Identifying an opportunist: identification keys
You can start from the animal you see or from the damage on the host (plant, animal, hive), including diseases caused by fungi, oomycetes, bacteria, phytoplasmas and viruses. The questions only concern visible shapes and signs; each answer comes with a diagram. The key leads to a group, then to the opportunists on this site that belong to it.
Colour and size are never used: they vary with age, food, climate and the individual.
Warning: the associations between recipes and opportunists come from other references (traditional practices, publications, user feedback). They are neither a recommendation nor a claim of effectiveness. There is no certainty regarding the preparation, application and use of these bio-preparations. See the regulations
Answer the questions while looking at the organism (a ×10 hand lens helps). If unsure, click “I don't know”: the key will show every possibility in that branch.
The key's groups, arranged by branch. Each drawing leads to the group's sheet.
Beetles (others)Adult (and nymphs resembling the adult) · 11
WeevilsAdult (and nymphs resembling the adult) · 9
Scarabs (chafers, rhinoceros beetles…)Adult (and nymphs resembling the adult) · 2
Shield bugs and true bugsAdult (and nymphs resembling the adult) · 2
Grasshoppers, locusts and cricketsAdult (and nymphs resembling the adult) · 0
Butterflies and mothsAdult (and nymphs resembling the adult) · 28
ThripsAdult (and nymphs resembling the adult) · 3
Ants, wasps and gall waspsAdult (and nymphs resembling the adult) · 3
Leafhoppers, planthoppers and psyllids (jumpers)Adult (and nymphs resembling the adult) · 3
Aphids and phylloxeraAdult (and nymphs resembling the adult) · 3
WhitefliesAdult (and nymphs resembling the adult) · 1
Powdery mildew (fungi)Damage and symptoms on the host · 2
Downy mildew and late blight (oomycetes)Damage and symptoms on the host · 9
Rusts (fungi)Damage and symptoms on the host · 6
Leaf spots and scabs (fungi)Damage and symptoms on the host · 18
Bacterial diseasesDamage and symptoms on the host · 4
Rots with mould (fungi and oomycetes)Damage and symptoms on the host · 7
Trunk and branch cankersDamage and symptoms on the host · 6
Vascular wilts (fungi and bacteria of the vessels)Damage and symptoms on the host · 5
Viral diseasesDamage and symptoms on the host · 9
Phytoplasmas and phloem bacteriaDamage and symptoms on the host · 3
Leaf curl and blisters caused by fungiDamage and symptoms on the host · 1
Swollen or galled roots (protists, nematodes)Damage and symptoms on the host · 3
Root and collar rotsDamage and symptoms on the host · 2
Diseased ears and grains (bunts, Fusarium head blight)Damage and symptoms on the host · 2
The same organism changes shape during its life. In complete metamorphosis, the larva does not look like the adult and goes through a motionless stage (pupa or chrysalis). In incomplete metamorphosis, the nymphs look like the adult, without wings or with wing buds.
| Larva | Intermediate stage | Adult | Metamorphosis |
|---|---|---|---|
    Scarabaeiform, elateriform, leaf-beetle or legless larva |
Motionless pupa with free appendages, in soil or plant | Beetles (others) |
|
     Caterpillar (leaf-eating, looper, miner, borer, hairy) |
Chrysalis with appendages glued to the body, sometimes in a silk cocoon | Butterflies and moths |
|
 Maggot with no head or legs |
Puparium: the last larval skin hardens into a barrel |  Flies (brachyceran Diptera) |
|
 Legless larva or sawfly larva |
Pupa, often in a cell or cocoon | Ants, wasps and gall wasps |
|
| Wingless larva resembling the adult | Motionless prepupa and pupa, often in the soil | Thrips |
|
| Wingless nymphs resembling the adult | Nymphs with wing buds (no motionless stage) | Shield bugs and true bugs |
|
| Wingless nymphs resembling the adult | Nymphs with wing buds, already jumping | Leafhoppers, planthoppers and psyllids (jumpers) |
|
| Nymphs resembling the adult, often born live | Winged or wingless nymphs (no motionless stage) | Aphids and phylloxera |
|
| Mobile crawler that settles at once and becomes a flat scale | Motionless “pupa” under the leaf | Whiteflies |
|
| Young mobile crawlers looking for a spot | Settled nymphs forming their shield or wax |  Scale insects and mealybugs |
|
| Wingless nymphs resembling the adult | Nymphs with wing buds | Grasshoppers, locusts and crickets |
|
| Larva with 3 pairs of legs | Nymphs with 4 pairs of legs |  Mites |
The body parts used in the keys.
