Tips: Only adult arthropods are included, and certain uncommon orders are not included. To use a key, read both descriptions in a couplet (for instance, 1a and 1b). Decide which sounds most like your critter, and move to the next couplet indicated. Should you reach a dead-end, use the numbers in parentheses to backtrack until you reach a couplet that you felt unsure about, and try following the other path. Some orders are found more than once in the keys, because the arthropods occur in different forms.

STEP	FROM	CHARACTERS	ORDER / CLASS
1a		Does not resemble a twig. . . . . . . . . . go to 2
1b		Slow-moving, resembles a twig	PHASMIDA (Walking sticks)
2a	1a	Body very soft. . . . . . . . . . go to 3
2b	1a	Body not exceptionally soft. . . . . . . . . . go to 8
3a	2a	Mouthparts hidden within head, usually with a springlike structure (furcula) on the underside of the abdomen used for jumping	COLLEMBOLA (Springtails)
3b	2a	External mouthparts, without a springlike structure on the underside of the abdomen. . . . . . . . . . go to 4
4a	3b	Visible projections at the tip of the abdomen. . . . . . . . . . go to 5
4b	3b	No visible projections at the tip of the abdomen. . . . . . . . . . go to 6
5a	4a	Long flattened body, tip of abdomen with 2 - 3 long tails (cerci, and if a third tail is present, a median caudal filament)	THYSANURA (Silverfish)
5b	4a	Small pear-shaped body, tip of abdomen has two short projections (cornicles), some individuals have wings	HOMOPTERA (Aphids)
6a	4b	Usually found in colonies with many individuals (soldier caste), some of which have very large heads and mandibles (soldier caste) or mouthparts that look like a tube (nasuti caste)	ISOPTERA (Termites)
6b	4b	Tiny insects that may be found in groups of many individuals, but they all have the same kind of mouthparts . . . . . . . . . . go to 7
7a	6b	Chewing mouthparts, relatively long antennae, when individuals have wings the wings never have fringes of hair	PSOCOPTERA (Bark lice)
7b	6b	Sucking mouthparts, fairly short antennae, adults may actually have barely visible wings with fringes of hair	THYSANOPTERA (Thrips)
8a	2b	Body with a narrow "waist," antennae usually have a bend in the middle	HYMENOPTERA (Ants & Wingless wasps)
8b	2b	Body without a narrow "waist", antennae don't usually have a bend in the middle. . . . . . . . . . go to 9
9a	8b	Tiny jumping parasites found on mammals or birds, where they suck blood	SIPHONAPTERA (Fleas)
9b	8b	Not found on mammals or birds, chewing mouthparts. . . . . . . . . . go to 10
10a	9b	Prominent "pincers" at the tip of the abdomen (cerci)	DERMAPTERA (Earwigs)
10b	9b	Without "pincers" at the tip of the abdomen	COLEOPTERA (Beetles)

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