Q Are centipedes and millipedes garden pests?
A Centipedes are not garden pests at all. They do not attack plants, feeding instead on small soil animals and slugs. Millipedes feed mainly on decaying plant material, but they can also damage seedlings, bedding plants, peas, beans and carrots, for example, and soft tissues, such as cucumber plants, strawberry fruits and tomatoes. They usually prefer to enlarge wounds already inflicted by slugs, wireworms or other pests, in potatoes and bulbs, for example. Their mouthparts aren’t strong enough to deal with undamaged bulbs and tubers.
Caption: Centipedes and millipedes like damp, dark places
Q How do I know if they are actually causing the damage?
A There is no way to be sure. Millipedes tend to nibble stems, aerial roots and growing points. If you have controlled slugs, snails and wireworms and only soft or young tissue has been attacked, these pests may be to blame.
If firm, older material has been damaged, look for pests like cutworms, wireworms, chafer grubs, leatherjackets and caterpillars. Slime trails are tell-tale signs of slugs or snails.
Q Can they be mistaken for anything else?
A They are pretty distinctive. However, millipedes and centipedes, 2-6cm long, could be mistaken for wireworms (1-2cm long, larvae of the click beetle). However, this pest has legs only at the end near the head.
They can also be confused with symphylids. These are small (9mm) and pale, a bit like young millipedes or centipedes. They are very mobile and are sometimes associated with seedling damage in greenhouses and, very occasionally, in outdoor crops. Typically they strip the root hairs from seedlings, leaving a bare root with blackened spots. They are dealt with in the same way as millipedes.
The little springtails, leaping insects found in soil and plant debris, could be mistaken for young millipedes or centipedes. However, these are typical insects with three pairs of legs, and they are harmless.
Q Why do they always seem to occur in the same places?
A They all like damp and dark places.
Shady damp gardens with plenty of cover under furniture, mulch, containers and plant material are ideal for millipedes. These conditions are hard to modify, and high populations can build up in suitable gardens. Organic mulches, of bark for example, are likely to provide ideal hiding places for millipedes. Heated greenhouses are favoured. Some species are only found in greenhouses.
Q How do I tell centipedes and millipedes apart?
A British species of centipede are golden or chestnut brown in colour, move rapidly when disturbed and have one pair of legs for each body segment. Millipedes move slowly and have two pairs of legs to the majority of body segments. Most of the 48 different kinds of millipede are divided into two groups: flat and pill millipedes.
Flat millipedes have flattened bodies, while the pill millipedes have a rounded, snake-like shape, and move in a similar way to snakes. The flat millipedes, which are greyish-brown in colour, are similar in appearance to centipedes, but have two pairs of legs for each body segment. Another way to tell them apart is to touch them. Centipedes run away, whereas millipedes curl up.
Q Are there any similarities between millipedes and woodlice?
A The pill millipedes can look very like the grey-coloured pillbug-type of woodlouse, but the snake millipede is the one that causes damage to plants most often. The spotted snake millipede (Blaniulus guttulata) is about 18mm long, creamy-white in colour with a row of orange-red dots along either side of its body. Both types of millipede can roll themselves into a ball when disturbed. Another distinguishing point is that woodlice have only seven pairs of legs.
Q Where are millipedes most likely to be found?
A Millipedes are most likely to be found on the surface of the soil, except in dry weather when they will burrow further down into damp soil. Female millipedes lay eggs in summer, often in nests. These hatch into larvae which, after several intermediate stages, reach adulthood, the whole cycle taking a year or more. In greenhouses, the glasshouse millipede (Oxidus gracilis) is sometimes found. It is an introduced species that only thrives in heated greenhouses.