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Superfamily Coccoidea - Scales and Mealybugs

Armored Scale? - Ceroplastes Horned Scale and Crawlers on California Buckeye leaf. - female Coccoidea elongate hemlock scale - Fiorinia externa - male - female false pit scales - Lecanodiaspis prosopidis - female Ceroplastes? - Ceroplastes Coccidae, lateral - male Fiorinia externa
Kingdom Animalia (Animals)
Phylum Arthropoda (Arthropods)
Subphylum Hexapoda (Hexapods)
Class Insecta (Insects)
Order Hemiptera (True Bugs, Cicadas, Hoppers, Aphids and Allies)
Suborder Sternorrhyncha (Plant-parasitic Hemipterans)
Superfamily Coccoidea (Scales and Mealybugs)
Synonyms and other taxonomic changes
for recent summary of classification and higher taxa relationships see(1)
~1100 spp. in ~250 genera of 28 families in our area; estimated almost 8,000 spp. in 1,137 genera of 45 families worldwide(2)
keys to quarantine spp. in(3)
Parasitic on plants, they drink plant fluids through their piercing, tube-like mouthparts. Like many parasites, they tend to specialize in specific groups of plants: knowing what plants they feed on can help greatly in identification.
Life Cycle
While there's some variation, they start as free-moving crawlers, with the females becoming less mobile as they mature. In most groups, the females attach to a single spot and lose legs, antennae, etc., so that they begin to look more like some kind of growth than an insect. Both mobile and non-mobile types develop thick protective layers of wax or other inert substances, often in elaborate shapes- so it's hard to see the actual insect underneath.

The adult males are rarely seen (or at least rarely noticed), but look somewhat like winged aphids:

The female lays her eggs where she is (often in a large sac hidden under her own protective covering), and the crawlers hatch to move on to new feeding sites.
Most gain the protection of ants by secreting a sugary substance called honeydew.
Normally only a minor pest (mostly because they spread diseases), but non-native species that lack natural enemies can build up to devastating numbers. Some of the earliest and most dramatically successful uses of biological control have been against this group.
See Also
Whiteflies undergo a similar legless, attached stage as nymphs, but then both males and females develop into winged adults.
Print References
Howell, J. O. and M. L. Williams. (1976). An Annotated Key to the Families of Scale Insects (Homoptera: Coccoidea) of America, North of Mexico, Based on Characteristics of the Adult Female. Annals of the Entomological Society of America, Vol. 69, No. 2: 181-189. (Oxford Academic)
Works Cited
1.Phylogeny and higher classification of the scale insects (Hemiptera: Sternorrhyncha: Coccoidea)
Gullan P.J., Cook L.G. 2007. Zootaxa 1668: 413–425.
3.Scale Insects: Identification tool for species of quarantine significance
4.The Scale Insects of California. Parts 1-3.
Raymond J. Gill. 1988. Sacramento, Calif. : Analysis and Identification Branch, Division of Plant Industry, California Dept. of Food and Agriculture.
5.The Soft Scale Insects of Florida (Homoptera: Coccoidea: Coccidae)
Avas B. Hamon and Michael L. Williams. 1984. Florid Department of Agriculture & Consumer Services, Division of Plant Industry.