2-D says, “Finally! You got here. Here’s where all my relatives and I fit in. There are more of us than of you, so that makes us really important. We insects live pretty-much everywhere on earth except out, deep in the ocean, but our cousins the Crustacea have that covered.”
Phylum Arthropoda (arthro = joint; poda = foot) is the most numerous phylum of all living organisms, both in number of species and in number of individuals. One, very conservative, estimate is that there are well over one million species of insects alone. In terms of number of individuals, there are more ants than anything else, and in terms of numbers of species, there are more kinds of beetles than anything else: 40 to 50% of all insect species are beetles. There are more species of insects than all other plants and animals together.
Molting Cicada
An arthropod has a segmented body covered by an exoskeleton
made from chitin and other chemicals. This exoskeleton serves as
protection and provides places for muscle attachment. Arthropods must molt
because their exoskeletons don’t grow with them. Arthropods have open
circulatory systems consisting of a dorsal heart which collects blood from
the body cavity and pumps it back into the body cavity again. In insects,
the anterior portion of the heart (which is located in the abdomen) is
extended into a tube that is called an aorta which directs the blood forward
as it goes out into the body cavity. Arthropods have a well-developed,
mesodermal, ventral, solid nerve cord and well-developed sense organs.
The body feature from which the phylum takes its name is the jointed
appendages, which include antennae and mouthparts as well as walking
legs.
It is thought that the early arthropod ancestors (descended from organisms that looked like marine worms or, later, Peripatus) looked sort of like a centipede: they had a number of body segments, each with a pair of jointed appendages. From there, some of these segments became fused to form a head and some of the appendages became modified to form mouthparts or antennae. Early on, there was an evolutionary split which led to the various modern subphyla and classes. Currently, three living subphyla are recognized, with trilobites representing an extinct fourth subphylum.
Earthworm-like Ancestor
↓
Clamworm-like Ancestor
↓
Peripatus-like Ancestor
↓
Various Arthropods
Generic Arachnid:
Generic Crustacean:
Generic Insect:
Class example(s) |
Number of antennae |
Number of legs & attachment |
Number of body parts & attachment |
Photo |
---|---|---|---|---|
Subphylum Trilobitomorpha | ||||
Class Trilobita trilobites |
These were most common during the Cambrian and Ordovician periods of geological history, and can be found preserved in a number of rock formations in the Cincinnati area. They are now extinct. | |||
Subphylum Chelicerata | ||||
Class Merostomata horseshoe crabs |
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Class Arachnida
spiders scorpions mites ticks daddy-long-legs |
0 | 4 prs, att. to cephalothorax, (chelicerae & pedipalps are m.p.) | cephalothorax & abdomen | |
Class Pycnogonida sea spiders |
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Subphylum Crustacea | ||||
Class Malacostraca crayfish crabs pillbugs etc. |
2 pair | 5 prs incl. cheliped att. to cephalothorax, and swimmerets, m.p., incl. mandibles | cephalothorax & abdomen | |
Note: there are quite a number of other classes of Crustacea not listed here. | ||||
Subphylum Atelocerata | ||||
Class Diplopoda millipedes |
1 pair | many, 2 pr per apparent segment bec of fused segm., m.p. incl. mandibles | head and “trunk” segments, every two segments fused into one apparent segment | |
Class Chilopoda
centipedes |
1 pair | many, 1 pr per segment, m.p. incl. mandibles & poison claw on next segm. | head and “trunk” segments | |
Class Pauropoda pauropods |
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Class Symphyla symphylans |
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Class Hexapoda (Insecta)
insects |
1 pair | 3 pr, 1 pr. per thoracic segment, m.p. incl mandibles, some abdominal | head, three-segmented thorax, segmented abdomen (wings are not appendages) |
Some further notes on various subgroups within Arthropoda:
Gradual Metamorphosis
Complete Metamorphosis
This list only includes some of the more common insect orders. There are other, less common ones that have been left off the list.
