Series 4 Episode 9: The Insect Invasion: Mud Wasps and the Destruction of Gas Flues

The insect invasion, mud wasps, and the destruction of gas flus.

This is one of those topics that sounds trivial until you understand the consequences.

Mud wasps, also called mud dolba wasps, are native Australian insects that build tube-shaped mud nests in enclosed spaces.

They're harmless to humans, non-aggressive, and in any other context, unremarkable.

But their nesting behaviour in the flues and exhaust vents of gas appliances in motorhomes and caravans creates a genuine safety hazard that puts people at risk every camping season.

The problem is simple.

A mud wasp finds a gas appliance flue, typically the hot water system, the diesel or gas heater exhaust, or the oven and cooktop flue, and builds a nest inside it.

The nest completely or partially blocks the flue.

When the appliance is operated with a blocked flue, combustion gases, including carbon monoxide, that should be exhausting outside the rig instead backdraft into the living space.

Carbon monoxide is colourless, odourless and at sufficient concentration, rapidly incapacitating and fatal.

This is not a theoretical risk.

Incidents involving mud wasp blocked gas flues in Australian caravans and motorhomes have caused serious harm.

It's a well documented problem in the RV community and among gas fitters and caravan service technicians.

Which appliances are at risk? Any gas or diesel appliance with an external flue or exhaust is potentially at risk.

Hot water systems are the most common.

The exhaust flue is typically a small diameter tube terminating on the exterior wall of the rig, exactly the size a mud wasp finds attractive.

Gas heaters with external flues.

Cooktop and oven exhaust vents.

Diesel heaters with combustion exhaust pipes.

Though the exhaust temperature of a running diesel heater typically deters nesting during use, a heater that's been sitting unused for weeks is at risk.

When does it happen? Mud wasps build nests in spring and summer when they're most active.

A rig that sits unused for several weeks during the warmer months, particularly in bush or regional settings, is at meaningful risk of nest building and flues.

Travellers who store their rig between trips and then head out without inspecting flues are the most vulnerable.

How to inspect.

Before operating any gas appliance after the rig has been stored or unused for more than a few weeks, inspect all external flue and exhaust vent openings.