Cark Op I I Ik Young

Parental care of eggs and young is common in some centipedes, arachnids, and insects. Some female spiders wrap their eggs in silk and carry them around, or stay close by until they hatch. Scorpions and some other arachnids brood their eggs and carry recently emerged young on their backs. Among insects, it is usually the female who takes responsibility for "child-care," but the males may also play a part in some families.

Migratory Insects

coloration o f t ige moth indicates its unpalatahility

VlKTHODS OK SKU -1)1,1 KNSK An arthropods first line of defense is its cuticle, which may be very tough or leathery. Sharp, cuticular spines and protrusions, such as warts and bumps, or the ability to roll up into a ball, may further increase the protection that the exoskeleton prov ides. Mandibles and limbs arc effective when used to strike out at enemies - the kick from a locust s hind leg can draw blood in most predators.

Physical defenses arc enhanced by producing unpleasant sounds, or repellent chemicals or odors. Many bugs, for instance, produce strong-smelling compounds from thoracic or abdominal stink glands. Sap-sucking bugs, such as aphids, often surround themselves w ith "bodyguards" in the form of ants: the ants arc attracted to the sugar-rich honeydew (excrement) that the bugs produce, and in turn help protect the aphids from predators. Some arthropods arc brightly colored, which may serve to warn predators of their toxicity; sometimes eyespots and other bright patches arc flashed at predators in order to startle them.

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Many insects have evolved to blend into their surroundings, or to mimic dead ¡eaves, sticks, thorns, bird droppings, stones, or even other, more dan get o us, spet ies.

A Warn ino Colors

Bright, contrasting warning colors advertise the presence of chemical defenses. Some species "cheat," and are not actually poisonous at all.

A Poisonous Pricklks

Toxic chemicals may be made inside the body or obtained from a poisonous food plant. These chemicals are often stored in outer parts of the body.

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30 ♦ INTRODUCTION

Social Insects

M ost arthropods lead solitary lives, coming together only for mating. Some might be considered gregarious, grouping together for safety or sharing a food source. I lovvever, trtdy

"social" species (all termites and ants, some wasps and bees) are characterized by cooperation within a colony to rear young, coupled with a division of labor, and an overlap of generations.

outer envelope surrounds paper combs

Social Wasps and Bees

In these highly social insects, the reproductive females, or queens, found and head the colonics. The queens lay eggs, then rear a few workers (sterile females) themselves. Thereafter, the queen leaves nest-building, colony defense, and feeding and tending the young to the growing number of workers. Mated queens can determine the sex of their offspring by withholding sperm if a male is preferred (males are produced from unfertilized eggs, females from fertilized ones).

outer envelope surrounds paper combs

A Wasps' Nest

Yellow jackets and hornets make exposed or underground nests of paper made from chewed wood fibers, lite horizontal cells contain the developing larvae.

yellow jacket worker extends the nest

< Honeycomb

The honey bee's nest consists of vertical wax combs divided into hexagonal cells, in which young are reared and honey is stored.

Migrating Inskcts

Some arthropods undertake regular migrations from one place to another to find food or egg-laying sites. Army ants (see p. 184) and swarming species, such as the migratory locust l.ocusta migratoria (Acrididae, see p.64), are good examples of migratory insects. The longest insect migration is that of the Painted Lady butterfly, Cynthia cardui (Nymphalidae, see p. 174), which can travel approximately 4,000 miles (6,440km) from North Africa to Iceland. Some spiders can be blown for hundreds of miles in wind currents.

Long-distance Travelers

The Monarch butterfly (Danaus plexippus), a notable migrant, travels from winter roosts in Mexico to North America and Canada.

Ants

These highly social insects, which belong to the large family Formicidae, are very abundant and have a great impact on terrestrial ecosystems. In most habitats, they are the major predators.

