When you want to identify an insect the first step is to find out in which Order it is classified. For this you can use a dichotomous key. A dichotomous key is a tool that uses paired statements or questions to guide you to the solution.
To use the key, start at the top and compare statements 1a and 1b. Select the statement that describes your insect specimen and continue with the number indicated on the right (click the number to jump to the next statement).
Identification keys are a good starting point, but you should realize that there are hundred thousands of insect species in this world and among them there is a lot of variation. The keys cannot cover all this variation. When you have reached a solution, always double check the result by reading a detailed description of the insect Order.
| 1a | Insect with wings (but the forewings could be partly or entirely stiffened as ‘wing-covers’ or ‘wing-cases’ and are not used for flying) |
2 |
| 1b | Insect without wings (but there could be remnants of wings resembling small scales or pads) |
32 |
| 2a | Insect with one pair of wings | 3 |
| 2b | Insect with two pairs of wings | 9 |
| 3a | The dorsal surface of the prothorax extends backwards over the abdomen; the hind-legs enlarged and modified for jumping; insect looks grasshopper-like in general appearance | Orthoptera |
| 3b | Insect different | 4 |
| 4a | The wings are horny or leathery (stiff or rigid) and are not used for flying | 5 |
| 4b | The wings are membranous (flexible) and are used for flying | 6 |
| 5a | The wings overlap at least a little in the centre-line and with obvious veins present | Phasmida |
| 5b | The wings (elytra) meet in the centre-line (sometimes they are fused together) and without veins (note that the elytra may have longitudinal grooves or striae but these should not be confused with veins) | Coleoptera |
| 6a | The abdomen has one or more long terminal appendages | 7 |
| 6b | The abdomen is without terminal appendages | 8 |
| 7a | The wings have only one forked vein; antennae are relatively long; small insect usually less than 5 mm long | Hemiptera |
| 7b | The wings have many veins; antennae are short; larger insect | Ephemeroptera |
| 8a | The thorax has a pair of club-shaped structures (halteres) situated just in front of the wings | Strepsiptera |
| 8b | The thorax has a pair of club-shaped structures (halteres) lying just behind the wings (these halteres may be hidden by body hairs and other structures) | Diptera |
| 9a | The forewings are partly or entirely horny or leathery and form stiffened covers for the membranous hindwings | 10 |
| 9b | Both pairs of wings are membranous (flexible) and used for flying (sometimes the wings are feather-like rather than membranous or their membranous nature may be obscured by a covering of hairs, scales or waxy powder) | 16 |
| 10a | The mouth-parts form a tube-like ‘beak’ (rostrum) which is used for piercing and sucking (this rostrum is usually folded backwards under the body when not in use) | Hemiptera |
| 10b | The mouth-parts have jaws (mandibles) and are designed for biting and chewing | 11 |
| 11a | The forewings overlap at least a little in the centre-line and usually with many veins present | 12 |
| 11b | The forewings (elytra) meet in the centre-line and have no veins (note that the elytra may have longitudinal grooves or striae but these should not be confused with veins) | 14 |
| 12a | The hind-legs are enlarged and modified for jumping; insect looks like a grasshopper in general appearance | Orthoptera |
| 12b | The hind-legs are not modified for jumping and are usually similar in thickness to the middle-legs; insect is not grasshopper-like | 13 |
| 13a | The prothorax is much larger than the head; cerci nearly always many-segmented and fairly prominent | Dictyoptera |
| 13b | Prothorax and head are of similar size; cerci are not segmented and very short | Phasmida |
| 14a | The forewings (elytra) are long and cover all or most of the abdomen | Coleoptera |
| 14b | The forewings (elytra) are short and much of the abdomen remains exposed | 15 |
| 15a | The abdomen has a pair of terminal pincers or forceps | Dermaptera |
| 15b | The abdomen has no terminal pincers | Coleoptera |
| 16a | The wings are very narrow without veins and fringed with long hairs (feather-like); tarsi are 1- or 2-segmented; small slender insect often found in flowers | Thysanoptera |
| 16b | The wings broader with veins present; if wings are fringed with long hairs then tarsi are comprised of more than 2 segments (the wing veins of some insects may be much reduced and hardly visible or partly obscured by hairs, scales or waxy powder) | 17 |
