Under the Gums: The Sticky Truth About Lerp, Sap & Bird Acid
Berwick's leafy avenues. The grand old gums on the acreage around Narre Warren North. The established canopy shading the premium streets of Botanic Ridge. It's beautiful — and it's brutal on a dark car parked underneath. The threat isn't one thing; it's three, working together: sticky honeydew, tree sap, and acidic bird droppings. Here's what's really landing on your paint, and how to deal with it without making things worse.
That sticky film usually isn't sap
This surprises people. The fine, sticky mist that coats a car parked under a gum is mostly honeydew — and honeydew is insect waste, not tree sap. Our eucalypts host a tiny sap-sucking insect called the red gum lerp psyllid. Its young build little white caps on the leaves (the "lerps") and excrete copious amounts of sugary honeydew that rains down onto everything below: leaves, footpaths, outdoor furniture… and your bonnet.
On its own it's just sticky and sugary. The problem is what follows: honeydew feeds a black, grimy sooty mould that grows on any surface it coats, leaving that dull, dirty film you can't quite wash off. Add in real sap and resin from damaged limbs, gum-flower drop, and the acidic bird droppings that always come with a busy tree, and a dark car under the gums is fighting on three fronts at once.
Why it marks your paint
Left on a warm panel, honeydew and sap bake on and harden, the sooty mould sets into a film, and the whole sticky mess grabs every bit of dust that floats past. Bird droppings are the urgent one: they're acidic (around pH 3–4.5) and on a hot day they can begin etching the clear coat within minutes to a few hours. On dark paint especially, every one of these leaves a mark you'll see in the sun.
The one rule that saves your paint
Same as every sticky, gritty threat: never wipe it off dry. Dragging hardened honeydew, sap or a dried dropping across the paint is sanding it — instant swirls and scratches. Soak and lift, every time.
Try it yourself
Catch it early and gently, and most of this is a genuine DIY job.
Honeydew & sap: soak the spot with warm soapy water or a quick-detailer spray and let it dwell for a minute or two to soften. Then lift it with a soft, plush microfibre — one gentle wipe, fold to a clean side, repeat. Patience beats pressure: soften it again rather than scrubbing.
Bird droppings — move fast: soak a microfibre in water or quick-detailer, lay it over the dropping for 30–60 seconds to soften, then wipe once and fold away. Speed genuinely matters here, because the acid is etching while it sits.
Park smart: in peak honeydew season, avoid parking directly under the worst trees if you can, or throw a cover on. Free, and it prevents the problem entirely.
A kit that handles it: a good quick-detailer spray, a generous stack of plush microfibre towels, and a pH-neutral shampoo for the regular wash.
Where it pays to call the Don
When it's baked on or it's already left a mark, gentle home methods hit their limit.
Bonded honeydew, sap or sooty-mould film needs proper decontamination and the right solvents used the right way. Eucalyptus oil, for instance, is a genuine solvent for this stuff — but used carelessly it can affect trim and finishes, so it's a job for someone who knows the dose.
If it's already etched — rings, dull spots, marks that won't wash out — that's machine paint correction, and that's the work it's genuinely worth not learning on your own car.
A ceramic coating is the real answer under the gums. It makes the surface so slick that honeydew, sap and droppings struggle to bond — they sit on top and rinse off, and you get far more time before any acid can bite. It slows the damage right down; it doesn't make the car immune, and nothing honestly can.
The honest bottom line
The gums aren't going anywhere, and you wouldn't want them to — they're half the reason these suburbs are so lovely to live in. You just need the right habit: soak and lift, never wipe dry, and get bird droppings off fast. Do that and you'll keep a dark car looking sharp yourself. When the sticky stuff has bonded or left a mark — or you want the paint sealed so it stops grabbing on in the first place — that's where we come in. Every detail matters, and under the gums, the small, quick ones matter most.
Related reading: the deeper dive on the acidic side of this is in Bird Droppings and Tree Sap: why a few hours can cost you a respray.
In your area: we bring mobile detailing, paint correction and ceramic coating to your driveway under the canopy — see Berwick, Narre Warren North and Botanic Ridge.
Sources & further reading
- Business Queensland — Psyllids and lerps (what lerp and honeydew actually are).
- UC IPM — Sooty mould and honeydew on cars and surfaces.