieces that are inserted into living oysters to stimulate the growth of pearls.  These combined threats have pushed many species to extinction and others to endangered status.  Their demise has caused species dependent on mussels for reproduction and habitat to disappear as well.
 
     Scores of colorful endemic land snail species have died out in the Hawaiian Islands, other Polynesian and Indian Ocean islands and various southern Atlantic Ocean islands.  These snails were once prolific in native forests, but naturalists and shell collectors took many thousands of them during the 19th century ‒ until the 1920s, when it became too difficult to find them (Stearns and Stearns 1999).  One individual, J.T. Gulick, the son of Hawaiian missionaries, "ransacked" the islands for tens of thousands of these colorful land snails, collecting 44,500 in three years (Stearns and Stearns 1999).  He alone caused the extinction of numerous species on the islands by encouraging rural residents to collect for him and by buying shells by the thousands, believing himself to be an important naturalist.  He was among the collectors who scoured the woods where these shells clung to trees and low bushes by the hundreds (Stearns and Stearns 1999).  Many were striped, while others were solid shades of ivory, yellow-gold and deep brown.  Some collections were of no scientific value because the locations where they were obtained were not noted.  No similar species remain in the wild today (Stearns and Stearns 1999). 
 
      In more recent times, exotic species of snails have been introduced onto islands for various purposes, preying on the native species. One expert estimated that when Captain Cook arrived in Hawaii in 1778, there were between 800 and 1,000 species of endemic Hawaiian snails from 11 families, but at present, only about 200 remain (Stearns and Stearns 1999).  Recent extinctions have been caused by deforestation and predation by exotic snails, including the giant African snail, introduced by the Hawaii Department of Agriculture to prey on another exotic snail.  Native snails feed mainly in endemic Hawaiian trees, another reason they have failed to adapt to the introduction of exotic trees and bushes.  Unusual among invertebrates, these snails reproduce slowly, one species needing 19 years just to replace itself (Stearns and Stearns 1999).  At least 49 species have become extinct in recent times, according to the Nature Conservancy's book, Precious Heritage: the Status of Biodiversity in the United States (Stein et al. 2000). The remaining species of Hawaiian land snail are endangered, and species are disappearing regularly from the wild, preyed on by exotic snails or rats and losing their host trees to logging (Stearns and Stearns 1999).  Conservation programs have not been well-funded, as these are among the least well-known of Hawaiian wildlife.
 
     On the island of Moorea in the Society Islands, the giant African snail was introduced as a food source, but when it became overpopulated, a carnivorous snail, Euglandia rosea, was introduced to prey on it.  Instead, the latter species preyed voraciously on native tree snails, exterminating all 11 species; it is now in the process of eliminating the native snails of Tahiti (Wilson 1992).
 
     Butterfly populations have declined from loss of host plants, pesticide use, over-collecting and loss of species upon which they depend.  The Xerces Blue (Glaucopsyche xerces) is the only native species in the United States to have become extinct in recent times.  It disappeared in the early 1940s, and the Xerces Society, dedicated to preserving butterflies, was named after it.  It is one of 38 butterfly species that recently disappeared around the world (Baillie and Groombridge 1996).
 
     Invertebrates play key roles in many of the world's ecosystems as food sources, for people as well as animals.  Some, such as coral and mollusks, create habitats for thousands of species.  Butterflies, mollusks and snails are among the planet's most beautiful creatures, yet conservation programs often neglect these important species.


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