Bugs Read online

  BUGS

  SIMON TYLER

  CONTENTS

  INTRODUCTION

  WHAT ARE BUGS?

  TYPES OF BUG

  THE BUG LIFE CYCLE

  THE ANATOMY OF BUGS

  EXTERNAL ANATOMY

  INTERNAL ANATOMY

  BUG EYES

  OTHER BUG SENSES

  BUG DEFENCES

  WHAT DO BUGS EAT?

  HOW DO BUGS EAT?

  HOW DO BUGS GET AROUND?

  WHERE DO BUGS LIVE?

  BEETLES

  BEES, WASPS AND ANTS

  BUTTERFLIES AND MOTHS

  TRUE BUGS

  DRAGONFLIES AND DAMSELFLIES

  FLIES

  MANTIDS, STICK AND LEAF INSECTS

  GRASSHOPPERS, LOCUSTS AND CRICKETS

  COCKROACHES AND TERMITES

  THE BIGGEST BUGS AND THE SMALLEST BUGS

  THE MOST DANGEROUS BUGS

  BENEFICIAL BUGS

  GLOSSARY

  INTRODUCTION

  Welcome to the fascinating world of bugs

  There are more bugs on our planet than any other type of animal, and still we only know about a small fraction of the number of bug species that are thought to exist. Scientists have described over a million of them, but there are likely to be many, many more out there waiting to be discovered.

  Bugs come in a staggering array of body shapes, sizes and colours. Some of them fly, others walk or crawl, some dig and some swim. They live in virtually every environment on Earth, from massive mountains to the deepest jungles, dry deserts to the surface of the oceans — even in high-rise city centres!

  The aim of this book is to give you a good understanding of bugs — their behaviour and their variety — and to celebrate the staggering range and beauty of bug life. We start by introducing topics about bugs in general — from what they are to how they live, how they use their senses and how they defend themselves from predators. We then investigate the different types of bug in more detail.

  The illustrations aren’t to scale. We’ve shown the insects larger than life so that you can see them in detail, but each is noted with its actual size.

  In parts of this book you may find some scientific terms that you are unfamiliar with. The first time these are used, they are highlighted in BOLD CAPITALS and all of these words and phrases are explained in the glossary at the end of the book.

  Blue fungus beetle

  Gibbifer californicus

  Length: 15mm

  Found in the southwestern USA and northern Mexico

  This beetle gets its name because of its diet — it likes to feed on rotting fungi.

  WHAT ARE BUGS?

  In this book we have used the word “bugs” to describe the entire CLASS of insects. Strictly speaking, only one section of the insect world is made up of bugs. “Bugs” is the scientific name used to describe members of the ORDER hemiptera but, because the word is so commonly used to describe insects in general, we have followed the convention of referring to the hemiptera as true bugs.

  One example of the hemiptera order is the Picasso bug – Sphaerocoris annulus – on the right.

  All bugs share certain CHARACTERISTICS which place them in the insect class:

  1 – They all have six legs, and so are known as HEXAPODS (from the Greek hex meaning six and poda meaning foot or leg).

  2 – They all have a hard outer skeleton, called an EXOSKELETON.

  3 – They all have a three-part body, made up of a HEAD CAPSULE, a THORAX and an ABDOMEN.

  Bugs are all part of the larger ARTHROPOD PHYLUM (category), which also contains arachnids (such as spiders and scorpions), myriapods (including centipedes and millipedes) and crustaceans (e.g. shrimp, krill, woodlice, crabs and lobsters).

  Picasso bug

  Sphaerocoris annulus

  Length: 8mm

  Found across Africa, including Kenya, Tanzania, Nigeria and South Africa

  Named after the Spanish artist Pablo Picasso, because of the similarity between the look of his work and its pattern. Like other shield bugs, it can release a squirt of nasty-smelling liquid to scare off potential predators.