Order example(s) |
Type of Front Wing | Type of Back Wing | Other Notes | Photo |
---|---|---|---|---|
Subclass Entognatha | ||||
(endo, ento = within, inner; gnatho = the jaw), mouthparts within the head, primarily wingless, simple metamorphosis, no longer considered to be insects | ||||
Collembola springtail |
none | none | (coll = glue; embola = a bolt or wedge) — collophore on bottom of 1st abdominal segm., for water uptake + furcula = jumping organ on ventral abdomen | |
Subclass Insecta | ||||
(ecto = outside, out, outer) ectognathous — mouthparts stick out from head | ||||
Apterygota | ||||
(a- = not, without; ptero = wing, feather) primarily wingless, simple metamorphosis | ||||
Thysanura silverfish firebrats |
none | none | (thysan = fringe) — somewhat flattened body, three taillike structures on posterior end, body often covered with scales | |
Pterygota | ||||
winged (a few are secondarily wingless) | ||||
Exopterygota | ||||
(exo
= out, outside) — gradual metamorphosis, wing pads develop externally,
young are called nymphs (naiads if aquatic) — Ephemeroptera, Odonata, and Plecoptera, which have aquatic naiads, are said to be hemimetabolous (hemi = half). |
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Ephemeroptera mayflies |
membranous | membranous, smaller than front wings | (ephemer = for a day, temporary) — aquatic naiads, winged subimago, then adult; very short-lived as adults | |
Odonata dragonfly damselfly |
membranous long & narrow |
membranous long & narrow |
(odonto = tooth) — have “teeth” on mandibles, aquatic naiads; chewing mp; long & slender | |
Phasmida walkingstick leaf insect |
leathery tegmina (or absent) |
membranous (or absent) |
(phasmato = apparition, phantom) — chewing mp; look like sticks or leaves, & well-camouflaged | |
Orthoptera grasshopper katydid camel cricket cricket |
leathery tegmina (or absent) |
membranous (or absent) |
(ortho = straight) — jumping back legs; chewing mouthparts | |
Mantodea mantis |
leathery tegmina (or absent) |
membranous (or absent) |
(manti, mantid, mantis = a soothsayer, a kind of grasshopper) — chewing mp; front legs adapted for catching prey | |
Blattaria cockroach |
leathery tegmina (or absent) |
membranous (or absent) |
(blatta = cockroach) — chewing mp; legs adapted for running | |
Isoptera termite |
membranous (or absent) |
membranous; same size as front (or absent) | (iso = equal) — light-colored; no “waist”; chewing mp; small size; social with castes, winged reproductives; | |
Dermaptera earwig |
shortened = brachypterous
(or absent); leathery, called tegmina or elytra |
membranous; folded under front wings (or absent) | (derm = skin) — forceps-like cerci at end of abdomen | |
Plecoptera stoneflies |
membranous | membranous, “bottom” area folded under at rest | (pleco = twine, twist, braid, twisted, folded) — aquatic naiads | |
Phthiraptera lice Suborder Mallophaga chewing lice; Suborder Anoplura sucking lice |
none | none | (phthir = lice) — ectoparasites (mostly on birds or mammals) | |
Hemiptera true bug |
half-leathery, half-membranous hemelytra; “X” when folded |
membranous | (hemi = half) — piercing-sucking mp; | |
Homoptera leafhopper cicada aphid scale insect |
membranous (or absent) |
membranous (or absent) |
(homo = same, like, alike) — piercing-sucking mp | |
similar to each other (unlike true bugs), held rooflike or tentlike over body when at rest | ||||
Endopterygota | ||||
(endo = within, inner) — complete metamorphosis, wing pads develop internally until pupal stage, young called larvae |
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Neuroptera dobsonfly lacewing antlion |
membranous | membranous | (neuro = nerve, sinew, cord)
— named for wing veins; dobsonfly larvae are aquatic; many prey
on other insects (Photo © D.B. Fankhauser) |
|
Coleoptera beetle |
hard, shell-like elytra | membranous | (coleo = a sheath) — chewing mouthparts; largest order with ~40% of all insects | |
Mecoptera scorpionfly |
membranous | membranous | (meco = long, length) — tip of male’s abdomen curls up, resembling shape of scorpion’s (photo is female); long, snout-like head | |
Siphonaptera flea |
none | none | (siphon = tube, pipe) — pupa in cocoon; blood-sucking; jumping; small & flat | |
Diptera fly mosquito cranefly gnat |
membranous | modified as halteres | (di = two) — adults with sponging, cutting-sponging, or piercing-sucking mp | |
Lepidoptera butterfly skipper moth |
bright color due to scales | bright color due to scales | (lepido = a scale) — siphoning mp in adults, chewing in larvae (caterpillar) | |
Hymenoptera bee ant wasp |
membranous (or absent) |
membranous, smaller than front (or absent) |
(hymeno = a membrane) — have a “waist”; chewing mp; many can sting; many social in colonies; often black & yellow bodies |
Some further notes on various subgroups within Arthropoda:
In the table, above, roaches, mantids, and walkingsticks are each listed as being in their own orders (Blattaria, Mantodea, and Phasmida, respectively), but you will also find that those three orders are frequently combined in one order, Order Dictyoptera (you may even run across some really-old entomology book that puts all of these into Order Orthoptera).
These are similar to orthopterans, but without jumping legs. They also have leathery tegmina. The forelegs of mantids are adapted for capturing prey. Many mantids and walkingsticks are well camouflaged, resembling sticks, leaves, or flowers.Talk about confusing taxonomy! This is it! Most entomologists these days use “Hemiptera” and the following order, “Homoptera,” but over the years, those names and “Heteroptera” (hetero = other, different) have “flip-flopped” back and forth. I’ve seen “Order Heteroptera” containing “Suborders Hemiptera and Homoptera,” as well as “Order Hemiptera” containing “Suborders Heteroptera and Homoptera,” while still other people don’t even use “Hemiptera” at all, preferring to use just “Heteroptera” instead.
2-D says, “Here I am! Here I am! Hurray, you finally found me. I’m so glad you’re here! If you have time, check out the pictures and information from when Ms. Carter’s General Biology Lab class raised Monarchs for an international research project.”
Butterflies and moths use the “ZW” system of sex determination: females are heterogametic or ZW and males are homogametic or ZZ. Thus, the sex of the offspring is determined by the type of egg (Z or W) which the mother produces, not by the father’s sperm which are all Z.Try to match an insect picture with the name of the order in which that insect belongs. Click on two squares. OK... Javascript weirdness... it wouldn’t show the second picture clicked before “turning them back over.” So, I got that fixed – sort-of. It will now display the first two pictures clicked, then when you click on a third one, it will go back and check the first two. I know, that makes it easy to lose track of whether you’re on a “first” or “second” click, but eventually you should be able to get to the end of it. When you click anywhere on the squares after you match the last pair, the pictures will reload in a different order so you can try again.