Adult brown tail moths do not pose any threat to human health and may be seen in July and August each year. However, female moths lay a batch of 200-300 eggs on a wide range of trees and shrubs which soon hatch into clusters of caterpillars in late August and early September.
It is the caterpillars which cause problems the following spring as they are covered in tufts of ginger hair which break off if disturbed and can penetrate the skin causing a (sometimes severe) irritant reaction. Asthmatics and hay fever sufferers should not inhale the hairs as they may cause breathing difficulties.
The small caterpillars spin a silken tent over trees and shrubs under which they shelter at night and in cold weather. Caterpillars may be seen from August to October (when they are very small and stay around their web) and then again after winter hibernation from April to June (when they start to leave the web and disperse into surrounding vegetation to find leaves to eat). Small caterpillars are dark brown and have two bright red dots at the end of their body, whereas larger caterpillars are dark grey and hairy with a line of white dots down each side and two red/orange dots at the end of their body. More information on identification of this and other species can be found in the ‘Web-spinning Moths’ Advice Note produced by the Natural Environment Team.
Where large infestations of larger brown tail moth caterpillars occur in the spring, they can cause total defoliation before they move on to other plants. In these circumstances the caterpillars can also cause serious problems to those walking through infested areas or living nearby.
How to get rid of them
Here are some things you can try, and advice:
- get rid of the caterpillars by cutting the tents out from the foliage and burning them or drowning them in a bucket of water
- the best time to carry out this work is between November and March whilst the caterpillars are hibernating, but there are risks involved as many of the irritant hairs from the caterpillars are bound up in the tents and can become detached when pruned out
- if you do attempt to prune out the winter webs, wear strong, protective clothing which is tight at the cuffs and ankles and can be washed or disposed of afterwards. You’ll also need gloves, a hood, boots, goggles and a mask
- don’t deal with an infestation yourself if you are asthmatic or suffer from a skin condition
- if the infestation is too big for you to deal with then you should contact a local pest control firm who will have professional equipment and PPE
- chemical treatments are also effective, but we advise getting a qualified professional to use these. The pesticide pyrethrum is recommended as it does not persist in the environment and is harmless to other wildlife such as hedgehogs which might eat the dead caterpillars.
- if you have an infestation in a tree where legal restrictions apply, such as a Tree Preservation Order or if it is within a conservation area, please contact the Dorset Council Arboriculture Team: firstname.lastname@example.org for advice.
What we are doing
If the moths are causing an infestation on land we manage, please let us know by contacting the Green Space Teams Manager Giles Nicholson: email@example.com or the Natural Environment Team Manager Annabel King: Annabel.firstname.lastname@example.org
Where there is an infestation we:
- carry out targeted removal of webs between November and March while the larvae are dormant
- carry out scrub management where this is appropriate (taking the needs of other wildlife such as protected species, nesting birds etc) to remove caterpillar food plants and therefore reduce the amount of available habitat
- carry out spraying (only with pyrethrum) where the above two options are not appropriate. This is generally only effective in early spring on sunny days when the larvae bask on the surface of their web and therefore come into contact with the pesticide, and isn’t effective once the caterpillars disperse into the wider vegetation
- work closely with town and parish councils, local residents and volunteer groups to co-ordinate web removal and scrub management works
- please note that on Public Rights of Way (PRow), we have a duty to maintain access and consequently manage the vegetation and surface, but in the majority of cases we do not own the land and therefore have no obligation to handle any infestations that arise on or adjacent to the PRoW network.