The red bay psylid (Trioza magnolia) is responsible for galls on the edges of the leaves of red bay (Persea borbonia) and swamp bay (Persea palustris). The galls are so ubiquitous and distinctive that they are sometimes used as a key to identification.
The red bay psylid is thought to lay its eggs under the epidermis of the leaves. Upon hatching, nymphs feed upon the edges of the leaves, and, ultimately, the nymph is enveloped — and somewhat protected — by the pocket-like gall.
Click here to read/see more about the red bay psylid from Featured Creatures website of the University of Florida Department of Entomology and Nematology.
Ultimately, the adult psylid emerges from the gall, and the gall darkens. Insectivorous birds reportedly sometimes peck open the green galls for a “snack”.
Red bay psylids have only been found “bay” trees. Some taxonomists “lump” and do not differentiate between red bay (Persea borbonia) and swamp bay (Persea palustris). Swamp bay is found in wetter locales and is said to be marked by a rusty pubescence on the mid vein of underside of its leaves.
This intimate relationship of gall maker and bay tree — present for eons — has been dramatically disrupted by the introduction of laurel wilt (Raffaelea lauricola), an exotic disease, spread by the redbay ambrosia beetle (Xyleborus glabratus). These invasive interlopers threaten the long-lived interaction between bay trees and the red bay psylid.
Though once a not uncommon plant of hammocks, especially coastal hammocks, in Florida, very few large bay trees remain. You still can find some small bay trees at the Oslo Riverfront Conservation Area and can delight in seeing graceful galls curling up the edges of their leaves.