how to know an insect

How To Know an Insect

What Kind of Insect Is It?

C. F. W. Muesebeck

The Animal Kingdom is made up of a number of major divisions, or phyla.

One of them, the Ghordata, includes man and the other mammals, birds, reptiles, fish—in fact, all the verte- brates, the creatures that have back- bones.

By far the largest division from the standpoint of the number of different kinds, or species, it comprises is the Arthropoda. At least 80 percent of all known animals are arthropods. This phylum comprises invertebrate (back- boneless) animals that have a segmented body, jointed appendages, and a hard outer covering, or exoskeleton. It is in turn divided into a number of groups called classes, each of which differs in some fundamental characteristics from the others. One of these classes, known as Hexapoda, or In- secta, contains all the insects. Various members of other classes of Arthro- poda, especially such organisms as mites, ticks, spiders, scorpions, millipedes, centipedes, and sowbugs, however, are so commonly regarded as insects that it seems advisable to indicate the basic distinctions between these several classes in a simple key.

A key is based on the process of ^ elimination. In the key that follows,

for example, one considers ( as in entry number i ) the number of legs of the creature he wishes to identify. If it has five or more pairs, he consults entry 2 (as given at the right) ; if it has three or four pairs, he skips to entry 4. And so on.

Key to the Principal Classes of Arthropoda

1. With five or more pairs of legs 2 With three or four pairs of legs 4

2. Body wormlike; head not merged with the thorax and provided with one pair of antennae or with none 3

Body not wormlike; head merged with the thorax and provided with two pairs of antennae

Crustacea (crabs, lobsters, shrimp, sowbugs, etc.) (figure I, next page)

3. Body segments each with only one pair of legs ^

Chilopoda (centipedes') (figure

Most of the body segments each with two pairs of legs

Diplopoda (millipedes) (figure 3) ....

4. Body composed of two main divisions, the céphalothorax (fused head and thorax) and abdomen; four pairs of jointed legs; wings and antennae lacking

Arachnida (spiders (figure 4), scorpions (figure 5), mites, ticks, etc.)

Body composed of three main divisions, the head, thorax, and abdomen; only three pairs of jointed legs; wings usually, antennae always, present

Insecta (all insects)

For purposes of orderly classification and to facilitate identification, each of these classes is divided into a number of orders, an order is broken down into families, a family is divided into genera, and each genus is comDosed of related

43

44 Yearbook of Agriculture 1952

Millipede.

Centipede.

Scorpion.

Spider,

*# •"■■fS

MHB ^^9^ .^^^^H^^l

J^^^^^^^^^^^^^EE^E^ß^^^'' % ''^^^l

^^^^^^^^^Hi'

aj^^ Ûy^^H

^HL ^■H ' ^1

A froghopper producing its protecting mass of bubbles. Within, it is sheltered from the direct rays of the sun and kept moist by the foam.

The lacewing is one of the polecats of the insect world. It exudes u disagreeable smelling fluid when it is touched.

After 17 years of tunneling in the darkness of the earth, a periodical cicada nymph begins transforming into the adult cicada.

é A carpenter ant obtaining honejtlL-w iiDm the nymphs t)l the treehoppei, Eníylia shiuata.

One of the American walkingstick insects. In the Tropics, such insects assume their largest and their oddest forms.

The dragonlly. 1 ht- nymphs of these insects live under water and are equipped with extensible lower lips that can shoot out to grasp prey.

\\\ xY

V If w- % r'^<

'«J; ^♦♦♦♦♦•♦v S' I'V*.

,^'

Face of a robber fly, which sometimes feigns death to escape its enemies. The foregoing photographs are by Edwin Way Teale. (See page 8.)

This dragonfly, preserved in the limestone of Solnhofen, Bavaria, lived millions of years ago. (See page 14.)


species. Thousands of species of insects have thus far been described. Obvi- ously each species must have a distinct name, and because many species are cosmopoHtan the same name must be used for the same species everywhere. When the present system of naming animals was established about 200 years ago, most scientific books were written in Latin, and Latin was con- sidered the universal language of science. The scientific names of animals, therefore, are in Latin or in Latin form. The name of each species con- sists of two w^ords, the name of the genus to which the species belongs and a word, often an adjective, that stands for the species.

