Read an Excerpt

CHAPTER 1

INTRODUCTION TO GARDEN INSECTS AND THEIR RELATIVES

WITH FEW EXCEPTIONS, the animals covered in this book are all classified as members of the phylum Arthropoda — the arthropods. As such, all share certain physical features, including:

— division of the body into segments;

— an external skeleton (exoskeleton) and growth that requires periodic shedding of the exoskeleton (molting);

— jointed appendages;

— internal structures that include a heart running along the upper (dorsal) part of the body and a nerve cord running along the lower (ventral) part of the body; and

— symmetrical construction of both sides of the animal (bilateral symmetry).

In the manner in which all life forms are organized and classified, the primary subdivisions of a phylum, such as Arthropoda, are known as classes. Although this book concerns itself primarily with the class Insecta, the insects, representatives of six other arthropod classes may be found in yards and gardens: springtails, arachnids, millipedes, centipedes, symphylans, and some land-adapted crustaceans (e.g., sowbugs, pillbugs).

There are a few additional groups of animals included in this book, notably the slugs and snails. These are mollusks, phylum Mollusca, more closely related to clams and mussels than insects, but often perceived as being "garden bugs" and may produce injuries similar to those of many insects. Two other phyla are given a bit of attention in chapter 6, the segmented worms, phylum Annelida, which includes earthworms, and the flatworms, phylum Platyhelminthes.

The classification of the animals described in this book, to the order level, is summarized as follows:

Phylum ARTHOPODAArthropods

Class MALACOSTRACA

Order Isopoda Pillbugs and Sowbugs

Order Decapoda Crayfish, Shrimp

Order Amphipoda Amphipods

Class DIPLOPODA Millipedes

Order Julida

Order Spirobolida

Order Polydesmida Flat-backed millipedes

Order Polyxenida Bristly millipedes

Class CHILOPODA Centipedes

Order Lithobiomorpha Stone centipedes

Order Scolopendromorpha Bark centipedes

Order Geophilomorpha Soil centipedes

Order Scutigeridae House centipedes

Class SYMPHYLA Symphylans

Order Scutigerellidae Symphylans

Class ARACHNIDA Arachnids

Order Opiliones Daddy longlegs, Harvestmen

Order Araneae Spiders

Order Acari Mites and Ticks

Class COLLEMBOLA Springtails

Class INSECTA Insects

Phylum MOLLUSCAMollusks

Class GASTROPODA Gastropods

Clade: Stylommatophora Slugs and Snails

Phylum ANNELIDASegmented Worms

Class CLITELLATA Leeches and Earthworms

Subclass Oligochaeta Earthworms

Phylum PLATYHELMINTHESFlatworms, Flukes, Tapeworms

Class TERBELLARIA Free-living Flatworms

ARTHROPOD GROWTH AND METAMORPHOSIS

Because arthropods possess an external skeleton, which confines their size, in order to grow they must periodically shed the exoskeleton, building a new, larger one at the same time. This process is called molting and all arthropods must molt repeatedly during their lifetime. As a result of this type of development, arthropod growth occurs in a series of distinct stages, each punctuated by a molting event. The term instar is used to describe each of the stages in a developing arthropod; insects typically pass through three to seven instars as they develop. The ultimate stage is the sexually mature adult.

During this growth process, arthropods will not only progressively increase in size but usually also undergo some changes in form, a process known as metamorphosis. Sometimes these changes are minor, perhaps involving small differences in body shape, coloration, or patterning. In others there can be dramatic differences in appearance during different stages in their development.

Broadly speaking, among the insects, one of two general patterns of metamorphosis is followed: simple metamorphosis or complete metamorphosis. Earwigs, grasshoppers, and aphids are examples of those that have a simple type of metamorphosis. They have immature stages, known as nymphs, that generally resemble the adult in overall appearance, feed in the same manner, and occur in the same environments. In addition to a change in size, the nymphs may develop external features, such as wing pads, that become increasingly prominent in later instars. Adult insects differ from nymphs by being sexually mature and, if they are winged, having functional wings. Much more specialization of function — and difference in form — occur among the insects that undergo complete metamorphosis. The immature stages are collectively known as larvae, although larvae of many insects are so recognizable that they may be referred to by a common name such as grub, caterpillar, or maggot. Immature forms are often similar in appearance, progressively increasing in size with each instar. Following is transition to a unique stage known as the pupa. Tremendous changes take place during the pupal stage as larval features disappear and transition to features unique to the adult — the transformation of a caterpillar to a butterfly being one of the best recognized examples. Among insects with complete metamorphosis, the appearance and habits of the adult may be very different from those of larvae. The overwhelming number of insect species are those that undergo complete metamorphosis and include beetles, moths and butterflies, flies, bees, ants, and wasps.