All the questions as a tree, with the diagram for each answer.
Slugs and snails (molluscs)
Nematodes
Flukes (flatworms)Maggot (fly larva)Legless larva with a head (weevils, seed beetles, bark beetles, wasps)Shield bugs and true bugsLeafhoppers, planthoppers and psyllids (jumpers)Aphids and phylloxeraWhitefliesGrasshoppers, locusts and cricketsThripsFlies (brachyceran Diptera)
Midges and gnats (nematoceran Diptera)Scale insects and mealybugsWeevilsScarabs (chafers, rhinoceros beetles…)Beetles (others)Shield bugs and true bugsGrasshoppers, locusts and cricketsButterflies and mothsThripsWhitefliesLeafhoppers, planthoppers and psyllids (jumpers)Aphids and phylloxeraAnts, wasps and gall waspsLooper caterpillar (geometrids and allies)Leaf-mining caterpillarBoring caterpillar (fruits, stems, cobs, tubers, wood)Hairy caterpillar (processionary and allies)Leaf-eating caterpillarSawfly larva (false caterpillar)Scarabaeiform larva (white grub)Elateriform larva (wireworm)
Campodeiform larva (ground and rove beetles, lacewings, ladybirds)Leaf beetle larva and alliesAphids and phylloxeraShield bugs and true bugsLeafhoppers, planthoppers and psyllids (jumpers)Ants, wasps and gall wasps
Lice and other wingless animal parasitesThripsGrasshoppers, locusts and cricketsScale insects and mealybugs
Symphylans and other myriapodsSlugs and snails (molluscs)Leaf-eating caterpillarLeaf-mining caterpillarBeetles (others)WeevilsPowdery mildew (fungi)Downy mildew and late blight (oomycetes)Rusts (fungi)Rots with mould (fungi and oomycetes)Aphids and phylloxeraWhitefliesScale insects and mealybugsLeafhoppers, planthoppers and psyllids (jumpers)Leaf spots and scabs (fungi)Bacterial diseasesViral diseasesLeaf curl and blisters caused by fungiAnts, wasps and gall waspsAphids and phylloxeraMitesMidges and gnats (nematoceran Diptera)Aphids and phylloxeraWhitefliesScale insects and mealybugsLeafhoppers, planthoppers and psyllids (jumpers)Viral diseasesPhytoplasmas and phloem bacteriaRots with mould (fungi and oomycetes)Boring caterpillar (fruits, stems, cobs, tubers, wood)Legless larva with a head (weevils, seed beetles, bark beetles, wasps)Maggot (fly larva)Leaf spots and scabs (fungi)Viral diseasesDiseased ears and grains (bunts, Fusarium head blight)Trunk and branch cankersBoring caterpillar (fruits, stems, cobs, tubers, wood)Legless larva with a head (weevils, seed beetles, bark beetles, wasps)Maggot (fly larva)Scale insects and mealybugsBacterial diseasesVascular wilts (fungi and bacteria of the vessels)Swollen or galled roots (protists, nematodes)Root and collar rotsScarabaeiform larva (white grub)Elateriform larva (wireworm)Maggot (fly larva)Symphylans and other myriapodsLeaf beetle larva and alliesVascular wilts (fungi and bacteria of the vessels)Viral diseasesPhytoplasmas and phloem bacteriaSwollen or galled roots (protists, nematodes)Root and collar rotsScarabaeiform larva (white grub)Elateriform larva (wireworm)Maggot (fly larva)Symphylans and other myriapodsLeaf beetle larva and alliesMitesShield bugs and true bugsLeafhoppers, planthoppers and psyllids (jumpers)Aphids and phylloxeraWhitefliesGrasshoppers, locusts and cricketsThripsFlies (brachyceran Diptera)Midges and gnats (nematoceran Diptera)Scale insects and mealybugsWeevilsScarabs (chafers, rhinoceros beetles…)Beetles (others)Shield bugs and true bugsGrasshoppers, locusts and cricketsButterflies and mothsThripsWhitefliesLeafhoppers, planthoppers and psyllids (jumpers)Aphids and phylloxeraAnts, wasps and gall waspsLooper caterpillar (geometrids and allies)Leaf-mining caterpillarBoring caterpillar (fruits, stems, cobs, tubers, wood)Hairy caterpillar (processionary and allies)Leaf-eating caterpillarSawfly larva (false caterpillar)Scarabaeiform larva (white grub)Elateriform larva (wireworm)Campodeiform larva (ground and rove beetles, lacewings, ladybirds)Leaf beetle larva and alliesAphids and phylloxeraShield bugs and true bugsLeafhoppers, planthoppers and psyllids (jumpers)Ants, wasps and gall waspsLice and other wingless animal parasitesThripsGrasshoppers, locusts and cricketsScale insects and mealybugsSymphylans and other myriapodsMaggot (fly larva)