The generic name begins with a capital letter; the specific (i. e., the species) name is written in lower case and may be followed by the name, or an abbreviation of the name, of the person who originally proposed the scientific name and described the species. Thus, the name of the house fly is written Musca domestica L. The "L." is an abbreviation for Carolus Linnaeus, the Swedish scientist who described this species.

Under the International Rules of Zoological Nomenclature, a generic name may not be duplicated anywhere in the animal kingdom. The same specific name may be used repeatedly but only for one species in any one genus. The rules assure a distinctive name for each kind, or species, of animal and make it possible to record information about any species under a designation that will be universally understood.

As si-iowN in the foregoing key to the major classes of arthropods, insects have only three pairs of legs, never more. This is the most distinctive char- acteristic of the class Insecta. Insects also have three separate body divisions, head, thorax, and abdomen. There is always one pair of antennae.

Wings are usually present. When they occur, wings alone will serve im- mediately to identify an arthropod as an insect, for they are found in no

070134°—52 5

45 Other class of this phylum. Many insects, however, are wingless. In all the major orders, some wingless forms occur. In a few of the smaller orders, such as the Thysanura (silverfish), Collembola (springtails), Siphonap- tera (fleas), Mallophaga (biting lice), and Anoplura (sucking lice), all the species are wingless. The winged or wingless condition, the texture or covering of the wings, their shape, their number (whether two or four), the manner in which they are held when at rest, and the peculiarities of their system of veins furnish characters that help one recognize a given insect as belonging to a particular order. Examples of wings of different kinds are noted in the sketches of insects that are used to illustrate the key to the principal insect groups. Other structures, in which significant differ- ences occur that are useful in the defi- nition of orders or families, are the mouth parts and the antennae.

For the identification of genera, and eventually of species, a great array of characteristics must be studied, includ- ing minute details of sculpture, ar- rangements of hairs or bristles, shape and proportional measurements of various parts of the body and appendages, and even details of the reproductive organs that can be demonstrated only by preparation on microscope slides after dissection. Details of every kind that tend to be distinctive of group or species need to be used and the range of variation in all of them must be determined.

Many of the insects commonly col- lected or observed doing damage are in the immature stages. During this pe- riod they may bear no resemblance whatever to the adults of the same species. The members of the Orthop- tera (grasshoppers, roaches, crickets, mantids) and the Hemiptera (bugs), am.ong others, develop by gradual change after hatching from the eggs, and the young are similar in general form to the adults, differing principally in size and in the lack of wings. The young of other large orders, however.


Ocellus

HEAD} PROTHORAX

Antenna

Foreleg Middle leg

such as the Coleóptera (beetles), Díp- tera (flies), Lepidoptera (moths and butterflies) and Hymenoptera (saw- flics, bees, wasps, and ants), are whofly unUke the adults. The eggs hatch into larvae, some of which are commonly called grubs, maggots, or caterpillars. These represent the feeding stage, during which all growth occurs. When de- velopment is complete, the larva changes into a pupa, which is the rest- ing, inactive stage, and then the re- markable transformation to the adult insect takes place. Most of the commonly encountered larvae belong to the four orders just mentioned and may be distinguished by the following characteristics :

Hind leg

The larvae of moths and butterflies have a pair of jointed legs on each of the first three body segments and, in addition, short, fleshy, un jointed legs (called prolegs) on some of the other segments. The head is distinctly set off.

Beetle larvae resemble those of the moths and butterflies in usually hav- ing a pair of jointed legs on each of the first three body segments and also in the distinct head, but they are at once distinguished by lacking prolegs.

The maggots of flics arc completely legless, the body tapers noticeably toward the anterior end, and the head is usually not distinctly set ofT from the rest of the body.

Larvae of sawflies (a section of the

What Kind of Insect Is It? order Hymenoptera) are often mis- taken for those of moths and butterflies because they are provided with both jointed legs and prolcgs and are found in similar situations, but they may be recognized by the presence on each side of the head of a dark-colored eyespot, which is lacking in larvae of the other group. They also arc usually not hairy whereas larvae of Lepidoptera are often conspicuously so.

