The Galápagos insect fauna is both poor in variety and in numbers. Nevertheless, there are about 1,000 species of insect in the Galápagos. Unlike mainland Ecuador, where insects are a conspicuous component of forest life, most Galápagos insects must be searched for and few are attractive.
The arid, almost desert-like, climate of much of the archipelago's land area provides an inhospitable environment for most insect species. It is therefore not surprising that most Galápagos insects are nocturnal to avoid the desiccating sun and spend the daylight hours hidden in dark humid places. This in part explains why most are hard to find and why few are colorful.
Though poor in species number, the Galápagos insect fauna is often abundant, especially during the warm/wet season. Insects have adapted in many ways to the harsh Galápagos environment. We will break up our discussion into the major orders of insects: Beetles (Coleoptera), Ants, Wasps and Bees (Hymenoptera), Butterflies and Moths (Lepidoptera), True Bugs (Hemiptera), Grass Insects (mantis and grasshoppers), and Scorpions, Spiders and Centipedes. Other orders of insects are found here as well, but in the interest of focus we will confine ourselves to these.
Beetles -- Coleoptera
Some 200 beetle species are found in the Galápagos. Most of these are small and inconspicuous. Some of the more noticeable species are:
Stenodontes molarius -- A large beetle with long antennae and powerful jaws. The larva of this species bores in wood and causes damage to trees. The grubs of longhorn beetles are an important food source for the tool-using woodpecker finch.
Calosoma spp. -- These ground beetles are shiny green-black with long legs. They are fast runners and active predators. There are three species in the Galápagos, two of which are flightless.
Trox suberosus -- One of the scarab family. Its larvae live in the eggs of reptiles, especially the green sea turtle, causing considerable mortality in the nests. Other members of this family breed in dung, in particular that of giant tortoises.
Gersteckeria sp. -- A cactus eating weevil about 0.6 cm long. It is dark brown with a long, curved "snout" and some creamy spots. The adults and young feed on cactus pads.
Cincindela sp. -- Two species of tiger beetle are known. These fast running predators have similar habits to the Calosoma beetles.
Ants, Bees and Wasps -- Hymenoptera
There are about twenty native ant species, a few wasps and only one bee in the Galápagos. Some of these are:
Carpenter ants; Camponotus sp. -- These yellow-brown ants bore galleries in wood for their nests.
Little fire ant; Wasmannia auropunctata -- This species is a recent introduction and a serious pest. Only 2 mm long, it has a vicious bite and sometimes is so abundant that farmers have to leave their fruit and coffee unpicked. It also preys on and out-competes other native ant species. Great care should be taken not to transport this species to islands where it does not occur. It is presently found on Santa Cruz, Isabela, Santiago, San Cristóbal and Floreana. It is easily transported on fresh fruit and vegetables.
Carpenter bee; Xylocopa darwini -- This is a solitary bee which makes its nest in wood. The black females are often seen visiting flowers where they collect nectar and pollen. They are one of the most important insect pollinators for Galápagos flowering plants. The males are yellow-brown, smaller, and much less abundant. Males set up territories in which they make figure-of-eight flights to court females.
Butterflies and Moths -- Lepidoptera
Eight species of butterfly and many species of moth are known from the Galápagos. This is a low diversity, but quite a few species are commonly seen. Butterflies by day and moths by night are important pollinators of flowers. Because of the hot dry nature of the daytime environment, a high proportion of Galápagos flowers are white, indicating the advantages of night-time pollination.
The larvae, or caterpillars, of butterflies and moths are vegetarian, and can be found feeding on most Galápagos plant species. Many caterpillars are highly host-specific and can only survive on one type of plant, while others are fairly catholic. Like most other insects, they are most frequently seen during the warm/wet season when humidities are higher and there is more vegetation available. Sometimes caterpillars of some species become so abundant locally that they completely defoliate their host plants. This occurs with different species of plants and caterpillars in different parts of the archipelago at different times and shows that the Galápagos environment is an unpredictable one with few regulatory controls for insect populations. Caterpillars and adult lepidopterans are an important food source for many birds, even seed-eating finches feed their young on small caterpillars.
