Leatherjackets, are the larvae of the Cranefly / Daddy Longlegs.
The 25mm (1") adult fly that appear from late August to October do not cause plant damage.
The male and female cranefly can be identified by comparing the tip of their abdomens.
In the male the tip is blunt, whereas in the female, it is pointed.
The female crane fly lays up to 300 black, shiny eggs mainly at night, from mid-July to late September.
Eggs are laid on the soil surface, or at depths of about 10mm, and take about 11-15 days to hatch.
When the grey, legless larvae (leatherjackets) emerge they begin feeding immediately, and continue to do so throughout the autumn and during warm periods in winter.
During the day the larvae remain under the soil, but on wet nights may appear above the surface and feed on plant stems.
They eat the stem at the soil level, and may strip some upper roots, severely affecting growth or even killing the plant/s.
Wilting plants and yellow/brown patches on lawns are often signs that they are active in the area.
Larvae overwinter in the soil until spring, when they begin feeding again.
They stop feeding around mid May, when they pupate.
Larvae can be up to 40mm (1½") in length when they reach their full size.
The pupae that appear in August have rows of spines along their sides which enable them to move up and down within the soil during wet and dry periods.
Flocks of starlings on a lawn often indicates that there are larvae / pupae around.
Insecticide sprays against adults are of no value, due to crane flies not feeding between emergence and the laying of their eggs.
The most successful way to control the larvae is to use the nematode Steinernema feltiae.
Mild winters can cause the numbers of leatherjackets to soar, resulting in huge amounts of damage to lawns during this period.
Heavy infestations can be removed by covering small areas of the lawn with black polythene each night, particularly after heavy rain.
The grubs will come up to the surface and onto the grass, where they can be removed the following morning.