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How to identify it
- In summer, look for dense aphid colonies on floating lily pads and other pond plants; the aphids walk on the water's surface and crawl down emergent stems to feed underwater.[1]
- Hairs on the body trap air, which lets the aphids stay underwater for a time.[1]
- On fruit trees in spring the same species is known as the reddish-brown plum aphid.[1]
Where it lives
Nearly cosmopolitan, found in all but the coldest land habitats. In the United States, Texas A&M AgriLife Extension has written about it as a pest of water lilies in ponds.[2][1]
Biology and life cycle
It alternates hosts. In late fall, winged adults leave the pond for fruit trees in the genus Prunus, such as peach, apricot and almond, and females lay eggs in cracks in the bark. The eggs are the only stage that survives the winter.[1]
In spring, several generations feed on the trees. In mid- to late summer the aphids move back to the water, onto waterlilies, cattails, buttercup and knotweed.[1]
It prefers rosaceous plants and plants that grow in or near water, and has been recorded on plants in at least 45 families.[2]
Reproduction can be rapid enough to blanket plants.[1]
Damage and signs
- Heavy feeding in late summer and early fall can brown and dry out the leaves of water plants, though the damage often comes as the plants are starting to die back for winter anyway.[1]
- It can be extremely destructive in aquatic gardens and nurseries, and it is a pest of rosaceous plants in spring.[1][2]
- It has been implicated in spreading several plant viruses.[1][2]
Health risk
The sources describe it only as a plant pest; neither mentions any risk to people or pets.[1][2]
Control
Traps and physical control
Swish infested leaves in the pond water or wash the aphids off with a stiff stream of water. This likely works best in ponds with fish or other aquatic predators that eat the floating aphids.[1]
Pesticides
Don't use malathion or other common aphid sprays on pond plants: few insecticides are labeled for aquatic plants because most are highly toxic to fish and aquatic invertebrates. Soaps or oils can be used by lifting plants out of the water, spraying and rinsing them, and returning them quickly.[1]
Common questions
- What are the tiny bugs covering my water lily pads?
- Likely waterlily aphids, which build up on waterlilies and other pond plants in late summer and early fall.[1]
- Can I spray the aphids on my pond plants?
- Not with ordinary aphid insecticides, which are mostly highly toxic to fish and aquatic invertebrates. Swishing the leaves in the water or hosing the aphids off is the usual fix.[1]
- Where do waterlily aphids go in winter?
- Winged adults fly to Prunus trees such as peach, apricot and almond in late fall and lay eggs in bark cracks; the eggs survive the winter.[1]
Sources
- Texas A&M AgriLife Extension Service, “Aquatic aphids, Insects in the City (August 22, 2011).” citybugs.tamu.edu/2011/08/22/aquatic-aphids/ (accessed 2026-11-09)
- USDA APHIS PPQ Identification Technology Program (idtools.org), “Rhopalosiphum nymphaeae fact sheet, AphID: Identification guide for cosmopolitan and polyphagous aphid species (C. Favret and G. Miller).” www.aphid.aphidnet.org/Rhopalosiphum_nymphaeae.php (accessed 2026-11-09)
- iNaturalist, “Rhopalosiphum nymphaeae taxon page (order and family).” www.inaturalist.org/taxa/142766 (accessed 2026-11-09)