| 17a | The hindwings are clearly smaller than the forewings | 18 |
| 17b | Both pairs of wings are similar in size or hindwings larger than forewings | 26 |
| 18a | Wings and much of the body covered with white waxy powder; tiny insect usually less than 2-3 mm long | 19 |
| 18b | Without powdery covering | 20 |
| 19a | When at rest the wings are held flat over the body; the mouth-parts form a tube-like ‘beak’ (rostrum) for piercing and sucking (this rostrum is usually folded backwards under the body when not in use) | Hemiptera |
| 19b | When at rest the wings are held roof-wise over the body; the mouth-parts have jaws (mandibles) and are designed for biting | Neuroptera |
| 20a | The wings are more or less covered with very small scales; the mouth-parts when present are forming a coiled proboscis or ‘tongue’ | Lepidoptera |
| 20b | The wings are usually transparent (wings without scales but often hairy); the mouth-parts are not forming a coiled proboscis | 21 |
| 21a | The forewings have many cross-veins making a network pattern; the abdomen has 2 or 3 long thread-like terminal appendages | Ephemeroptera |
| 21b | The forewings show relatively few cross-veins; the abdomen is usually without or with only very short terminal appendages (cerci) | 22 |
| 22a | The wings are noticeably covered with hairs; insect looks moth-like in general appearance | Trichoptera |
| 22b | The wings are not noticeably hairy (but wings may be fringed with hairs or tiny surface hairs may be seen if wings are inspected under a microscope or strong hand-lens) | 23 |
| 23a | The mouth-parts form a tube-like ‘beak’ (rostrum) for piercing and sucking (usually the rostrum is folded backwards under the body when not in use; the abdomen sometimes has tubular outgrowths or cornicles near the hind end) | Hemiptera |
| 23b | The mouth-parts has jaws (mandibles) and are designed for biting and chewing | 24 |
| 24a | The tarsi are 4- or 5-segmented; hard-bodied insects with the abdomen often constricted at its base into a petiole or narrow ‘waist’ | Hymenoptera |
| 24b | The tarsi are 2- or 3-segmented; small soft-bodied insect | 25 |
| 25a | Antennae with at least 12 segments | Psocoptera |
| 25b | Antennae with only 9 segments | Zoraptera |
| 26a | The tarsi are 5-segmented | 27 |
| 26b | The tarsi are 3- or 4-segmented | 29 |
| 27a | The wings are noticeably covered with hairs; insect is moth-like in general appearance | Trichoptera |
| 27b | The wings are not noticeably hairy (but tiny hairs may be seen if the wings are observed under a microscope or with a strong hand-lens) | 28 |
| 28a | The front of the head is extended downwards to form a beak-like structure with jaws (mandibles) at its tip | Mecoptera |
| 28b | Insect without such a beak-like extension of the head | Neuroptera |
| 29a | The tarsi are 4-segmented | Isoptera |
| 29b | The tarsi are 3-segmented | 30 |
| 30a | The wings are noticeably hairy; the front tarsi are with the first segment greatly swollen | Embioptera |
| 30b | The wings are not noticeably hairy; the front tarsi are simple | 31 |
| 31a | The wings have many cross-veins, which makes a network pattern; wings are held away from the body at rest (either outstretched or folded vertically); the antennae are short and inconspicuous | Odonata |
| 31b | The wings have relatively few cross-veins and are folded flat over the body when at rest; the antennae are long and slender (longer than the width of the head) | Plecoptera |
| 32a | Small soft-bodied insect which lives on terrestrial plants with the body encased under a protective shield (‘scale’) or the body is partly covered with white waxy filaments or powder | Hemiptera |
| 32b | Insect different | 33 |
| 33a | Thoracic legs are absent or enclosed in a membrane preventing any movement | (Larvae and pupae of most Orders of Endopterygota) |
| 33b | Thoracic legs are present and fully functional | 34 |
| 34a | The abdomen has false-legs or prolegs (prolegs are fleshy leg-like structures that are different from and additional to the jointed legs of the thorax); the insect looks like a caterpillar in general appearance | 35 |
| 34b | The abdomen has no prolegs; the insect is not caterpillar-like in appearance | 37 |
| 35a | Abdomen with not more than 5 pairs of prolegs | Lepidoptera |
| 35b | Abdomen has at least 6 pairs of prolegs | 36 |
| 36a | The head has a single small eye (ocellus) on each side | Larvae of Hymenoptera |