Ants live in colonics ranging from a handful of individuals to tens of millions. They usually have female (queen), male, and worker castes. The workers are all wingless, sterile females; the larger ones may function as soldiers to defend the colony. Reproduction usually occurs between winged males and females. After mating, the males usually die and the females lose their wings. The caste is mainly determined by the food that the larvae are fed by the workers: a diet low in protein will lead to the production of another worker, whereas a diet high in protein will produce a queen. The soldiers head and jaws are often modified according to the caste and species, and may be specialized for crushing seeds or dismembering enemies.

ants cooperate to carry leaf

AV Lkat-ct t'tkr Ants

In Central and South America, leaf-cutter ants (Atta species) are major herbivores and among the most serious insect pests. Their subterranean nests can be more than 15ft (5m) deep and include millions of workers.

Tkrmitk Nkst

Depending on the species, a termite colony can range from a tiny nest to a vast structure both below and above ground.

Tkrmitks

'Termites, unlike many other insects, are able to digest cellulose. In some tropical regions, they are highly abundant and destructive and may eat up to one-third of the annual production of dead wood, leaves, and grass. Termites live in permanent social colonies and have a number of distinct castes. The colonies normally have a single queen, a king, and a few other reproductive males. There may also be supplementary reproductives, which will become active if anything should happen to the queen. Termite soldiers, unlike ants, are sterile males and females. Worker termites resemble the nymphs and are the most numerous caste. The role of the worker termites is to build and repair the nest, forage for food, and feed the young nymphs.

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Tkrmitk Nkst

Depending on the species, a termite colony can range from a tiny nest to a vast structure both below and above ground.

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The internal structure of many o f the larger termite nests allows air to circulate so that the temperature inside the nest can be regulated to within 2°F ( 1 (f. Stale, carbon-dioxide-rich air is vented to the outside.

Habitats

I nskc i s am) otiikr terrestrial .arthropods are found all over the globe, from snow-covered mountains to hot desert valleys, but they arc not evenly distributed. Apart from some species of mites and midges in the Antarctic and some blood-sucking insects, such as mosquitoes, in the Arctic, there are very few arthropods near the poles. The closer to the equator you go, the greater the number of arthropods, both in species variety and abundance.

Conservation

Mammals and birds used to be the only animals considered worthy of conservation, but a growing awareness of the vital role that insects play in global ecosystems is changing this view. Some rare insects are now protected by international law, and many countries are beginning to implement legislation. First and foremost, we must protect their habitats from destruction - then we must educate and limit collectors.

SURVIVAL STRATFCilFS The surv ival and persistence of most arthropod species has much to do with their relatively small size, protective cuticle, and ability to reproduce quickly (see p. 14), but many also have special strategies for survival. When conditions are too hot and dry, many species remain dormant, while other species hibernate where winters are cold. Several insects, notably some species of ants, are able to function in extremely high temperatures, in excess of 14() F (65°C). At the other end of the scale, some species are able to withstand excessively cold conditions, surviving temperatures as low as -40 I (-40 C).

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Tropical Forks ts

These lush, moist habitats cover a tiny part o f the total land area of the globe (about six percentyet they are estimated to hold approximately 50 percent of all the world's arthropod species.

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Tkmpkratk Woodland

Although less lush than tropical forest, temperate woodland has a rich and varied fauna. Fertile soil broad-leaved trees, deep leaf litter, and decay ing wood all provide ideal conditions for arthropods.

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Mountains

Species that live in mountains are adapted to cold\ wet, and windy conditions. Plant life becomes sparser inct easing altitude; a result, there are fewer species of arthropod.

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Braconid Wasp

Temperate CGrassland savanna

'The canopies of scattered tre tropical grassland harbor a rich, diverse arthropod fauna, particularly termites and ants. Overgrazing is endangering many species.

Braconid Wasp

Oaves and Deserts

(fwe-dwelling species adapt to survive in total darkness and high humidity. Many are blind and wingless. Desert-dwellers adapt to temperature extremes and arid conditions.

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Scorpion

Freshwater

Freshwater habitats have a unique arthropod fauna. (July about 5 percent of insect species are aquatic for part of their life cycle, yet their abundance means they contribute greatly . to aquatic food chains.

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