Adult insects^ even those of the same order^ often differ so much in appear- ance that they are not thought to be related, and it is impossible to construct a key by which every insect may be cor-

47 rectly placed. The simplified key that follows, however, will aid one with lit- tle knowledge of insects to recognize the more common types in the adult stage. Often even such group recogni- tion will suffice to indicate what should be done in a practical case that seems to demand prompt action. It should be easily possible^ for example, for any- one with no entomological training to distinguish an ant from a termite. Most persons consider termites to be a type of ant, distinguishable only by an expert, but actually termites and ants belong in widely separated orders and structurally are quite unlike.

3.

Key to Major Groups Containing Common Insects

Wings present, the front wings often 4. Wings with a network of veins, in- in the form of hard, leathery or eluding many cross veins .... horny, wing covers 2 Order Ephemcroptera (may-

Wings absent or represented only by flics), in part (figure 6, be- minute pads 43 low)

With only one pair of wings, these Wings with very few longitudinal always membranous 3 veins and no cross veins ....

With two pairs of wings, the front Hemiptera, in part (males of pair often represented by hard scale insects or Goccidae) v/ing covers beneath which the 5- Antenna very short, usually three- hind wings are concealed in re- segmented, the last segment the pose . . 8 longest and provided with a con-

End of abdomen with two or three spicuous, long bristle or with a slender but conspicuous, back- number of rings or annulations . . wardly projecting filaments ... 4 Antenna longer and composed of

End of abdomen without such fila- many segments; body generally ments slender; wings narrow

Order Diptcra (mosquitoes, (Midges, crane flies, mosqui- midges, flies) 5 ^°^^) (^^^^^ 7)

Mosquito.

Yearbook of Agriculture 1952

Horse fly,

6. Last segment of antenna ringed or annulated and without a conspicuous long bristle (arista) at base

(Bee flies, robber flies, horse flies) (figure 8)

Last segment of antenna with a long bristle (arista) on upper side at base . 7

7. Calypter (scalclike structure behind base of wing) large and conspicuous; mcsonotal suture complete; larger flies

Calyptcratc Muscoidea (house flies, blow flies, flesh flics and their relatives) (figure 9)

Calypter small and inconspicuous; mcsonotal suture incomplete ; mostly small flies, much smaller than house fly

Acalypterate Muscoidea (eye gnats, pomace or vinegar flies, fruit flies ) ( figure i o )

8. Front wings horny, rigid, opaque, without veins, meeting in a line over middle of body and conceal- ing the membranous hind wings . 9

Front wings usually membranous

I Blow fly. Pomace fly.

although often covered with scales or hairs; if leathery, with the veins distinct, and not meeting along a line over middle of body 16

9. Tip of abdomen with a pair of prominent forceps-like appendages; front wings (wing covers) very short

Order Dermaptcra (earwigs) (figure 11 )

Tip of abdomen without such appendages; front wings (wing covers) usually covering most or all of abdomen although sometimes short

Order Coleóptera (beetles) . IO 10. Front of head produced into a

beak Family Curculionidae (wee-

vils) (figure 12) Front of head not produced into a

beak 11 11. Wing covers very short, leaving last

five or more of the abdominal segments exposed

Family Staphylinidae (rove beetles) (figure 13)

Weevil. Rove beetle.

Earwig.

What Kind of Insect Is It? A9

Lady beetle. Larder beetle.

May beetle.

Wing covers extending to or near tip of abdomen, rarely leaving three segments exposed 12

12. Antennae enlarged toward tips ... 13 Antennae not enlarged toward tips,

slender, sometimes longer than the body 15

13. Antennae lamellate (segments com- posing the club in the form of ieaflike plates)

Family Scarabaeidae (May beetles, Japanese beetle, rose chafer, etc.) (figure 14)

Antennae not lamellate 14 14. Tarsi apparently three-segmented .