Butterflies have clubbed antennae and usually fold their wings vertically. Moths usually fold their wings horizontally and over each other.
Galápagos sulphur butterfly; Phoebis sennae marcellina -- This is the only yellow butterfly in the islands. It is a small subspecies of a species that occurs throughout the Western Hemisphere. It is common and wide-spread in the islands.
Galápagos silver fritillary; Agraulis vanillae galapagensis -- This medium-sized (5 cm) black and orange butterfly, with silver spots on the underside, is commonly seen from the coast to the highlands.
Painted ladies; Vanessa spp. -- Two species, V.carye and V. virginensis, are locally abundant. Both are red, orange and black above, like the fritillary, but with pastel-colored underwings.
Monarch butterfly; Danaus plexippus -- This is the largest Galápagos butterfly (10 cm across wings). It is the same species as the well-known migrating Monarch of North America. The wings are brownish-red with black veins and wing tips. There are white spots on the wingtips and trailing edges.
Queen butterfly; Danaus gilippus -- Similar to the Monarch, but smaller and less heavily marked with black on the wings. This species is found on Isabela. The bright colors of this and the above species indicate the distastefulness of these species to birds. Once tasted, twice shy.
Leptodes parrhasioides; Galápagos blue butterfly -- This beautiful little blue butterfly is endemic to the islands and common within them. It is alert and does not allow close approach. It has a fast fluttering flight as it moves about the vegetation.
Large-tailed skipper; Urbanus dorantes -- This little brown butterfly has large blunt "tails" to its hind wings and a few yellowish spots on the fore wings. It is common in the highlands of the larger islands, especially in open areas.
Green hawkmoth; Eumorpha labruscae -- This species is common and wide-ranging. Though the larvae feed on a vine in the humid and transition zones, the adults are often found in the arid zone and have been caught at the lights of boats well out to sea. Hawkmoths, especially this species, are rapid fliers. The adults feed on the nectar of flowers and have a very long tongue or proboscis. The proboscis of this species is almost twice as long as the insect's body. When feeding they look much like hummingbirds or small bats.
Hawkmoth; Hyles lineata florilega -- this Galápagos subspecies of an almost cosmopolitan species is widespread and common in the islands. It often comes to lights on boats and is easily recognised by the striking black and white lines on its wings. Its larvae are green with black and yellow stripes and a long curved yellow-red "tail." It is usually found on Portulaca.
Hawkmoth; Manduca rustica calapagensis -- This mottled grey-brown species is common at lights. Its larvae are green to purplish with yellow speckling and oblique white stripes edged with purple. The tail horn is yellow-green. The larva feeds predominantly on Cordia and Clerodendrum, which it frequently defoliates.
Footmen moths; Utethesia spp -- These white, day-flying moths are attractively black and red spotted with red underwings that are displayed when disturbed. Four species occur in the Galápagos, two of which are quite common at most elevations up to the humid zone.
Noctuid moth; Ascalapha odorata -- this is the largest moth in the Galápagos with a wingspan of up to 15 cm. its coloration is nondescript dark brown and it is found on many islands. It is usually seen around dusk.
Atteva sp. -- this small and brightly colored moth is occasionally abundant on Scalesia plants in the arid zone.
Praying Mantis -- Mantodea
One species, Galapagia solitaria, is found in the Galápagos. Pale brown, it blends well with the dry vegetation of the arid lowlands. It preys on other insects.
Grasshoppers, Locusts, Katydids and Crickets -- Orthoptera
Twenty-one species of this order are found in the Galápagos. Amongst the short-horned grasshoppers (Acrididae) is the brightest and most conspicuous Galápagos insect -- the painted locust, Schistocerca melanocera (see color plates). This species is black, red, green, and yellow and is abundant in the lowlands. These are popular prey for the lava lizards. Two other genera of grasshoppers, Sphingonotus and Halmenus, are also found, but these are smaller and well camouflaged. Species from these genera have diversified somewhat within the archipelago.
Katydids, or long-horned grasshoppers (Tettigoniidae), occur in the islands. they are most active at night when their shrill, loud, song can be heard during the warm/wet season. Like most other members of this order, they are vegetarian. There are also crickets (Gryllidae) in the Galápagos.
