Paralecanium expansum metallicum (scale insect)
Adult females of the scale insect species Paralecanium expansum metallicum are a striking silver-metallic colour when alive.
Scale insects are true bugs, members of the order Hemiptera that feed on liquid food via modified tubular mouthparts known as stylets.
While all scale insects feed on plants, some attack crop plants and are notorious agricultural pests.
Scale insects are very diverse in appearance but all females have reduced mobility as adults. Some can only move about at all in the first nymphal stage, termed a crawler.
Species detail
Photomicrograph of the curious modified marginal setae of Paralecanium expansum metallicum.
Paralecanium expansum metallicum belongs to the family Coccidae. These are known as soft scales because they are not protected by a cover (known as a test).
This particular scale insect has a strange and attractive appearance. They look like tiny metallic discs on leaves. Under a microscope the adult female is also a most curious-looking insect, with extraordinary marginal setae shaped like tiny table tennis bats.
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Distribution and habitat
Paralecanium expansum metallicum appears like a splash of metal solder on the leaf. Learn where in the world this species is found, the type of habitat it lives in and threats to its survival.
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Biology
Find out about the life cycle of this species and the interesting differences between male and female scale insects, and watch a film of crawlers emerging from the adult female.
Images
A living adult female Paralecanium expansum metallicum scale insect.
Paralecanium expansum metallicum adult female. The light has been adjusted to display the dorsal secretions in polygonal blocks. It also shows the roughened surface which seems to contribute to the insect's iridescence.
Phase-contrast photomicrograph of a Paralecanium expansum metallicum crawler, 0.5mm long. The specimen has been stained pink to make it easier to locate on the slide.
Photomicrograph of the curious modified marginal setae of an adult female Paralecanium expansum metallicum, which are shaped like tiny table tennis bats.
About the author
Dr Jon Martin
Former Curator of Hemiptera, Department of Entomology.
Author comment
I have chosen this scale insect because it is in its own way spectacular, with an extraordinary and attractive appearance.
Glossary
Marginal setae
Hair-like structures at the edge of the insect.
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Reference
Green, E E (1904) On some Javanese Coccidae: with descriptions of new species. Entomologist's Monthly Magazine 40: 204-210.
This paper describes 4 new species and 3 new varieties, with collection notes on 20 other scale insects.