500 Insects: A Visual Reference

Introduction

Insects are overwhelmingly diverse ... so diverse you might well think it impossible to routinely recognize bugs, beetles and flies the way we expect at least a passing familiarity with most of the birds, mammals and other vertebrates that cross our paths. That perception is grounded in reality, since most known species of living things — about a million of the 1.7 million or so named species — are insects, and the number of insect species as yet undiscovered and unnamed undoubtedly runs into further millions. It all seems hopelessly overwhelming — but it shouldn't.

Insect diversity, especially the almost untapped diversity of little-studied insects such as tiny tropical flies, should be seen as a rich ore of insights to be mined for generations to come rather than as a barrier to the study of insect natural history today. In fact, most insects are relatively easy to identify to a meaningful level. The orders of insects — the big groups such as flies, beetles, dragonflies and wasps — are few and easy to learn, and most insect species (indeed, most animal species) belong to one of only four easily recognizable orders: flies (Diptera), wasps (Hymenoptera), beetles (Coleoptera) and moths and butterflies (Lepidoptera). These orders in turn are divided into families — such as fireflies, mosquitoes and lady beetles — most of which occur worldwide and are readily recognizable anywhere on the planet as variations on familiar themes. Many of the images in this book are from "exotic" places, but most should be easily recognizable as members of familiar families that probably occur in your own backyard, even though a disproportionate number of the species shown belong to rare families or families with unusually restricted distributions. Identification beyond the family level can be more difficult, and for many groups it has traditionally been the realm of specialists with microscopes, extensive libraries and reference collections. That is changing quickly; for more and more groups and more and more regions, identification right down to genus and species is getting easier, thanks largely to the digital revolution.

If you know the family to which an insect belongs, you can make generalizations about how it lives and what it eats, but more detailed information about insect distribution and behavior is often tied to generic (genus) or specific (species) names. In general, insects from temperate countries do have species names, and you can find the names for the most commonly encountered or distinctive species by using recent photographic guides. Identification of tropical insects is more daunting because of the huge numbers of undocumented species and a lack of published identification guides. Even in the tropics, however, many of the large and more conspicuous groups are remarkably well-known, and commonly encountered species are often easily identifiable. By way of illustration, most of the Bolivian insects illustrated in this book were photographed while I was instructing at a field course in primary rainforest near the Peruvian border. We were able to identify most of the more conspicuous insects encountered during that course through the use of a small photographic guide called Amazon Insects (Castner, 2000) illustrated with about 160 photographs from the Peruvian Amazon. More remarkably, during less than two weeks in the Bolivian rainforest we encountered most of the insect groups illustrated by Castner. This is not to say that either the photos in Castner's book or the 300 or so neotropical insects illustrated here represent a significant proportion of the millions of insect species thought to occur in the Amazonian rainforest, but it does suggest that they represent a meaningful proportion of the distinct kinds of larger insects an ecotourist might encounter during a visit to the South American rainforest. Similarly, the 80 or so species illustrated here from Costa Rica hardly scratch the surface of the insect diversity of that hyperdiverse Central American country, but if you go bugwatching in Costa Rica you will probably find significant similarity between the species shown and discussed here and the insects you spot along forest trails and margins.

The photographs in this book were identified partly by using reference collections, paper guides and websites, but many of the images were identifiable only with the help of specialists — professional taxonomists who have identified hundreds of my specimens and images over the past several years. Some kinds of insects, as I have noted, are so poorly known that several of the images here are of undescribed (new) species photographed for the first time. A few of the photographs in this book are identified only to the family level because I could not identify them further, nor could I find a specialist able to identify them for me. An enormous amount of basic taxonomy remains to be completed before tropical insects will be covered by accessible identification tools like the wonderful guides now appearing for many groups of insects in temperate countries.

Although this book will undoubtedly find use as a tool for identifying naturalists' digital images from bugwatching excursions near and far, it was not assembled as an identification guide, and it provides neither comprehensive coverage for any region nor balanced coverage across the Insecta. Instead, it is a compilation of images that illustrate insect diversity, form and function around the world. Most of the examples are drawn from the neotropics — Earth's major cauldron of diversity — but a few are from other areas, including Australia, New Zealand, temperate South America, the Pacific, the Caribbean and North America.