Regardless of the type of metamorphosis, further development of external structures ceases once insects molt to their ultimate adult form. Therefore a little fly is not a "baby" big fly nor is a tiny ant a "baby" ant. They are merely adults of a small species or individuals that were stressed through poor diet or some other factor that suppressed development in their immature stages.

There are variations in this development pattern among some insects and the noninsect arthropods. Springtails and insects that evolved before the development of wings, such as silverfish (order Thysanura), show little change in form as they grow, but gradually increase in size and become sexually mature in the ultimate stages. Most arachnids (spiders, mites, scorpions, and the like) have a development pattern similar to simple metamorphosis. However, among the mites and ticks, the first-instar nymphs that emerge from eggs have only six legs, obtaining their full complement of eight legs only after the next molt (second instar). Among all millipedes and many centipedes, additional leg-bearing segments will be added during some molts, resulting in a type of growth known as anamorphic development.

INSECT ORDERS

Several features separate insects from the other arthropod classes. These include:

— division of the body into three main regions (head, thorax, abdomen);

— three pairs of legs, located on the thorax; and

— one pair of antennae.

Many insects also develop wings in the adult stage and thus are the only winged arthropods.

Currently, about 30 orders of insects are recognized. Several are infrequently, if ever, encountered in North American yards and gardens because of their small size, scarcity, or habits that restrict them to different environments. The orders and types of metamorphosis of the insects most likely to be seen in yards and gardens include:

IDENTIFICATION OF IMMATURE STAGES OF ARTHROPODS

Because of the changes that occur during development, arthropods change in appearance at different life stages. These changes are particularly dramatic in insects that undergo complete metamorphosis (e.g., beetles, moths and butterflies, bees, ants, wasps, and flies). Often it is the immature stage (e.g., caterpillar, grub) that causes most plant injury, as many larvae are specialized feeding machines. Adults may feed in a very different way and have very different form and functions (e.g., reproduction, dispersal); thus, it can be particularly difficult when observing insects that have complete metamorphosis to associate the adult and immature stages as being the same species.

The arthropod orders with immature stages most likely to be seen in yards and gardens are discussed below.

COLEOPTERA (BEETLES)

Beetle larvae are often known as grubs. All possess strong jaws designed to chew, and the jaws may be quite prominent in species that chew wood or capture prey. Three pairs of legs on the thorax are clearly present among those species that actively move about aboveground or on the surface of plants (e.g., lady beetles, leaf beetles).

Grubs that develop belowground or within plants typically lose pigmentation and are pale colored, usually creamy white. Among those that actively dig in soil, such as the white grubs, the front legs are well developed and may be used in digging. Many important groups of beetles develop within plants, however, and their larvae have lost all legs in the course of evolution, leaving only the darkly colored head capsule as a conspicuous feature. The larvae of bark beetles and weevils somewhat resemble pieces of puffed rice with a dark head. Flat-headed borers, the larvae of metallic wood borers, are quite elongated and have a broad area on the first segment of the thorax. Roundheaded borers, larvae of longhorned beetles, are also quite elongated, with the dark prominent jaws distinguishing the head region.

LEPIDOPTERA (BUTTERFLIES, MOTHS, SKIPPERS)

Immature stages of lepidopterans are known as caterpillars. They possess the normal three pairs of true legs on the thorax but, unlike most immature insects, they also possess fleshy leglike extensions, known as prolegs, on several segments of the abdomen. Each proleg is tipped with minute hooks, known as crochets, arranged in patterns characteristic of each family. All lepidopteran caterpillars can be distinguished from other insect larvae by the presence of two to five pairs of prolegs, each of which is tipped with crochets.

The legs and prolegs of caterpillars that bore into plants (e.g., clearwing borers) may be very reduced; however, the presence of crochets always distinguishes them from other wood-boring larvae.

NEUROPTERA (LACEWINGS, ANTLIONS, AND RELATIVES)

All neuropteran larvae are predators. Curved, lancelike jaws project prominently from the head. Larvae possess legs on the thorax but no prolegs on the abdomen.

HYMENOPTERA (ANTS, BEES, WASPS, SAWFLIES, AND RELATIVES)

Rarely do gardeners encounter the larval stages of most insects in the order Hymenoptera. This is because they either occur within colonies (e.g., social wasps, honey bees, ants), develop in specialized nest cells (e.g., hunting wasps, leafcutter bees), or are hidden within plants (e.g., gall wasps). These larvae are usually very pale-colored and have little pigmentation except around the mouthparts. A distinct head region is present but can be difficult to distinguish since there is little difference in color to distinguish it from the rest of the body.

