Live and Let Live?

Monday July 16, 2012


Mr Pest Control


I have a customer who has a serious cicada killer problem. He has a very thick lawn that he waters to prevent them on his property. The neighbor to his left does not water his lawn and has a much larger number of the wasps and the property to the right has no vegetation and has many wasps as well digging into the sides of the hill. It also has a large drainage pit for the development. I'm out of ideas as to how to help him. I think he is doing everything he can but is there anything else I can tell him to help the situation? Do Purple Martins eat cicada's? Are their any other natural predators that would be of help to him? If you have any advice that would be greatly appreciated.


Mr Pest Control


The huge Cicada Killer wasps are common in the eastern U.S. but do not live in the western states, so I personally have never had experience with them. We do have many other kinds of solitary, predatory wasps that capture other insects, create burrows and chambers in the soil, and provide that captured insect as food for their developing larvae, but none nearly the size of the cicada killers. A couple of things really are important here. The first is the extraordinary benefit that all of these solitary predator wasps provide to us with their feeding on cicadas, caterpillars, crickets, and other insects that truly are the pest problems in the garden. The second is the fact that these wasps do not have social structures and therefore do not have the instinct to rush at someone to sting them when they approach a colony of the wasps. There are no colonies of cicada killers, only large numbers of them working independently. 

Now, a female cicada killer is quite capable of inflicting a painful sting, but this would happen only if that  wasp was directly threatened, such as captured in a hand or confined within clothing, and every reputable resource on these wasps states that stings from them are quite rare. It appears that the benefit far outweighs the threat, and the ideal thing would be for these customers to begin to appreciate the work the wasps do, including that free aeration of the turf, and at some level start to enjoy having them around. All that being said I also recognize that the digging of the females can make a pretty large mess of a nice lawn, and when hundreds of them are working on a single turf area it may become intolerable. 

The female wasp looks for soil that is the right consistency to allow her to dig that tunnel and create the side chambers for her offspring to develop in. Sand would collapse too quickly, but other soils may hold up just right. Watering a lawn heavily is probably not enough water to discourage them, and anecdotes about using water to keep the wasps away tell us that it is done by actually flooding each individual burrow so completely that the female wasps finally decide to go somewhere else. This means going to each burrow opening daily and using the garden hose to fill that burrow with water until the wasps no longer are using that area. 

Every other treatment for these wasps also seems to be hole-by-hole, and area wide applications of insecticides do not seem to be particularly effective. Some level of kill of the adult wasps may be possible by spraying a contact insecticide over the turf, but this will kill only a few and others will continue to work and the area will continue to attract them. This is going to be a very seasonal phenomenon, as the adults are only working in July and August, but that still is a long time. Insecticide applications are effective only when applied directly into the burrow opening, and this does appear to be successful, if only for this one season. Various pyrethroids in either dust or liquid spray form can be poured or dusted in and this will kill the working female wasp. Even "home" remedies by people who think they are using non-pesticides rely on treating each hole individually. 

Covering bare soils with gravel or garden mesh will discourage the wasps from digging. There even are many university websites that suggest that a tennis racket will quickly "dispatch" the wasp, but now you could be aggravating that wasp enough to elicit a sting if you miss with the first swing. Tolerance and appreciation are always preached by wasp experts. From what I can read Purple Martins may very well eat cicada killers, as they feed on nearly any kind of insect available, but predators like birds do sometimes figure out that large wasps can sting them and may avoid the risk. It is rare for any predatory bird or mammal to actually eliminate an insect problem from an area, so if they do eat these wasps they are not going to eat them all. 

Mr. Pest Control

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Please note, Mr. Pest Control is answering questions supplied by PMP customers across North America. His answers are generated from industry and manufacturer-provided information. The answer may not be specific to the laws and regulations for your State, Province, Territory or Country. In addition, products mentioned may not be registered and or available in all areas. Always check with your local Univar office for specific information to your area. Always read and follow label directions.