  TYPES OF BUG

  As we have already learned, insects make up a class of animals. In biology, types of ORGANISM are grouped together into sets. This is known as TAXONOMY.

  The differences between bugs have led scientists to separate them into orders, FAMILIES and SPECIES.

  RED BULL ANT

  CLASS

  Insecta

  ORDER

  Hymenoptera

  FAMILY

  Formicidae

  GENUS

  Myrmecia

  SPECIES

  Myrmecia gulosa

  For example, consider the red bull ant on the left. The scientific name for this type of ant (known as the BINOMIAL name) is Myrmecia gulosa.

  That name tells us the ant’s species. A species is a single type of living organism that breeds to produce FERTILE offspring.

  The first part of the name – Myrmecia – is known as the GENUS. The genus is a set that the ant belongs to. Other ants in the same genus will be very similar, but will perhaps have some small differences, such as their shape, size or where they live.

  All ants belong to another, bigger set, which is known as the family. The ant family is called formicidae. Every type of ant on Earth (living or extinct) belongs to this family. Even ants that haven’t been discovered yet form part of this set.

  The ant family and other families (including the bee family and wasp families) form an even bigger set, known as an order. In this case, the order is called hymenoptera.

  The hymenoptera order and other orders form an even bigger set, called a class.

  As we already know, this is the insect class, known as insecta.

  THE BUG LIFE CYCLE

  Most bugs lay eggs, and their young develop through a series of stages. Certain insects such as butterflies, moths, flies, wasps, bees and beetles undergo a process such as the one shown below. In this process, the bug takes various different forms between the egg stage and the adult stage.

  THE TAILED JAY BUTTERFLY – FROM EGG TO ADULT

  An adult female tailed jay lays an egg on a leaf. The egg usually takes between three and four days to hatch.

  A caterpillar (known as a LARVA) hatches from the egg. It is very small when it first emerges, but it has a big appetite and as it eats, it grows much larger.

  Bugs such as cockroaches and grasshoppers undergo a simpler process in which a smaller version of the adult emerges from the egg. This is known as a NYMPH. The nymph grows, shedding its outer skeleton in stages before finally reaching its adult size.

  A small number of bugs (such as APHIDS) give birth to live young, but this is not very common.

  The caterpillar then becomes a PUPA. This process is known as METAMORPHOSIS. The pupa is fixed to a leaf and remains there whilst the caterpillar’s body breaks down into goo and reforms into a butterfly.

  The fully-formed butterfly emerges from the pupa after about two weeks, and then flies away. The insect’s final adult form is known as the IMAGO.

  THE ANATOMY OF BUGS

  Bugs come in all shapes, sizes, colours and patterns. Despite that, all bugs have the same basic body structure.

  EXTERNAL ANATOMY

  Despite their vastly differing shapes, most bugs have a relatively similar anatomy. Here we look at the external features of the giant burrowing cockroach – Macropanesthia rhinoceros.

  As we already know, all bugs have a head (1), thorax (2) and an abdomen (3).

  Bugs also all have sensory antennae (4) attached to their heads.

  The bug’s thorax is divided into three different areas, the front prothorax (5), central mesothorax (6), and rear metathorax (7).

  Si
milarly, the bug’s legs are described according to their position, with the foreleg (8) in front of the middle leg (9) and the hind leg (10) at the rear.

  The CERCI (11) at the bug’s rear are sometimes sensory organs or can also function as pinching weapons. In many bugs they no longer have any useful function and are then known as VESTIGIAL STRUCTURES.

  On the underside of the head are the mouthparts (12).

  The section of the leg that attaches to the bug’s thorax is called the coxa (13). The next section is called the trochanter (14).

  The femur (15) and tibia (16) usually form the longest section of the bug’s leg.

  At the end of each leg is the tarsus (17), which is usually formed of five separate segments. At the end of the tarsus is a pair of claws (18). Some insects also have pads on the base of the tarsus, known as arolia.

