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July 26, 2026Sources cited
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Science & Nature • Entomology

Aphid

Aphids are a large group of small, soft-bodied, sap-sucking insects in the superfamily Aphidoidea, commonly called plant lice.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 26, 2026|2 min read| Fact-checked

Aphids are a large group of small, soft-bodied, sap-sucking insects in the superfamily Aphidoidea, commonly called plant lice. They are widespread on plants worldwide and are well known as agricultural and garden pests because they can weaken plants and transmit plant viruses.

Description

Aphids are tiny, soft-bodied insects with sucking mouthparts and a pear-shaped body. They range in size from about 1 to 8 mm long. Many species have visible cornicles, a pair of tubelike projections on the abdomen. Common colour forms include green, black, yellow, pink, brown, and white. Aphids often live in clusters on actively growing plant tissue such as leaves, stems, flowers, and sometimes roots.

Biology and life cycle

Aphid life cycles can be complex and may include both asexual and sexual reproduction. Some species alternate between different host plants during their life cycle.

Ecological and economic importance

Aphids are important plant pests because they remove sap, excrete honeydew that can lead to sooty mold, and spread plant diseases. Their feeding can reduce plant vigour and crop yields. They can stunt growth, distort leaves, and transmit plant viruses.

Distribution and diversity

Aphids occur worldwide and are especially diverse in temperate regions. More than 4,000 species have been described worldwide. In Canada, aphids are common pests in gardens, greenhouses, nurseries, and crops, and Canadian extension resources describe them as frequent insects on many plants.

Key facts

  • Aphids are small insects that feed by sucking sap from plants.
  • They can stunt growth, distort leaves, and transmit plant viruses.
  • Many species have cornicles, a pair of tubes near the rear of the abdomen.
  • More than 4,000 aphid species are known worldwide.
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Canadian context

Aphids are common pests in Canadian gardens, greenhouses, nurseries, and crops, and Canadian extension resources describe them as frequent insects on many plants.[16][17]

Frequently asked questions

What are aphids?
Aphids are small, soft-bodied, sap-sucking insects in the superfamily Aphidoidea, commonly known as plant lice.
Why are aphids considered pests?
They can weaken plants by removing sap, distort growth, spread viruses, and leave honeydew that supports sooty mold.
What do aphids look like?
They are usually tiny, pear-shaped insects with long antennae, sucking mouthparts, and often two cornicles on the abdomen.
Where are aphids found?
They are found on many kinds of plants worldwide, especially on leaves, stems, flowers, and sometimes roots.
How many aphid species are there?
The provided sources report more than 4,000 aphid species worldwide.
Do all aphids damage plants?
Most are plant feeders and many are pests, but the severity of damage varies by species, host plant, and infestation level.

References

  1. Encyclopaedia Britannicahttps://www.britannica.com/animal/aphid
    Supports: General definition, morphology, cornicles, and pest effects.
  2. Royal Horticultural Societyhttps://www.rhs.org.uk/biodiversity/aphids
    Supports: Common names, taxonomy, size range, colour variation, and feeding habits.
  3. University of Minnesota Extensionhttps://www.extension.umn.edu/yard-and-garden-insects/aphids
    Supports: Identification, symptoms, and management context; size, colours, and cornicles.
  4. University of New Hampshire Extensionhttps://extension.unh.edu/resource/aphids-fact-sheet
    Supports: Sap feeding, virus transmission, honeydew, and sooty mold impacts.
  5. University of Florida IFAShttps://mrec.ifas.ufl.edu/lsolab/aphids/
    Supports: Global species count and pest importance.
  6. ScienceDirect Topicshttps://www.sciencedirect.com/topics/agricultural-and-biological-sciences/aphidiidae
    Supports: Species count, life-cycle complexity, reproduction, host alternation, and distribution context.