Insect Distributions

Since the images in this book were taken in lands scattered across half the planet, some comments on why which insects live where might be in order. If you check out the insects in your backyard or a city park, most of the species you encounter are likely to be secondarily widespread creatures that have travelled around the planet thanks to mankind's deliberate or accidental intervention. Ask a friend to name ten kinds of insects and I will bet that eight of them are European or Asian species that are now common in much of the world: European Earwigs, Cabbage White Butterflies, House Flies, most cockroaches, most crop pests, most common lady beetles, most common ground beetles, common hornets, yellowjackets and paper wasps — the list goes on and on, as does the stream of new invaders arriving on foreign shores to displace native species. A few such invaders are included here, but most of the insects on the following pages were photographed in native ranges that still reflect the pre-human history of the planet, ranges that are Earth's collective memory of origins, expansions, divisions and contractions of habitats. Hundreds of millions of years of planetary change have divided, subdivided, recombined and divided species ranges again and again, driving speciation and generating the biodiversity that defines life on Earth today.

When you look at a picture of an insect from an exotic place, try to think of where you have seen something similar. The odds are that the similarity you see reflects relationship, and that the insect belongs to a recognizable genus, a familiar family or at least a known order. At some point in the near or distant past that exotic insect shared a common ancestor with something you know. That bug from Cuba, for example, might have a very close relative in the American southeast, and those two species in turn might be very similar to a member of the same genus in northeastern North America. Related species are often similar because they resemble a common ancestor that was somehow subdivided — perhaps by a barrier such as a mountain range or body of water — into populations that evolved into different species. Professional taxonomists routinely plot phylogenies (like genealogies that show the relationship between species rather than individuals) of groups of related species against the geographic distribution of the species, and in doing so often show neat matches between the divisions in the phylogenetic trees and the divisions between areas or patches of habitat. Generally, the more distant the relationship between exotic insects and those you know, the longer they have been separated. Thus, some insects from Central America look much like exotic versions of North American species with which they share a relatively recent common history, while Australian or Chilean insects are, in contrast, often strikingly different from the insect groups familiar to most North Americans and Europeans.

One of the terms frequently used in this book is the term endemism (or endemic). An endemic species is a species that originated in an area and still occurs there; for example, the termites illustrated on page 54 are found on Robinson Crusoe Island (one of the Juan Fernandez Islands of Chile) and nowhere else, and are thus endemic to one island. Islands typically have very high endemism, as do other isolated areas such as mountaintops. Australia and Chile are examples of countries with very high endemism because of their isolation from other countries where related insects occur — Australia because it is an ancient island, and Chile because it is bounded by water to the west and south, mountains to the east and desert to the north.

Collecting and Photographing Insects

The study of insects in the field — let's call it bug-watching, since it has much in common with the more limited hobby of birdwatching — usually involves capturing a specimen or image for study, identification and permanent record. The traditional approach to insect study has been to capture and kill specimens, usually preserving them as dried exoskeletons impaled on pins, and later identifying them by using a hand lens or microscope to examine morphological details described in printed keys or identification guides. This apparently anachronistic approach is still necessary for serious specimen-based studies of insect systematics, but bugwatching as a natural-history pursuit is enjoying an overdue resurgence of popularity because it is now possible to go out and "capture" specimens with digital cameras and assemble a digital collection without killing anything, and without the hassle of getting collecting permits, poisons, pins, labels, storage boxes and the other paraphernalia of the professional entomologist. Furthermore, it is now possible to identify an ever-increasing range of insects merely by matching your digital images to similarly shaped and colored images in recent books and on the Web. This is not to suggest that the millions of insect species out there can all be identified by color and shape, but an impressive proportion of those you are likely to digitally collect are distinctive and can be recognized from good images.

Good images of insects down to mosquito size and even below can be obtained with most digital cameras, even the small pocket-sized cameras, with a bit of practice and a lot of patience. The trick to insect photography is to get to know your subjects and to approach them slowly; whether you then shoot them with a pocket "point-and-shoot" or a fancy digital SLR (single-lens reflex) camera is unimportant. Excellent images for Web-posting or developing a digital insect collection can be obtained using pocket cameras, but the images for this book were taken with larger SLR cameras. A few were taken using film cameras equipped with macro lenses and flash units, but most were taken with the same lenses on newer digital SLR bodies.