  Bugs which do a lot of digging often have larger, more heavily muscled forelegs. Jumping bugs typically have much longer hind legs that help them to leap high into the air.

  INTERNAL ANATOMY

  Most bugs also share similar internal anatomy. Here we see the internal structure of the western honey bee – Apis mellifera.

  The bee’s brain (1) is in its head. It connects to the rest of the nervous system via the nerve cord (2) which runs along the bee’s belly.

  The bee produces saliva in the salivary gland (3), which is connected to the salivary duct (4) near its mouth (5). The saliva helps with digestion and also when the bee is feeding larvae in the nest. Food that the bee eats passes along a tube called the oesophagus (6) into the crop (7) where it is stored. When the bee returns to the nest, it can regurgitate nectar from the crop to be stored in the nest. The remaining food (mostly pollen) passes into the stomach (8) where it is digested. Nutrients and water are absorbed in the intestine (9), and then waste is held in the rectum (10) before being excreted out of the anus (11).

  The bee’s heart (12) pumps its HAEMOLYMPH forwards, towards the brain via a tube called the aorta (13). The bee’s poison sac (14) stores the toxic chemicals for its sting (15).

  The bee breathes with an air sac (16) that pumps in air through holes in the abdomen called spiracles (17). The bee produces wax for nest building in wax glands (18) on its lower abdomen.

  BUG EYES

  Most bugs have COMPOUND EYES, which are made up of hundreds of separate units called OMMATIDIA grouped in a pattern like a mosaic. These are usually found on either side of the bug’s head (such as the bluebottle fly – Calliphora vomitoria – below) but can also meet in the middle of the head.

  Compound eyes allow a very wide field of vision. This helps bugs to spot any PREDATORS lurking to the side or even behind them. They are also good for judging distances – useful to help hunting insects to pounce on their prey.

  Certain bugs have both large compound eyes and simple eyes, known as OCELLI. These are often found towards the back or top of the head (such as the red ocelli on the head of the African mantis – Sphodromantis lineola – below). Bugs do not use ocelli to see, but to detect small changes in light levels. This helps them to find their way around by positioning themselves compared to the sun.

  Certain insects (usually those that live in caves or underground) have just ocelli, or sometimes no eyes at all. They instead use other senses to navigate their world.

  OTHER BUG SENSES

  As well as using their eyes, bugs have other ways of sensing the world around them. The main way they do this is through the use of their antennae. All adult bugs have antennae, but their shape, size and sensitivity varies across species.

  The main function of the antennae is to detect smells. Each antenna has sensors called OLFACTORY RECEPTORS that detect the presence of the chemicals that produce smells. It then transmits this information to the bug’s brain. The chemical smells might be caused by food, or by the presence of other bugs.

  If smell is very important to the bug, the antennae tend to be more complex, with feathery fronds. These increase the area of the antennae, to boost sensitivity.

  Bugs also use their antennae as feelers. Touch sensors in the antennae allow the bug to sense the presence of objects in front of them. These sensors can also detect wind movement and vibrations.

  Some bugs also have other sense organs on different parts of their bodies. Crickets have hearing sensors called TYMPANEL ORGANS on their hind legs, and grasshoppers have similar sensors on the sides of their abdomen.

  Some insects, like flies, have taste-detecting sensors in their feet, allowing them to identify sweet foods just by landing on them!

  BUG DEFENCES

  Because of their small size, many bugs are vulnerable to being eaten by predators, including other bugs. For that reason, they have evolved a number of defensive strategies to protect themselves.

  POISON and BRIGHT COLOURS

  Because bugs in the larval stage can be vulnerable to attack, many have evolved effective defences. The cinnabar moth caterpillar – Tyria jacobaeae – below, eats poisonous ragwort leaves, and this toxin builds up in the caterpillar’s body. If a predator tries to eat the caterpillar, it will taste disgusting, and may even kill them. Because the species has evolved a distinctive bright yellow striped pattern, predators have learned to avoid eating them.

