Leatherjackets are what we call the soil dwelling grubs of long, dangly-legged flies known as Crane flies or Daddy-Longlegs.
The grubs are tubular, greyish-brown in colour and have no legs or visible heads.
They develop from eggs that the adult Crane flies usually lay into lawns at the end of summer, and throughout Autumn, the young leather jackets feed on grass roots before hibernating underground over winter.
Come Spring, the leather jackets resume feeding, often causing unsightly patches of dead and dying grass across the lawn before they pupate in mid-summer. After a couple of weeks the next generation of adult Crane flies emerge to mate and then re-infest their eggs back into the lawn.
An interesting fact, which is useful to know when Leatherjackets are causing a problem within a lawn is that when the weather is dry, the grubs move to a greater depth in the soil, but when the weather is wet they move to just below the surface of the lawn. Birds, such as starlings and crows, love to eat leatherjackets, so by keeping a lawn regularly watered during the summer months the grubs will always be near to the surface and within easy reach for the birds.