Two species of scorpion are found in the Galápagos. These are the endemic scorpion, Centruroides exsul, and the common yellow scorpion, Hadruroides lunatus. The former is uniformly reddish-brown to dark brown with slender pincers, while the latter is yellow with stockier pincers. Both species are predators of insects and other arthropods, which they hunt at night. They sense their prey largely by vibrations in the air and ground. They are in turn often eaten by lava lizards; the scorpion's sting seems to have little effect on reptiles. During the day they hide under rocks and vegetation.
The courtship of scorpions is usually only observable in captivity, but it is a magnificent pas-de-deux. The male will lock pincers with the female and then deposit a spermatophore (packet of sperm) on the ground. He then "dances" with the female until he able to manoeuvre her onto the spermatophore. Frequently, the male is eaten by the female after mating; he is much smaller. Young scorpions develop within the mother's body. At birth, the tiny white young clamber onto the mother's back where they remain for a week or two until they are able to look after themselves.
Hadruroides lunatus is found on most of the major islands except for Española, Genovesa, Marchena, and Pinta, while Centruroides exsul is found only on Santa Cruz, San Cristóbal, Pinta, Española, and Floreana. Both live in the arid zones of these islands. The stings of these scorpions can be painful but are usually not serious.
There are over fifty species of spider in the Galápagos. Many of these are widely distributed; few are endemic. Galápagos spiders fall into two main groups: hunting spiders and orb web spiders. The former do not weave webs but actively chase their prey over the ground or on walls and ceilings. The latter group usually make a new web each day and wait either on the web, or near it, for their prey to become entangled in the sticky silken fibres. Spiders do not usually chew their prey but inject digestive juices into their hapless victims and allow the digestive processes to occur in the victim's body. They then suck out the resulting liquid, leaving empty exoskeletal husks.
Two of the most frequently encountered hunting spiders are the giant crab spider (Heteropoda venatoria) and the smaller Selenops sp. Both of these species live in houses and other buildings where they chase around at night after insects. Despite their formidable size, both these species are beneficial to us as they prey on many tiresome insects, Heteropoda females can often be seen carrying their whitish egg sacs under the body. Female spiders are usually larger than the males and only mate once. They can store sperm and lay several batches of eggs. Males often mate with many females.
A relative of the black widow, the endemic Lathrodectes apicalis is common and is found in rock crevices and under fallen tree trunks. It spins a small web in front of its "burrow." Its abdomen is black with one yellow and three red stripes. Beware of this species as its venom may be dangerous.
Orb web spiders build large, typical, "spider webs" between vegetation and other objects to trap flying insects in their sticky threads. An often seen species in the Arid Zone is the silver argiope, Argiope argentata. Its back is silver and black and it characteristically sits in the middle of its web in a X-posture. The web itself often has an X-shaped design of white silk in the center. Another species, Neoscona cookoni, makes a very large web which is often strung across paths. It sits on its web at night, but usually hides by day in the vegetation nearby. these webs can be so abundant at times that it is impossible to walk more than a few metres without encountering one.
The most beautiful Galápagos spider is the star spider, Gasteracantha servillei. This species has a hard, shell-like and spiny abdomen that dwarfs the rest of the body. This dramatically sculptured abdomen is bright yellow and black. They are found commonly in mangroves and other shore vegetation near lagoons and are also found up to the humid zone.
The young of many web-spinning spiders secrete a long thread of silk that enables them to be carried long distances from their birthplace. This is probably the manner in which these species reached the islands. The use of these "parachutes" enables them to colonize islands effectively and is probably why there are few endemics.
Centipedes -- Chilopoda
There are a number of centipede species in the Galápagos. One, the endemic Scolopendra galapagensis, may grow as large as 30 cm. This species is common in the Arid Zone of most islands where it preys by night on insects, lizards, and even small birds. It has a dark brown body and reddish legs. During the day, the centipedes usually hide in crevices and under rocks and fallen trees. They are eaten by the Galápagos hawk, night herons and some mockingbirds. Centipedes kill their prey with a venom that is injected through the tips of their poison claws. The bite can be very painful to humans. This has given them the honour of being the most feared Galápagos creature.