Horse "Flies" Weren't Bad Enough

Tuesday August 28, 2012


Mr Pest Control


I've been treating a 3-sided shelter that houses horses and the horse owners are complaining about wasps stinging the horses. I've dusted the voids and sprayed around the shelter with Transport Mikron, which seems to help for a few days and then the problem begins again. Any suggestions? Would some type of repellent work better? I know I'm killing the existing wasps, but within a matter of days there are more! I'm sure they are attracted by the manure.

Mr Pest Control


Two things would be important here - determining what kind of wasps these are and then finding their nests. So far it appears you are only attacking the adult wasps, and this is going to be as you have discovered, and be very short lived. You kill some adult wasps that may land on the insecticide you have applied to surfaces, but the source of the problem is going untouched. Generally speaking, wasp control is fairly cut and dry if you are able to find the nest itself. Of course, this depends on whether these wasps are social wasps like yellowjackets or paper wasps or if they are solitary wasps like mud daubers or ground nesting wasps. The solitary wasps would be highly unlikely to sting people or horses, so if these animals truly are being stung then you likely have some colonies of paper wasps or yellowjackets in the area. You really do need to make the careful inspection to find those nests and then treat them directly to kill the queen, the workers in the nest, and then the larvae by removing the nest and disposing of it if possible. 

Even social wasps do not sting unless directly provoked or if someone or something gets too close to their colony, so this could suggest that the nests are very nearby and the horses are simply walking too close to them. In a simple structure like you picture there I am not sure what kinds of voids would exist, but yellowjackets in particular are known to create their nests within structural voids. If this is the case you can treat the opening where the workers are entering and exiting using a contact insecticide, and a dust may be most effective, and hope to kill the workers as they pass over that dust. 

If you are able to find exposed nests, which is more normal for the paper / umbrella wasps, these should be treated directly using a "jet" spray aerosol. The horses should be moved out of the local area while any of this is being done, partly to avoid any exposure to the insecticides but also to avoid additional stings by angry wasps that are agitated by the insecticide. Treating any nests is best done in early evening when it is most likely that the worker wasps will be back on or near the nest. Be sure to wear the proper protective clothing to avoid being stung yourself. 

Mr. Pest Control

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