Since woodlice are terrestrial gill-breathing animals, moisture is essential for them, and it is in moist places that they abound. They depend upon a mixed diet, being carnivorous, as well as herbivorous; though normally scavengers, their attacks upon seedlings and tender parts of plants bring them into the ranks of important garden pests.
Woodlice hibernate under any convenient shelter; in the spring, eggs are produced and carried by the female on the under side of the body until the young woodlice hatch. During growth the cuticle or shell is periodically cast, and a freshly-moulted woodlouse is white in colour.
The best method of control is garden sanitation, all rubbish likely to harbour the woodlice being removed. Since they are nocturnal, the woodlice can be trapped by means of moss laid on the ground; the moss in which the woodlice have taken shelter is collected during the day and burned, or immersed in hot water to kill the animals, when it can be used again. Some good results have been secured by means of sliced potatoes dipped in arsenate of lead or Paris green; the potatoes are placed within reach of the woodlice, which are attracted to and feed upon the poisoned bait. Horse manure should not be used in seed beds likely to be infested by woodlice.
Millepedes.
Millepedes are short, worm-like animals, with a fringe of numerous short legs on each side ([Fig. 13], 13), and have a characteristic habit of curling up when disturbed. Though scavengers for the most part, feeding upon decaying vegetation and on small organisms, they may do considerable damage to sprouting seeds, seedlings, and to tender plants; they are particularly abundant in damp and warm soil, where there is an abundance of rotting vegetable matter.
Having a keen sense of smell, millepedes are readily attracted to poisoned bait in the form of sliced potato spread with Paris green: another method is to place a piece of freshly-cut potato under an inverted flower pot, to which the millepedes will be attracted, when they can be collected and destroyed. A satisfactory control measure is to treat infested soil with black-leaf 40, using one part in one thousand parts of water.
Slugs and Snails.
Plants are very often greatly damaged by the depredations of slugs and snails; frequently young plants are devoured as soon as they appear above ground. These animals attack the plants after nightfall, and during the day seek cover. Though slugs will shelter in the soil, they, together with snails, will shelter in any convenient place, such as under old boards, sacking, bricks and stones upon the ground, or under large leaves or amongst rank herbage—indeed, in almost any place that affords cover and moisture. Slugs and snails are especially active during wet weather, and at such times, owing to the overcast conditions, they will continue their depredations in the daytime.
Though slugs are active throughout the year, and even during winter when the temperature is favourable, snails pass the winter, as well as hot, dry spells in summer, in a dormant state, often being found together in sheltered positions where the conditions are dry.
Both slugs and snails copiously secrete a slimy substance, that affords them protection against chemicals used for purposes of control. In the case of the slug ([Fig. 13], 14), the shell is small and inconspicuous, but the large spiral shell of the snail ([Fig. 13], 15) affords the animal adequate protection, into which it withdraws itself in times of danger. Both slugs and snails reproduce by means of eggs; these are white, spherical and opaque, and are deposited in the soil or under decaying vegetation.