Those spiky little bugs lined up on a twig are treehoppers, and the one Southwest Florida gardeners notice most is the thorn bug. Some, like the oak treehopper, do very little harm. The thorn bug is worth a closer look, mainly when it clusters on young trees or on ornamentals like powderpuff.
Here’s what treehoppers are, which ones you’re likely to see, what UF/IFAS says about the damage, and when treatment makes sense versus leaving them alone.
What treehoppers are
Treehoppers belong to the insect family Membracidae. They feed on plant sap, and their most distinctive feature is an oversized shield over the back of the thorax, called the pronotum, that is often shaped like a thorn, horn, or hood.
Treehoppers excrete honeydew while they feed, as aphids do. That’s what drives most of the complaints about them: sticky leaves, black sooty mold, and ants.
The thorn bug (Umbonia crassicornis)
This is the treehopper UF/IFAS flags as a pest in southern Florida. UF/IFAS Featured Creatures calls it an occasional pest of ornamentals and fruit trees.
What it looks like. Adults are about 1/2 inch long, green or yellow with reddish lines and brownish markings. Females have a tall horn rising from the back of the shield. Nymphs have three horns instead of one.
Where you’ll find it. UF/IFAS lists these hosts among those damaged:
- Hibiscus
- Powderpuff (Calliandra)
- Woman’s tongue tree
- Acacia
- Jacaranda
- Royal poinciana
- Cassias and tamarind
UF/IFAS also reports adult thorn bugs collected on citrus and lychee, but doesn’t list those among the damaged hosts, so an occasional adult there isn’t a sign of an infestation. It lists various other legumes as hosts too, so powderpuff and similar ornamentals are good plants to check first.
What it does. Thorn bugs damage plants by sucking sap and by cutting into twigs to lay eggs. During heavy infestations, nymphs and adults form dense clusters around twigs, branches, and even small trunks. UF/IFAS reports foliage loss and dieback of terminal twigs on some hosts. Young jacaranda and royal poinciana trees with trunks only 1.5 to 2 inches across have been killed by thorn bugs in the Tampa area. Honeydew and sooty mold are a nuisance too, and UF/IFAS notes that heavy honeydew sometimes built up on parked cars.
How long it’s around. Females lay eggs in slits in tender twig bark, and the eggs hatch in about 20 days. There are four generations a year, according to UF/IFAS, and a female guards her colony of 15 to 50 young. Adults and nymphs can be found all year. Heavy infestations have been reported in every season, though probably more often in the cooler months.
Is it new here? UF/IFAS says the thorn bug was first present in Florida in 1843 but stayed rare until the 1940s and 1950s. One report came from Fort Myers, where it apparently arrived on nursery stock, so it has been in Southwest Florida for decades.
The oak treehopper
If the treehoppers you found are on an oak, you’re probably looking at a different species. UF/IFAS describes the oak treehopper (Platycotis vittata) as a large, heavy-bodied, triangular insect, often striped or mottled, living mostly on laurel oak, water oak, and turkey oak, and sometimes on live oak. It occurs wherever suitable oaks grow in Florida (UF/IFAS Featured Creatures).
The damage is minor and mostly limited to small egg-laying scars in twigs. UF/IFAS puts it plainly: “Ordinarily this species does not do enough damage to justify control measures.” If it’s on an oak, enjoy the weird-looking visitors and move on.
Ants, honeydew, and sooty mold
UF/IFAS notes that Florida carpenter ants are fond of the honeydew produced by sucking insects (UF/IFAS), so ants on a branch are a common sign that honeydew-producing insects, including treehoppers, are feeding there.
Sooty mold, on the other hand, does not attack the plant itself. It feeds on honeydew and can block light from the leaves (UF/IFAS Extension Okaloosa County). So a sticky, blackened shrub with treehoppers on it looks worse than it is, unless the insects are also heavily damaging the twigs.
Leave them or treat them?
Use these questions to decide.
Leave them alone if the treehoppers are few, the plant is mature and growing well, or they’re oak treehoppers. Damage on those is usually minor.
Take a closer look if you see:
- Dense clusters on twigs, branches, or a young tree trunk
- Foliage loss or dying twig tips above the cluster
- A young tree, like a jacaranda or royal poinciana, with a trunk only an inch or two thick
- Heavy honeydew building up on cars or outdoor furniture
If it’s the thorn bug, here’s the honest state of things. UF/IFAS says control research on it is limited because outbreaks are sporadic. The UF/IFAS Volusia County Extension office, writing about thorn bugs, says there are neither biological treatments nor specific chemical products recommended for this pest, and mentions horticultural soaps and oils for heavy infestations (UF/IFAS Extension Volusia County). If you use one, choose an EPA-registered product labeled for the plant and the pest, and follow the label.
For a young tree that’s being hit hard, or a tall tree you can’t reach, it’s worth getting a landscape professional or your county UF/IFAS Extension office involved early. Waves Pest Control offers tree and shrub care in Lakewood Ranch and in Bradenton. If ants are swarming the plant, our ant control guide is a good next read, and the guide to scale insects covers another common source of honeydew. For pricing, use our pest control calculator.
Frequently Asked Questions
What are the spiky bugs on my plant?
If they’re green or yellow with a tall horn, clustered on a twig, they’re likely thorn bugs, a treehopper UF/IFAS describes as an occasional pest of ornamentals in southern Florida. Treehoppers on oaks are more likely oak treehoppers.
Are thorn bugs bad for my plants?
They can be. They suck sap and cut twigs to lay eggs, and UF/IFAS reports foliage loss, twig dieback, and young trees killed in heavy infestations. A few on a mature plant is a much smaller concern.
What plants do thorn bugs attack?
UF/IFAS lists hibiscus, powderpuff, acacia, jacaranda, royal poinciana, cassias, tamarind, and other legumes among the damaged hosts. Adults have also been collected on citrus and lychee, but those aren’t listed as damaged.
When are thorn bugs active in Florida?
All year. UF/IFAS says all stages can be found year-round, with heavy infestations reported in every season and probably more in the cooler months.
Why are there ants around the treehoppers?
Ants collect the honeydew that treehoppers and other sucking insects excrete. UF/IFAS notes that Florida carpenter ants are fond of that honeydew, so ants on a branch often point to sap-feeding insects above them.
Should I spray for treehoppers?
Usually not for a few treehoppers, and not for oak treehoppers at all, according to UF/IFAS. For heavy thorn bug infestations on young or high-value trees, ask a professional or your UF/IFAS Extension office first, and follow the product label.
