yellow headed hazel sawfly

yellow headed hazel sawfly

Observation - yellow headed hazel sawfly. Description: One of the caterpillars in the third photo has a yellow head but retains the black pigment in the body.Can anyone give me any information about this.I observed these caterpillars for a few weeks until one day they were all gone.Were they eaten or do they

One of the caterpillars in the third photo has a yellow head but retains the black pigment in the body.Can anyone give me any information about this.I observed these caterpillars for a few weeks until one day they were all gone.Were they eaten or do they all go to pupate on the same day.