  WEAPONRY

  Bugs often have spines, stings and large mouthparts that they can use to defend themselves. Certain beetles can respond to an attack aggressively, and species such as the mudflat tiger beetle – Cicindela trifasciata sigmoidea – above, will give a painful bite. Other bugs, such as the Asian giant hornet – Vespa mandarinia – have powerful stings which can seriously hurt or kill anything that tries to eat them.

  DISGUISE

  Certain bugs, particularly butterflies and moths, such as the io moth – Automeris io – above, have patterns that resemble a large pair of eyes. These trick potential predators, such as small birds, into thinking that the bug is actually a dangerous, larger bird.

  BUG SPRAY

  Other bugs have evolved a particularly off-putting defensive mechanism – they are able to spray or squirt foul liquids at any would-be predators. For example, the green shield bug – Palomena prasina – left, can produce toxic chemicals in a gland on its abdomen. When it feels threatened, it can eject this chemical as a liquid, which deters most predators.

  WHAT DO BUGS EAT?

  Bugs eat an enormously varied range of foods, and have developed all sorts of clever strategies for getting it. They have also evolved some amazingly complex mouthparts to help them suck it up or gobble it down. Some are even able to grow their own food.

  Many insects are CARNIVOROUS predators, including mantids, dragonflies, some true bugs and some beetles. Tiger beetles are, for their size, one of the most formidable predators on Earth. They can move very fast, and catch other insects and spiders with their powerful, sharp mouthparts.

  Dragonflies are brilliant aerial predators, and can catch and eat their prey during flight, without putting a foot on the ground.

  Most butterflies and moths have developed specialist mouthparts adapted to drinking liquid food, such as plant nectar, tree sap and rotting fruit juices.

  Others are more adaptable, such as bees, which can lap up liquid nectar and also deal with solid food too, such as pollen.

  Some ants and termites bring plant material into their nests, onto which they are able to grow fungi. They then use the fungi as a source of food – ingenious!

  The diet of many insect species even differs between the males and females. For example, the females of many flies such as mosquitoes, horseflies and biting midges drink blood, but the males feed on nectar. This is because the females need extra proteins from a blood meal to produce eggs. This strategy is known as ANAUTOGENY.

  Most bugs ensure that their offspring can eat when they hatch by laying eggs on the larvae’s preferred food. For example, burying beetles get their name because they actively search for small dead rodents or birds. They then dig a hole and bury the dead creature, and the fe
male lays her eggs on it. When the larvae hatch, their parents feed them from the rotting carcass.

  The differential grasshopper – Melanoplus differentialis – opposite, has a voracious appetite and particularly likes the young shoots of farmed crops such as corn, soy and fruit trees. Swarms of these grasshoppers can destroy huge volumes of crops, which is a major problem for farmers in the southern United States and Mexico.

  HOW DO BUGS EAT?

  Butterflies and moths use a long tube called a PROBOSCIS to suck nectar from flowers. The eating method that these bugs use is called SIPHONING. The bug’s proboscis is flexible and it can curl up into a tight roll when not being used for feeding. They can be very long, in the case of the Morgan’s sphinx moth – Xanthopan morgani – over 300mm in length.

  Bees have a tongue-like structure called a LABIUM. They use this to dip into nectar or honey, which is picked up on tiny hairs and then drawn into the mouth with a pumping action. Bees also have MANDIBLES, but these are mainly used for shaping nest materials.

  Some bugs, such as beetles, mantids and ants, have two large appendages called chewing mandibles, which they use to bite, tear and chew their food. Smaller structures underneath the mandibles, called MAXILLARY PALPS, transfer food into the mouth. Bugs that eat in this way are known as mandibulates.

  True bugs, fleas, sucking lice and biting flies (such as mosquitoes) also use a proboscis for feeding. However, the proboscises used by these bugs are rigid and are used for piercing tissue and then drawing liquids out of both animals and plants. The eating technique that these bugs use is called pierce-sucking.