Question: Crane flies for ten years

By | 10/09/2020
A crane fly

I received this interesting question in August 2020 about crane flies attacking a lawn year after year. Gemma writes:

Hi Kris,

We’ve had leatherjackets now for ten plus years, gradually getting worse every year. We were of the understanding that crane flies return to where they were larvae.

Neither of our neighbours appear to have the issue on the same scale we have. We are thinking about just putting a black sheet down when we start seeing the crane flies to stop them laying eggs. It seems obvious but no one seems to suggest this.

Nematodes haven’t worked two years running now and we scarify and aerate every year.

Gemma, Via Ask a Question

Hi Gemma,

Thanks for your question. A couple of interesting things going on here.

Leatherjacket is the common name for the larvae of crane flies (Tipulidae).

I would expect something else to be going on with your lawn to be honest. It is very unusual to have leatherjackets for ten years running. There may be something else causing the repeated thinning of the lawn. This may be wet soil, heavy shade, compaction or any number of other problems.

Do leatherjackets return home?

Leatherjacket numbers do tend to rise and fall over the years. Sometimes there are hardly any, sometimes there are plague-like numbers. I would look at improving your lawn in other areas. A good lawn is rarely affected by a minor leatherjacket infestation.

The fact that you said that you scarify every year may be a clue. This may not be doing your lawn much good. Why are you scarifying? Scarification is for pulling out the thatch layer and cleaning the lawn. Scarifying without a reason can damage a lawn. It can knock the grass back to such an extent it can look like leatherjacket damage. Unless you have particularly thatchy, fescue grass or are grossly overfeeding, scarifying every two years is plenty. Keep up annual aeration though. That is helping.

Repairing your lawn quickly after the leatherjackets have been dealt with is important. Getting the grass back to strength quickly will reduce the amount of damage in future.

You do suggest covering the lawn to prevent the crane flies laying eggs. Of course, any barrier method would work. If your lawn is small and you don’t mind it being completely unusable lawn for several weeks at the end of the summer. Using black plastic would be a bad idea though. This would block out the light and eventually kill the grass. I would suggest transparent material such as enviromesh. This would still let through air, light and water down to the grass, and still be a barrier to crane flies.

Barrier methods to block out crane flies?

Barrier methods are not usually suggested for lawns as the areas are often too big for it to be practical.

Nematodes do seem to only bring sporadic success to leatherjacket control. I would not rely on them as your only control method.

Going forward though, I recommend contacting a local, independent lawn care expert. They will take a professional look at your lawn and suggest improvements. A quality feeding regime will always help your lawn to be more resistant to insect damage. Changing your species of grass may be an option. Some dwarf-rye grasses and tall fescues don’t produce much thatch. They do seem to be less prone to egg-laying from the insects.

Also, have a look at the layout of your garden. Crane flies don’t return to where they were born. They go where the wind takes them. If they can’t get out of your garden, they will stay. If you have a wind-trap or solid fencing, then the flies may be getting trapped.

Improve the airflow in your garden. Plant hedging and other plants rather than fences. Put trellis and climbers up hard surfaces to break up wind currents. Not only would this give someway for the flies to escape, birds would appreciate it. They are voracious predators of the flies in summer and would help to keep numbers down for you.

If you do find that your lawn is a haven for leatherjackets every year, have a read of my Leatherjacket Lawn Pests – The Complete Guide. Following these steps will help keep numbers down and improve your grass year on year.

I hope this is useful. Thanks for reading!

Kris Lord
The Lawn Man

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