Celery Leaf Mining Fly
The Celery leaf mining fly (Euleia heraclei) is a pest of celery, parsnip, parsley and lovage. The flies lay numerous eggs which give rise to pale, legless maggots. The maggots then create tunnels in the leaves, causing large blister lines. They eventually pupate either in the leaves or in the soil. Celery fly may be suspected if plants develop blotchy, mined leaves that become brown and papery.
The maggots are most active between early May and autumn, allowing for at least two generations.