Basic Bug Biology

The pictures in this book usually show adult insects, but bear in mind that most insects have fascinating life cycles that include wingless immature and winged adult stages. Everybody is familiar with the life cycle of a butterfly: it starts with an egg that hatches into a wingless larva (caterpillar), then transforms into a pupal stage that later undergoes another metamorphic molt to the familiar butterfly stage. This kind of development, called complete metamorphosis, characterizes most members of the big, familiar orders (beetles, flies, wasps, moths) and many smaller ones, but even within these orders there are lots of variations on the theme. Loss of wings, for example, is common (ants and fleas, of course, but also wingless flies, beetles and even wingless moths), and several groups bypass the egg stage. Not all insects undergo complete metamorphosis; many orders of more "primitive" winged insects hatch from eggs not as wingless larvae, but as nymphs with small wing buds that later burst into complete wings without the need for a pupal stage. Grasshoppers, dragonflies, mayflies and true bugs experience this kind of development. A few, still more primitive insects predate the origin of wings; in their simple development each successive stage looks like the one before. The stages in an insect's development are made necessary by its external skeleton, which is like a suit of armor that has to be periodically discarded and replaced with a bigger one as the insect grows. These stages, or instars, are punctuated by molting, or casting of the old skin, which is soon replaced by a new and larger exoskeleton.

Basic Bug Structure

This book is restricted to the class Insecta, a special group of invertebrates with certain defining attributes. They have an external skeleton and jointed appendages, which puts them in the phylum Arthropoda, but they differ from other arthropods in having a single pair of antennae, a pair of (generally) chewing mouthparts called mandibles, and — most important — six legs. The body is divided into a head, a thorax and an abdomen that usually lacks appendages other than those involved in mating and laying eggs. The thorax is the muscle-packed section that supports the legs and — usually, and unlike all other invertebrates — one or two pairs of wings, while the head is modified characteristically in each order of insects. The mouthparts of beetles, grasshoppers, wasps and many other insects adhere to the basic design of chunky chewing mandibles followed by segmented maxillae that help in food manipulation, but those of moths, flies and true bugs are much modified, with missing or inconspicuous mandibles. Moth mouthparts are usually dominated by a coiled, straw-like proboscis, most flies have sponge-like mouthparts, and true bugs pierce their food with hypodermic syringes made of slender drawn-out mandibles and maxillae.

The Ins and Outs (and -inis and -inaes) of Taxonomic Names

The class Insecta is divided into orders, which are mostly big, familiar groups such as Lepidoptera (butterflies and moths), Diptera (flies) and Coleoptera (beetles). There are no standard endings for order names, but they often end in -ptera, which is Greek for "wing." Lepidoptera translates as "scaly wing," Diptera translates as "two wing" and Coleoptera translates as "sheath wing." Orders are divided into families, and family-level identification is the secret to appreciating the world of insects — which is a good thing, since it is often difficult to identify them beyond the family level. You can always recognize a family name by the ending -idae; for example, Muscidae is the House Fly family and Carabidae is the ground beetle family. Larger families are often divided into subfamilies, and the subfamily level can be very useful in large groups such as the Scarabaeidae (scarab beetles). You can always recognize a subfamily name by the ending -inae, as in Rutelinae (the shining leaf chafer subfamily). In a few groups the subfamilies are further divided into tribes, which are always given names ending in -ini. Subfamilies and tribes are given here only where they are of special interest.

All species are grouped into genera, and species names are always given in combination with the generic name; for example, Acromyrmex versicolor is a Southwestern American species in the genus Acromyrmex. In a scientific work it is proper form to cite the author of a species following the first use of the species name, so if this were a scientific work the correct way to refer to the Desert Leafcutting Ant would be Acromyrmex versicolor (Pergande), since Pergande named this species (his name is in brackets to indicate that he originally described the species in a different genus). Since this is not really a scientific work, I have excluded author names to make the text a bit more readable. Generic and species names are always in italics, with the genus name (but never the species name) capitalized. Formal common names that refer to a single species are always capitalized, as are formal scientific names for families, tribes, subfamilies and orders. Thus we have the Desert Leafcutting Ant (Acromyrmex versicolor), a common species in the genus Acromyrmex in the tribe Attini (leafcutting ants) of the subfamily Myrmicinae (a group of stinging ants including fire ants and leafcutting ants) in the family Formicidae (all ants) in the order Hymenoptera.