Internal parasites of livestock and bees
Damaged brood and combs (hive)
How to recognise it : Soft, slimy body with no legs or segments, moving on a muscular foot; two pairs of tentacles on the head, eyes at the tip of the upper pair; snails carry a coiled shell. They leave slime trails.
How to recognise it : Worms with a cylindrical, smooth, unsegmented body tapering at both ends, with no legs or distinct head. On plants they are mostly spotted through their symptoms (root galls or cysts, decline) and by laboratory analysis; in animals they live in the gut or lungs.
Barber's pole worm Cattle lungworm Golden potato cyst nematode Pine wood nematode Poultry roundworm Root-knot nematodes
How to recognise it : Flattened, leaf-shaped worms with no segments or legs and two suckers at the front; they live in the liver of ruminants. Their cycle passes through an aquatic snail of wet areas.
How to recognise it : One-piece body with no waist, antennae or wings; 4 pairs of legs in the adult (3 in the larva; only 2 pairs, at the front of an elongated body, in eriophyid mites). The mouthparts do not form a projecting “head”. They give themselves away by fine webbing, discoloration, galls or, on animals, crusts and itching.
Itch mite (Sarcoptes) Litchi erinose mite Mites Poultry red mite Sheep scab mite (Psoroptes) Spider mite Varroa mite
How to recognise it : Mites whose mouthparts form a clearly visible “false head” (capitulum) at the front, bearing a toothed harpoon; a hard dorsal shield in hard ticks; 4 pairs of legs. They stay attached to an animal's skin for several days.
How to recognise it : Elongated body made of many nearly identical segments, with more than 7 pairs of legs and one pair of antennae. Symphylans run quickly through the soil and eat fine roots.
How to recognise it : No legs and no head capsule: the front end is pointed and bears two hardened mouth hooks; the rear end is blunt, with two breathing plates. Lives inside fruits, roots, bulbs or stems, or in animals' wounds and body cavities.
Carrot fly Cattle warble fly (Hypoderma) Common green bottle fly (sheep strike) Housefly Mediterranean fruit fly Melon fly Narcissus bulb fly Olive fruit fly Onion fly Sheep bot fly Spotted wing drosophila Walnut husk fly
How to recognise it : No legs, but a hard, clearly distinct head capsule with mandibles; soft, wrinkled, C-shaped body. Lives hidden inside a seed, fruit, stem, wood, root or gall.
Annona seed borer 
Banana weevil Bean weevil Coffee berry borer Groundnut bruchid Hazelnut weevil Mango seed weevil Pea leaf weevil Pea weevil Red palm weevil Strawberry blossom weevil Tamarind weevil Weevil
How to recognise it : 3 pairs of jointed legs behind the head and fleshy prolegs on the abdomen tipped with a ring of hooks. Usually 5 pairs of prolegs. Lives in the open or in leaves rolled or tied with silk and gnaws the leaf blade.
Box tree moth Caterpillars / worms Fall armyworm Large white butterfly Quinoa moth
How to recognise it : 3 pairs of jointed legs behind the head and fleshy prolegs on the abdomen tipped with a ring of hooks. Only 2 or 3 pairs of prolegs, all at the rear: it moves by looping its body.
