I am noticing a strange phenomenon on my motorcycle radiator: when parked, nearby yellowjackets flock to it and seem to get quite aggressive. I've actually noticed one of them stinging the radiator!

I've also noticed this happens with parked cars. Wasps fly in and out through the grille and seem strangely attracted to the area surrounding the radiator.

It also happens when the engine is cold, so warmth is probably not the answer. My theory is that the dead insects on the radiator excrete some kind of chemical that angers wasps. Has anyone here noticed this phenomenon as well?

(Note that I live in the Netherlands and by "wasps" mean the smaller kind that is probably referred to as "yellowjackets" in the US)

  • I would spray some hornet spray on the radiator, see if this keeps them away. Strange phenomena for sure. – Moab Aug 17 '20 at 14:22
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    Perhaps it resembles a honeycomb in their view, and/or they detect the sweet smell of glycol. I see this question has been on the usual rounds of facebook, quora etc. My answer is because the car is a Wolseley Hornet. – Weather Vane Aug 17 '20 at 20:04

Yellowjackets are omnivorous, meaning part of their diet consists of other bugs. One thing radiators are full of are dead insects which are easy to forage. This also explains why heat doesn’t play into their activity. Your best defense is a good wash.

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