Larval features are very different among some of the active leaf-feeding larvae, notably the sawflies. Sawfly larvae look quite similar to moth and butterfly larvae and similarly are often termed caterpillars. Like Lepidoptera larvae, sawfly larvae have prolegs on the abdomen, but the number is significantly different. Sawflies possess six to eight pairs of prolegs, and none have the hooklike crochets at the tip that characterize moth and butterfly larvae.

DIPTERA (FLIES, GNATS, MOSQUITOES, AND RELATIVES)

Larvae of the "true flies" completely lack legs. Furthermore, many lack any distinct head area. Instead the head end is often tapered to a point and surrounds a pair of tiny hooks that are normally retracted. A pair of eyelike spiracles are commonly present on the hind end. This larval form is known as a maggot and is produced by flies in the suborder Brachycera (e.g., root maggots, house flies, flower flies).

Larvae in the suborder Nematocera (e.g., gnats, midges, mosquitoes) also lack legs but have a distinctly visible head capsule that is often darker than the rest of the body.

ORTHOPTERA (GRASSHOPPERS, CRICKETS, KATYDIDS)

Most features of immature and adult Orthoptera are similar. Only the adult has fully developed wings, however. Coloration and patterning among nymphs also commonly change with age. Wing pads are present on immature stages and become more prominent as maturity approaches.

DERMAPTERA (EARWIGS)

Most features of immature and adult earwigs are similar. The forceps-like cerci on the tip of the abdomen and the wing pads increase in size as the insects mature.

MANTODEA (MANTIDS)

Mantids are recognized by their raptorial (grasping) front legs. Most external features of immature and adult mantids are similar except for the wings. As mantids develop, the wing pads become increasingly prominent, with the wings becoming fully developed and functional only in the adult stage.

BLATTODEA (COCKROACHES AND TERMITES)

Most external features of immature and adult cockroaches are similar except for the wings. As cockroaches develop, the wing pads become increasingly prominent, with the wings becoming fully developed and functional only in the adult stage.

Features of almost all immature and adult termites are similar, differing only in size. However, termites are social species and metamorphosis patterns are more flexible, allowing the production of various castes (e.g., workers, soldiers, reproductives) as colony needs determine. Reproductive forms possess large, functional wings in the adult stage and distinct wing buds in the early stages of development. Workers and soldiers are blind and not or only lightly pigmented. Winged reproductives have eyes and are often black or brown.

THYSANOPTERA (THRIPS)

Most immature thrips roughly resemble adults in general body form, and the first two nymphal instars often are found together with the adults on plants. However, immature thrips lack wings and often have different coloration. Late stages (instars 3 and 4) usually drop to the soil and undergo physical changes, such as development of wing pads, which make them progressively similar to the ultimate adult form.

HEMIPTERA (TRUE BUGS, APHIDS, PSYLLIDS, WHITEFLIES, SCALE INSECTS, CICADAS, LEAFHOPPERS, AND RELATIVES)

The order Hemiptera contains a large number of insects that all possess "piercing-sucking" mouthparts of similar design that allow them to pierce tissues (usually plant tissues) and suck fluids. All have a simple type of metamorphosis, and thus immature stages (nymphs) feed in a manner similar to the adults and share many other habits with them. Body form is generally similar, but nymphs lack the fully developed wings of the adults and are not sexually mature. Wing pads become increasingly prominent as the nymphs approach maturity.

In some families, however, there can be unusual forms. In whiteflies and psyllids, nymphs are quite flattened and look very different from the winged adults. This is particularly true in whiteflies where there is a special nonfeeding transition stage (sometimes referred to as a pupa) immediately preceding the adult. The first stage following egg hatch among scale insects, known as the crawler, is highly mobile and little resembles the more sedentary later stages that produce a waxy cover. Similarly, the nymphs of cicadas are specialized for life belowground, whereas adults are winged and look substantially different.

ODONATA (DAMSELFLIES AND DRAGONFLIES)

Immature stages of dragonflies and damselflies develop in water and will not be encountered in a yard/garden setting, except sites with permanent water features. Their appearance is much different from their ultimate adult form, being wingless, often much more squat in body form, and possessing a unique modification of the mouthparts: an extensible "lower jaw" (labium) that is used to help capture insects and other prey. When full grown, the nymphs migrate to the edges of ponds or onto emergent vegetation, rocks, or other surfaces then molt to the adult stage.

COLLEMBOLA (SPRINGTAILS)

All stages of springtails have similar external features and differ only in size. Unlike insects, springtails will continue to molt after they have reached the adult stage.

(Continues…)

---

Excerpted from "Garden Insects of North America"
by .
Copyright © 2018 Princeton University Press.
Excerpted by permission of PRINCETON UNIVERSITY PRESS.
All rights reserved. No part of this excerpt may be reproduced or reprinted without permission in writing from the publisher.
Excerpts are provided by Dial-A-Book Inc. solely for the personal use of visitors to this web site.

---