How to recognise it : Lives inside the leaf between its two skins, digging a tunnel (mine) visible against the light; flattened body with reduced legs and prolegs. Some fly larvae also mine leaves but have no head or legs.
Caterpillars / worms Citrus leafminer Coffee leaf miner Leek moth Olive moth Potato tuber moth Tomato leafminer
How to recognise it : 3 pairs of jointed legs behind the head and fleshy prolegs on the abdomen tipped with a ring of hooks. Lives inside a fruit, stem, cob, tuber or wood; it gives itself away by an entry hole, sawdust or frass coming out of the tunnel.
Annona fruit borer Cactus moth Caterpillars / worms Cocoa pod borer Codling moth Cotton bollworm (Helicoverpa) Eggplant fruit and shoot borer European corn borer European grapevine moth False codling moth Greater wax moth Litchi fruit borer Macadamia nut borer Olive moth Oriental fruit moth Palm borer moth Pink bollworm Potato tuber moth Quinoa moth Sugarcane borer
How to recognise it : 3 pairs of jointed legs behind the head and fleshy prolegs on the abdomen tipped with a ring of hooks. The body is covered with setae or tufts of hairs, often stinging; they live in groups, in silk nests or in lines.
Caterpillars / worms Oak processionary moth Pine processionary
How to recognise it : Looks like a caterpillar but has 6 or more pairs of prolegs without hooks and a single simple eye on each side of the head. Often feeds in groups from the leaf edge.
No opportunist on this site is linked to this group yet.
How to recognise it : Fleshy, soft, C-shaped body; hard head capsule and 3 well-formed pairs of legs; the tip of the abdomen is swollen and translucent. Lives in soil, compost or rotting wood and gnaws roots.
Beetles Coconut rhinoceros beetle Common cockchafer (white grub)
How to recognise it : Cylindrical, straight, hard body with smooth, uniform segments; 3 pairs of legs behind the head; the last segment is often pointed or notched. Lives in the soil and bores into roots, tubers and seeds.
How to recognise it : Elongated, soft, often humped body with tubercles, warts or spines; distinct head and 3 pairs of legs; no prolegs and no cerci at the end. Lives in the open on leaves or in the soil near roots.
Beetles Colorado potato beetle Crucifer flea beetle Eucalyptus snout beetle Pollen beetle Rosemary beetle Small hive beetle Western corn rootworm
How to recognise it : Elongated, flattened body, running legs, prominent mandibles, often two appendages (cerci) at the tip of the abdomen; very active. Most hunt other insects: they are usually beneficials, not opportunists.
No opportunist on this site is linked to this group yet.
How to recognise it : Forewings turned into hard, veinless elytra meeting in a straight line down the middle of the back and covering the folded hind wings; chewing mouthparts; thread-like, toothed or compact-clubbed antennae, no snout.
Bean weevil Beetles Coffee berry borer Colorado potato beetle Crucifer flea beetle Groundnut bruchid Pea weevil Pollen beetle Rosemary beetle Small hive beetle Western corn rootworm
How to recognise it : Beetles whose head extends into a snout (rostrum) with the mouth at its tip; elbowed antennae attached to the rostrum and ending in a club.
Banana weevil Eucalyptus snout beetle Hazelnut weevil Mango seed weevil Pea leaf weevil Red palm weevil Strawberry blossom weevil Tamarind weevil Weevil
How to recognise it : Stout, domed beetles whose antennae end in a club of movable plates that open like a fan; front legs often toothed for digging. Their larvae are scarabaeiform white grubs.
How to recognise it : Jointed piercing beak arising from the front of the head and folded under the body. Forewings hardened at the base and membranous at the tip (hemelytra), overlapping on the back; a triangular scutellum between them. Nymphs look like wingless adults.
How to recognise it : Elongated, leathery, veined forewings (tegmina) folded over the abdomen; hind legs with swollen femurs for jumping; chewing mouthparts. Nymphs bear wing buds.
No opportunist on this site is linked to this group yet.
How to recognise it : Four membranous wings covered in scales that rub off on the fingers; mouthparts form a proboscis coiled under the head; thread-like, feathery or clubbed antennae. The adult does no direct damage: its caterpillars do.
