Plants affected Various
Main symptoms Roots and stem bases are eaten
Caused by Caterpillars of a moths in the family Hepialidae
Timing All year
What are swift moth caterpillars?
- Swift moth caterpillars are the larvae of moths in the family Hepialidae
- They live in the soil and tend to feed on plant roots and at the base of plant stems especially herbaceous perennials
- The species that most often cause damage in gardens are the common swift (Hepialus lupulinus) and ghost swift moths (H. humuli)
- The caterpillars grow to around 45mm long they are usually creamy-white in colour with brown heads. They have three pairs of legs at the head end and five pairs of clasping prolegs on their abdomen and are found often feeding in groups
- Cutworms can cause similar damage but these caterpillars are usually dirty greyish-brown in colour.
- Adult swift moths lay their eggs during mid-summer and scatter there eggs whilst in flight, unlike most moths which land to lay their eggs
- The larvae take one or two years to complete their development
- The adult moths prefer to lay eggs where there is a dense vegetation cover, for example they often occur in the larger numbers where turf has been dug up to make a vegetable or flower bed, large populations tend therefore to be temporary
- Where possible tolerate populations of caterpillars, as butterflies and moths are an important part of the garden ecosystem
- Encourage predators and other natural enemies in the garden such as birds, wasps, hedgehogs and ground beetles. Cultivation of the ground can briefly expose the grubs to predators, such as birds.
- Remove larvae of from soil as they are found
A mixture of nematode species for controlling caterpillars and some other vegetable pests is sold as Fruit and Vegetable Protection and is available from some biological control suppliers. To be effective the nematodes need to be watered into moist soil while soil temperatures are in the range of 12-20ºC (54-68ºF). These temperatures occur between April and September. Nematodes should be applied as soon as possible after purchase, following the suppliers’ instructions. It may be necessary to water the soil before and after application to ensure the soil is sufficiently moist for nematode activity and survival. Repeat application may be necessary.
Biological control suppliers (pdf document)
The RHS believes that avoiding pests, diseases and weeds by good practice in cultivation methods, cultivar selection, garden hygiene and encouraging or introducing natural enemies, should be the first line of control. If chemical controls are used, they should be used only in a minimal and highly targeted manner.
There are currently no pesticides available to home gardeners for the treatment of soil.
The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.