Family Coccinellidae (lady beetles) (figure 15)

Tarsi four-segmented Family Dermestidae (larder

beetles, carpet beetles) (figure 16)

15. Tarsi five-segmented, the third segment not enlarged; antennae much shorter than body

Family Carabidae (ground beetles) (figure 17)

Tarsi apparently four-segmented, the third segment greatly en-

larged and deeply cleft conceal- ing the very small fourth segment ; antennae usually longer than body

Family Gerambycidae (longhorned beetles) (figure 18)

16. Front wings more or less leathery or parchment-like 17

Wings membranous 23 17. Mouth parts in the form of a pierc-

ing and sucking beak Order Hemiptera, in part . . 18

Mouth parts fitted for chewing . . . Order Orthoptera 19

18. Front wings leathery only at base, the apical third or more ab- ruptly membranous and overlapping; beak arising from front part of head

Suborder Heteroptera (true bugs) (figure 19)

Front wings of same thickness throughout and usually sloping rooflikc over the body

Suborder Homoptera, in part (leafhoppers and their allies) (figure 20)

Ground beetle.

Stink bug.

Longhorned beetle.


Leafhopper.

Cockroach.

Praying marxtid.

Cricket. Grasshopper. Katydid.

19, All legs slender, similar in form; body flattened from above . . .

Family Blattidae (roaches) (figure 21 )

Either the front legs or the hind legs greatly modified and very different in form from the others . . .

20. Front legs greatly enlarged and spined, fitted for seizing and hold- ing prey; prothorax slender, in form of a long neck; head broad and capable of unusually free movement

Family Mantidae (mantids) (figure 22)

Front legs normal; hind legs fitted for jumping, the femora much enlarged 21

21. Antennae short, much shorter than body

Family Acrididae (grasshoppers) (figure 23)

Antennae longer than the body . . 22 22. Tarsi four-segmented

Family Locustidae (long- . horned grasshoppers, katy- dids, etc.) (figure 24)

Tarsi three-segmented Family Gryllidae (crickets)

(figure 25)

What Kind of Insect Is It? ¡23. Wings covered with minute over-

lapping scales, often in beautiful color patterns

Order Lepidoptera (moths and butterflies) 24

Wings not covered with scales ... 26 24. Antennae usually threadlike or

feathery, not enlarged at tips; wings, in repose, held rooflike over body; body very hairy. Mostly night-flying insects . . .

Suborder Heterocera (moths) (figure 26)

Antennae enlarged at tips; wings, in repose, usually held in a vertical position, or the forewings erect and the hind wings more or less horizontal; body not especially hairy. Mostly day-flying ....

Suborder Rhopalocera (butterflies and skippers) .... 25

25. Extreme tips of antennae recurved or hooked

Family Hesperiidae (skippers) (figure 27)

Extreme tips of antennae knobbed . Family Papilionidae and allies

(butterflies) (figure 28) 26. Wings very narrow, bladelike and

fringed with long bristles; tarsus ending in a large bladderlike structure

Order Thysanoptera (thrips) (figure 29)

Wings not bladelike ; tarsus without such a bladderlike structure ... 27

27. Mouth parts in the form of a beak fitted for piercing and sucking . .

Hemiptera, in part 28 Mouth parts fitted for chewing ... 29

28. Front wings lacelike, horizontal and overlapping in repose; small, flattened insects

Family Tingidae (lace bugs) (figure 30)

Front wings not lacelike, usually sloping and not overlapping in repose

Families Cicadidae (cicadas) (figure 31 ), Aphidae (plant- lice) (figure 32), and their relatives

Skipper.

Butterfly.

Cicada.


Aphid. Termite.

36 \

Stoneiîy.

29. Wings with numerous longitudinal vrins and many cross veins form- ing a networii 30

Wings with few cross veins and usually with few longitudinal veins, not net-veined 35

30. Antennae very short and inconspicuous, composed of few segments , 31

Antennae conspicuous, composed of many segments 33

31. Hind wings very small ; tip of abdomen with two or three long filaments extending backward . . .

Order Ephemeroptera, in part (mayflies)

Front and hind wings of about equal size: abdomen without terminal filaments

Order Odonata 32 32. Front and hind wings similar in

shape, slender at bases; wings, in repose, held in a vertical posi-

Dragonfly. Lacewing.

tion over abdomen Suborder Zoraptera (damsel-

flies) (figure 33) Hind wing much broadened at base;

wings, in repose, horizontal, ex- tended outward

Suborder Anisoptera (dragon- flies) (figure 34)

33. Wing veins mostly membranous and faint: front and hind wings of same size and shape; tarsi four- segmented

Order Isoptera (termites) (figure 35, winged form)

Wing veins strongly developed . . . 34. Tarsi two- or three-segmented . . .