| 36b | The head has several small eyes (ocelli) on each side | Larvae of Mecoptera |
| 37a | The insect lives in a terrestrial habitat or on the surface of water (not underwater) | 38 |
| 37b | The insect is truly aquatic (living underwater) | 70 |
| 38a | The abdomen has cerci or other terminal appendages (but be careful not to confuse terminal hairs or bristles with cerci) | 39 |
| 38b | The abdomen does not have such terminal appendages (but it may have small appendages on proximal segments or a pair of tubular outgrowths or cornicles near the hind end) | 56 |
| 39a | The abdomen has 6 or fewer segments; usually the abdomen has a forked terminal appendage (springing organ) folded under the rear end when not in use | Collembola |
| 39b | The abdomen has more than 6 segments (usually 8 or more are clearly visible); the terminal appendages are of a different form | 40 |
| 40a | The antennae are short and often inconspicuous (the same length as the head or shorter) | 41 |
| 40b | The antennae are long and conspicuous (usually they are much longer than the head) | 42 |
| 41a | The tarsi have at least 3 segments (usually they are 5-segmented) | Phasmida |
| 41b | The tarsi have fewer than 3 segments (often they are reduced to single or paired claws on the end of each leg) | Larvae of Coleoptera |
| 42a | The hind-legs are enlarged and modified for jumping; insect looks like a grasshopper in general appearance | Orthoptera |
| 42b | The hind-legs are not modified for jumping; usually the hind-legs are similar in thickness to the middle-legs; insect does not look grasshopper-like | 43 |
| 43a | The terminal appendages of the abdomen form a pair of pincers or forceps | 44 |
| 43b | The terminal appendages of the abdomen are different | 45 |
| 44a | The tarsi are 3-segmented | Dermaptera |
| 44b | The tarsi are 1-segmented | Diplura |
| 45a | The terminal appendages of the abdomen are long (much more than half the length of the abdomen) | 46 |
| 45b | The terminal appendages of the abdomen are short (less than half the length of the abdomen) | 48 |
| 46a | The abdomen has 3 terminal appendages (these are a paired cerci and a median filament) | Thysanura |
| 46b | The abdomen has only 2 terminal appendages (cerci) | 47 |
| 47a | The tarsi are 3-segmented; the terminal appendages of the abdomen (cerci) are unsegmented | Dermaptera |
| 47b | The tarsi are 1-segmented; the terminal appendages of the abdomen (cerci) are many-segmented | Diplura |
| 48a | The tarsi are usually 5-segmented (but sometimes fewer on regenerated legs of Phasmida) | 49 |
| 48b | The tarsi have fewer than 5 segments on all legs | 52 |
| 49a | The front of the head is extended downwards to form a beak-like structure with jaws (mandibles) at its tip | Mecoptera |
| 49b | Insect without such a beak-like extension of the head | 50 |
| 50a | The prothorax is much larger than the head | Dictyoptera |
| 50b | The prothorax and head are of similar size (the prothorax is at most only a little bit larger than the head) | 51 |
| 51a | The cerci are 8-segmented and are moderately long | Grylloblattodea |
| 51b | The cerci are unsegmented and are very short | Phasmida |
| 52a | The tarsi are usually 4-segmented | Isoptera |
| 52b | The tarsi have fewer than 4 segments | 53 |
| 53a | The tarsi are 1-segmented | Diplura |
| 53b | The tarsi are 2- or 3-segmented | 54 |
| 54a | The tarsi are 2-segmented | Zoraptera |
| 54b | The tarsi are 3-segmented | 55 |
| 55a | The front tarsi have a first segment which is greatly swollen; the cerci are 2-segmented | Embioptera |
| 55b | The front tarsi are not swollen; the cerci are unsegmented | Phasmida |
| 56a | The insect lives as a parasite on a warm-blooded animal or it is closely associated with such an animal (for example it lives on the body or in the nest or den of a bird or mammal) | 57 |
| 56b | The insect is not parasitic on a warm-blooded animal | 61 |
| 57a | The insect body is flattened from side to side; jumping insect | Siphonaptera |
| 57b | The insect body is flattened from top to bottom | 58 |
| 58a | The head is partly withdrawn into the thorax | 59 |
| 58b | The head is not withdrawn into the thorax | 60 |
| 59a | The antennae are short and inconspicuous (they are much shorter than the head); legs with strong and distinctly hooked tarsal claws | Diptera |
| 59b | The antennae are long and conspicuous (they are more than twice the length of the head); legs have small and only slightly curved tarsal claws | Hemiptera |
