Gardening Harmful insects

Crane Fly: Giant Mosquito or Plant Pest?

Crane fly, European crane fly, Tipula paludosa, mosquito hawk, skeeter-eater, flying daddy longlegs or something like “yuck, that’s really ugly.”

Yes, the big fly with a mosquitolike physique certainly has a lot of names. And can maybe give you a bit of a fright when you first see one.

But let me reassure you right off the bat: this insect doesn’t bite. If fact, the winged adult crane fly doesn’t even feed! However, many people take the poor crane fly for a gigantic mosquito and fear it could drain us of our blood!

True enough, I have to confess that, before I studied biology, this critter used to startle me too!

Lawn damage by an overpopulation of crane fly larvae. Photo: Alec Kowalewski, © Oregon State

I could end this blog right here, having solved the problem of the shock it might cause you when you first see this big fly as it emerges in late summer. But the truth is that this insect, while harmless to humans, does hide a darker side. You see, it’s sometimes responsible for causing lawns to turn yellow, or even of damaging farmers’ fields.

Stem cut by leatherjacket and leatherjacket partially visible.
Young sprout damaged by a leatherjacket. You can barely make it out at the base of the stub, to the lower left. Photo: Jonathan Roy (MAPAQ)

When Two Life Cycles Interact … Badly!

It’s the wormlike larva, which we call a leatherjacket for its leathery texture, that does all the eating.

Several leatherjackets on top of soil.
The larvae of Tipula paludosa, called leatherjackets, live in the first 2 inches (5 cm) of soil and measure from 1/8 to 1 ¼ inches (3 to 40 mm) in length. Photo: Jonathan Roy (MAPAQ)

It feeds mostly on grasses: roots, ground level stems and young leaves. Well-hidden underground, it’s active from the time it hatches at the end of September. When cold weather arrives, it moves deeper underground to spend the winter. Then it moves up again begin to devour your beautiful green lawn as soon as it reawakens in the spring, when soil temperatures reach 41°F (5°C).

Presented in that way, a leatherjacket could still appear quite disturbing! However, only major invasions cause any notable damage. If there are only a few leatherjackets, the usual case, you won’t even notice their presence.

Photo: Élisabeth Taschereau

Look at the cute little face of a baby crane fly. How can you resist sharing a few of your lawn’s roots with it? Although, to be honest, this is really the butt end of the leatherjacket, not its face!

Keeping Crane Flies Away

Although the damage may usually be minor, there are still a few natural ways of avoiding them entirely and preventing adult crane flies from laying eggs in your yard.

First of all, the crane fly likes damp places. If you water your lawn often, that’s like inviting it to settle in, as are poorly drained soils and puddles that hold rainwater. So, try to fix your moisture problems before spending a fortune on insecticides that will likely only give so-so results. Solving your drainage difficulties will be more permanent, less expensive and, in the long run, better for your lawn in every way .

The problem is more difficult to control in farmers’ fields, though. Indeed, since leatherjackets feed largely on grasses and cereals are grasses, our cereal grains are as vulnerable to them as home lawns. Wheat, barley, corn, rice, etc. are smack dab on their menu.

Fields damaged  b leatherjackets.
Originally from Europe, this insect is now also a major crop pest in the United States and Canada. Here you can see damages to a field of oats (left) and of canola (right). Photo: Jonathan Roy (MAPAQ)

In the Old World, there seems to be a pattern of major crane fly emergences every five to seven years. This has not yet been seen in the United States and Canada, where there are no such cycles. Insecticide applications are not very effective against the larvae, and since the adults don’t feed, they are not good candidates for poison treatments either.

Let Mother Nature Do Her Duty

Fortunately, this insect is the prey of several predators. Shrews, frogs, bats and several species of birds will eagerly gobble them up, for example. There are studies following the evolution of this insect in its new territory and there is hope that a natural balance will settle in. After all, the first mentions of Tipula paludosa in Eastern North America date back only 70 years or so. Let’s give Ma Nature time to integrate it into its cycle: she generally handles things so well!

Audrey Martel is a biologist who graduated from the University of Montreal. After more than ten years in the field of scientific animation, notably for Parks Canada and the Granby Zoo, she joined Nature Conservancy of Canada to take up new challenges in scientific writing. She then moved into marketing and joined Leo Studio. Full of life and always up for a giggle, or the discovery of a new edible plant, she never abandoned her love for nature and writes articles for both Nature sauvage and the Laidback Gardener.

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