Annona fruit borer Box tree moth Cactus moth Citrus leafminer Cocoa pod borer Codling moth Coffee leaf miner Cotton bollworm (Helicoverpa) Eggplant fruit and shoot borer European corn borer European grapevine moth Fall armyworm False codling moth Greater wax moth Large white butterfly Leek moth Litchi fruit borer Macadamia nut borer Oak processionary moth Olive moth Oriental fruit moth Palm borer moth Pine processionary Pink bollworm Potato tuber moth Quinoa moth Sugarcane borer Tomato leafminer
How to recognise it : Elongated body; four strap-like, almost veinless wings fringed with setae; asymmetrical rasping-sucking mouthparts; legs ending in a bladder. They rasp tissues, which turn silvery and speckled.
How to recognise it : Four transparent membranous wings, the hind ones hooked to the forewings by a row of hooks; chewing mouthparts; in most, a constricted “waist” (petiole) between thorax and abdomen. Worker ants are wingless, with a one- or two-knotted petiole and elbowed antennae.
How to recognise it : Piercing beak arising from the back of the head; wings held roof-like over the body; jumping hind legs. Leafhoppers and planthoppers: bristle-like antennae. Psyllids: 10-segmented antennae and branched wing veins.
How to recognise it : Soft, pear-shaped body, piercing beak, thread-like antennae; almost always two tubes (cornicles) at the rear of the abdomen and a tail (cauda). Winged and wingless forms in the same colony; wings, when present, are held roof-like. Phylloxera has no cornicles and forms galls.
How to recognise it : Piercing beak; four wings covered in waxy powder, held almost flat or low and roof-like over the body; they fly up in a cloud when the plant is shaken. The larvae, with no visible legs, are flat scales fixed to the underside of leaves.
How to recognise it : A single pair of membranous wings with two club-shaped halteres behind them; 3-segmented antennae, the last segment bearing a bristle (arista). Larvae: maggots with no head or legs.
Carrot fly Cattle warble fly (Hypoderma) Common green bottle fly (sheep strike) Horn fly Housefly Mediterranean fruit fly Melon fly Narcissus bulb fly Olive fruit fly Onion fly Sheep bot fly Sheep ked Spotted wing drosophila Stable fly Walnut husk fly
How to recognise it : A single pair of wings and two halteres; thread-like or feathery antennae with many segments. Many bite animals (biting midges); others form galls on plants (gall midges).
How to recognise it : Wingless females fixed on the plant, legs absent or hidden, under a hard shield or covered with cottony or powdery wax: they look like scales or lumps rather than insects. Only young crawlers move. Males, when present, have a single pair of wings and no halteres.
Black scale California red scale Pineapple mealybug Pink hibiscus mealybug Prickly pear cochineal San José scale Vine mealybug
How to recognise it : Wingless, body flattened top to bottom, legs ending in claws for gripping hair or feathers; eyes reduced or absent. They spend their whole life on the animal. Includes the wingless sheep ked, recognisable by its head sunk into the thorax.
How to recognise it : Floury powder on the surface of leaves, shoots or fruit that rubs off with a finger; underneath, the tissue yellows or dries. Appears even in dry weather.
How to recognise it : Oily or translucent-looking spots on the upper leaf surface and, underneath, a fine down in damp weather; lesions spread fast with no sharp edge.
Basil downy mildew Chamomile downy mildew Cucurbit downy mildew Downy mildew Late blight Lettuce downy mildew Onion downy mildew Quinoa downy mildew Sunflower downy mildew
How to recognise it : Raised, powdery pustules that stain the finger when rubbed, mostly on the underside of leaves; sometimes on stems and fruit.
Asian soybean rust Coffee leaf rust Leek and garlic rust Mint rust Rust Tarragon rust
How to recognise it : Sharp-edged spots that stop growing, often with concentric rings or dots (fruiting bodies) visible with a hand lens in the centre; on fruit, scabs or sunken spots.