| 60a | At least the prothorax is distinct from the other thoracic segments; the legs have small tarsal claws; the mouth-parts have jaws (mandibles) and are designed for biting | Mallophaga |
| 60b | All the thoracic segments are fused into a single unit; the legs have large tarsal claws which can close tightly against the legs; the mouth-parts form a tube-like proboscis for piercing and sucking (this proboscis is retracted within the head when not in use) | Siphunculata |
| 61a | Insect without antennae (very small soil-living insects usually less than 2 mm long) | Protura |
| 61b | Antennae are present | 62 |
| 62a | The abdomen is strongly constricted at its base into a narrow petiole or ‘waist’; the antennae are often bent into an elbowed shape | Hymenoptera |
| 62b | The abdomen is not constricted into a ‘waist’; the antennae are more or less straight | 63 |
| 63a | The body is covered with dense scales and flattened hairs | Lepidoptera |
| 63b | The body is bare or with sparse bristle-like hairs | 64 |
| 64a | The mouth-parts form a tube-like proboscis or rostrum for piercing and/or sucking (this proboscis is usually folded backwards under the head when not in use) | 65 |
| 64b | The mouth-parts are with jaws (mandibles) and designed for biting and/or chewing | 67 |
| 65a | The tarsi are usually 5-segmented | Diptera |
| 65b | The tarsi have fewer than 5 segments | 66 |
| 66a | The proboscis is small and cone shaped (it is much shorter in length than the head) (small slender insect often found in flowers) | Thysanoptera |
| 66b | The proboscis or rostrum is long and jointed (it is nearly always longer than the head) (abdomen sometimes with tubular outgrowths or cornicles near the hind end) | Hemiptera |
| 67a | The antennae are short and often inconspicuous (length of the antennae is at most about the same length as the head) | 68 |
| 67b | The antennae are long and conspicuous (they are much longer than the head) | 69 |
| 68a | The abdomen has 6 or fewer segments | Collembola |
| 68b | The abdomen has more than 6 segments (usually 8 or more segments are clearly visible) | (Larvae of various Orders) |
| 69a | The head is narrower than the body; the mandibles are very long and protruding forward well in front of the head (the mandibles are clearly visible from above) | Larvae of Neuroptera |
| 69b | The head is as wide or nearly as wide as the body; the mandibles are small and not protruding in front of the head (they are not visible from above) | Psocoptera |
| 70a | The mouth-parts with a tube-like ‘beak’ or with long stylets and are designed for piercing and sucking | 71 |
| 70b | The mouth-parts have jaws (mandibles) and are designed for biting and/or chewing | 72 |
| 71a | The mouth-parts form a robust tube-like ‘beak’ (rostrum) folded backwards under the body when not in use | Hemiptera |
| 71b | The mouth-parts form a pair of long and slender stylets extending more or less straight forward in front of the head between the antennae and about as long or longer than the antennae | Larvae of Neuroptera |
| 72a | Head has a hinged grasping organ (or ‘mask’) that can stick out; this organ bears large terminal claws (normally it is folded beneath the head when not in use) | Nymphs of Odonata |
| 72b | No hinged grasping organ or ‘mask’ beneath the head | 73 |
| 73a | The abdomen has pairs of feather-like or flat plate-like lateral appendages on some segments (gill filaments) and 3 long terminal appendages (paired cerci and a median filament) | Nymphs of Ephemeroptera |
| 73b | Insects without this combination of features | 74 |
| 74a | The abdomen is without lateral appendages but with 2 long terminal appendages (cerci); the antennae are long and slender (they are much longer than the head) | Nymphs of Plecoptera |
| 74b | Insects without this combination of features | 75 |
| 75a | The abdomen has pairs of multi-jointed feather-like lateral appendages on some segments (gill filaments) and sometimes a single terminal appendage | Larvae of Neuroptera |
| 75b | The abdomen is without lateral appendages (gill filaments) or if such appendages are present then they are always unjointed | 76 |
| 76a | The last abdominal segment has a pair of fleshy appendages each bearing a strong claw; the middle- and hind-legs are longer than the width of the thorax; the body is often enclosed in a tubular case made from small pebbles or other debris | Larvae of Trichoptera |
| 76b | Insects without this combination of features | Larvae of Coleoptera |
For technical terms, please see the Glossary of Entomology