Weird white caterpillar?

Weird white caterpillar?

Observation - Weird white caterpillar? - UK and Ireland. Description: 3 larvae found on an alder tree beside a river. The largest and fluffiest one was about 1.5cm. Very odd fluffy surface.

3 larvae found on an alder tree beside a river. The largest and fluffiest one was about 1.5cm. Very odd fluffy surface.