Order Plecoptera (stoneflies) (figure 36)

Tarsi five-segmented Order Ncuroptera (lacewings

(figure 37) dobsonflics (figure 38), etc.)

34


Caddisfly.

Dobsonfly.

Chalcidfly. Ant.

35. Tarsi five-segmented 36 38. Tarsi two- or three-segmented . . .

Order Corrodentia (psocids) 36. Wings covered with fine long hair

and held rooflike over abdomen, in response

Order Trichoptera (caddis- flies) (figure 39)

Wings transparent, not covered with long hairs, not held rooflike over abdomen in repose 39.

Order Hymenoptera 37 37. Abdomen broadly joined to the

thorax Suborder Symphyta (sawflies,

wood wasps) (figure 40) Abdomen more or less constricted

at base 38

Petiole of abdomen (basal part by which abdomen is attached to thorax) composed of a single vertical platelike segment or of two narrow segments that are conspicuously set off from the re- mainder of the abdomen

Family Formicidae (ants) (figure 41, winged form)

Petiole of abdomen not as above . . 39 Front wing without a stigma (a

more or less triangular, opaque, often discolored spot behind middle of front margin)

Superfamily Ghalcidoidea, etc. (chalcidflies and their relatives) (figure 42)

Front wing with a stigma 40

54

Honey bee.

^v ^ \ Hornet.

Yearbook of Agriculture 1952 40. Body hairy^ the hairs branched; first

segment of tarsus often greatly broadened and fitted for gather- ing pollen

Superfamily Apoidca (bees) (figure 43)

Body usually not so hairy, the hairs not branched 41

41. Wings folded lengthwise when in repose

Family Vespidae (wasps and hornets) (figure 44)

Wings not folded lengthwise when in repose 42

42. Antennae usually long and slender, composed of many segments; female usually with a projecting ovipositor

Superfamily Ichneumonoidea (ichneumonflies) (figure 45)

Ichneumonfly. Silverfish.

What Kind of Insect Is It? Antennae short, composed of 12 or

13 segments; female without a projecting ovipositor

Superfamily Sphecoidea (thread-waisted wasps) (figure 46 )

43. Tip of abdomen with two or three long appendages directed backward 44.

Tip of abdomen without such appendages 45

44. Abdominal appendages thick, rigid, in the form of forceps

Order Dcrmaptcra, in part ( earwigs )

Abdominal appendages delicate, flexible, antenna-like

Order Thysanura (silverfish, etc.) (figure 47)

45. Tarsus composed of only one to three segments 46

Tarsus composed of four or five segments 50

46. Antennae conspicuous, projecting in front of head 47

Antennae very short, inconspicuous, not projecting in front of head . 49

47. Antennae composed of three to six segments 48

Antennae with more than six seg- rnents ; very tiny insects that sometimes occur by the thousands in damp houses

Corrodentia fpsocids) (figure 48)

48. Mouth parts in the form of a distinct beak; body greatly flattened

Order Hemiptera, Family Gi- micidae (bed bugs) (figure 49)

Mouth parts not in the form of a beak; body not flattened ....

Order Gollerabola (springtails) (figure 50)

49. With biting mouth parts Order Mallophaga (biting

lice) (figure 51) ^ With piercing and sucking mouth

parts Order Anoplura (sucking lice)

(figure 52) 50. Antennae prominent 51

Antennae inconspicuous, not projecting^ 52

51. Body noticeably constricted at base of abdomen, antennae elbowed, the basal segment very long; tarsus five-segmented

Order Hymenoptera, Family Formicidae (ants) (figure 53, wingless form)

Body not constricted at base of abdomen; antennae not elbowed, basal segment short; tarsus four- segmented

Order Isoptcra (termites) (figure 54, wingless form)

Termite.

52. Body strongly compressed from the sides; abdomen distinctly segmented; coxae very large and strongly flattened; legs fitted for jumpmg

Order (fleas) Siphonaptera (figure 55)

Body not compressed ; abdomen not distinctly segmented; legs not fitted for jumping

Order Díptera, in part; wingless forms (sheep-tick and its relatives)

how to know an insect

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