Alternaria (early blight) Alternaria leaf blight of carrot Anthracnose Ascochyta blight of chickpea Black Sigatoka 
Black rot of grapevine Brown spot of pear (Stemphylium) Cercospora leaf spot of beet Chocolate spot of faba bean Early leaf spot of peanut Helminthosporium leaf spot Olive leaf spot Rice blast Rose black spot Scab Septoria leaf spot of celery Septoria tritici blotch Tulip fire
How to recognise it : Angular spots bounded by veins, water-soaked or greasy-looking, sometimes with a halo; no powder or mould. Sometimes sticky ooze droplets, shoots that wither into a crook or oozing cankers. Test: a cut stem placed in a glass of water releases milky threads.
Bacterial canker of kiwifruit (Psa) 
Bacterial diseases Fire blight Walnut blight
How to recognise it : Fruit, flowers, stems or tubers that rot and become covered with felt, rings of cushions or hard bodies (sclerotia); fruit may stay mummified on the plant.
Black rot of grapevine Botrytis (grey mould) Brown rot (Monilinia) Frosty pod rot Green and blue moulds of citrus Phytophthora palmivora (black pod) Sclerotinia rot
How to recognise it : Area of dead bark, sunken or cracked, sometimes surrounded by callus ridges, with dots (fruiting bodies) or oozing liquid; the branch beyond it dries out.
Bacterial canker of kiwifruit (Psa) Chestnut blight Cypress canker Esca of grapevine Fruit tree canker (Nectria) Sudden oak death
How to recognise it : The plant, or part of it, wilts although the soil is moist, often on one side only; cutting the stem at the base shows darkened vessels compared with a healthy plant. If the cut releases milky threads in a glass of water, the cause is a bacterium.
Bayoud disease of date palm Fusarium wilt Panama disease tropical race 4 (TR4) Verticillium wilt Xylella fastidiosa
How to recognise it : Mosaic (mix of light and dark areas), rings, puckered, curled or distorted leaves, stunted plant; mottled or rough fruit. No powder, mould or sharp-edged spots. Many viruses are spread by aphids, whiteflies or thrips, or by tools and hands.
Banana bunchy top virus Citrus tristeza virus Cucumber mosaic virus Papaya ringspot virus Sharka (plum pox) Tobacco mosaic virus Tomato brown rugose fruit virus Tomato spotted wilt virus Tomato yellow leaf curl virus
How to recognise it : Witches' brooms (many thin shoots at one point), small and numerous leaves, flowers turning leafy, sector-wise and asymmetric yellowing or reddening, shoots that fail to ripen. Spread by leafhoppers or psyllids.
Aster yellows Huanglongbing (citrus greening) Stolbur (bois noir)
How to recognise it : Blistered, thickened, brittle and distorted leaves from bud burst, later covered with a thin bloom; they drop early. No insects inside the distortions.
How to recognise it : Club-shaped roots (brassicas) or bead-like swellings on fine roots, sometimes attached cysts; the plant wilts in the heat of the day and grows poorly. Legume nodules, by contrast, come off easily and sit on the side of the root.
How to recognise it : Soft, darkened roots or collar whose bark slips off when pulled; sometimes felt and hard bodies at the stem base. Plants decline in patches, especially in waterlogged soil.
How to recognise it : Grains filled with a strong-smelling powder instead of flour, or spikelets that dry out early with mould at their base; shrivelled grains.
How to recognise it : Diarrhoea, weight loss, dull coat or wool, cough or oedema, lower production; in bees, droppings at the entrance and weakening colonies. Only a faecal test or a vet can confirm the cause.
Barber's pole worm Cattle lungworm Coccidia (Eimeria) Common liver fluke Nosema (Nosema ceranae) Poultry roundworm
How to recognise it : Patchy brood, sunken, darkened or perforated cappings, dead larvae that stretch into a thread when pulled out with a matchstick, silk tunnels in combs, larvae in the honey, mites on the bees. If foulbrood is suspected, notify the veterinary services.
American foulbrood (Paenibacillus larvae) Greater wax moth Small hive beetle Varroa mite
This simplified key is written in our own words from the morphological features described in the following works and tools. For a reliable identification down to species, use these specialised keys or consult a diagnostic laboratory.
Slugs and snails
Chilli thrips
Ants
Brown planthopper
Aphid
Whitefly
Leveillula powdery mildew
Peach leaf curl
Common bunt of wheat