When is the Willow Grub most available to trout?

January–March, typically 11:00–16:00. It picks up from about 14°C, peaks around 19°C and tails off by 25°C.

What flies imitate the Willow Grub?

Willow Grub, Tiny Yellow Grub, Caterpillar, CDC Grub, typically on a #18–16 hook.

How big is the Willow Grub?

Adult stage: 4–6mm. That matches a #18–16 hook.

Terrestrial · Terrestrial

Willow Grub

Euura proxima

Size

4–6mm

Hook size

#18–16

Hatch window

Season January–MarchPeak time 11:00–16:00

Water temperature

19° peak

14°25°

How fish feed on it

Don't picture a winged insect landing — this is a grub, not a fly, smaller than almost anything else in this file at 4 to 6mm, and it never had wings to begin with. It's a sawfly larva that drops out of willow leaves onto the water below on the stillest, sunniest days of the NZ summer, January into March, and once enough of them are in the film trout get fussier than almost any other hatch produces — sipping steadily at something so small it's easy to convince yourself nothing is actually happening. This is the willow-lined water's answer to smutting: match the size, fish it dead flush in the film on a long light leader, and expect the first three flies you try to be refused before the fourth one isn't.

Flies that imitate this

Willow Grub

Tiny Yellow Grub

Caterpillar

CDC Grub

Ecology

Rivers & stillwaterFreestone rivers

Where you'll find this

New ZealandPresent

Present throughout

Identification

Euura proxima is a species of sawfly belonging to the family Tenthredinidae (common sawflies). The larvae feed on the leaves of willows ( Salix species) and was first described by Jean Guillaume Audinet-Serville in 1823.