The unwelcome garden visitors that come back every year. Here's a rundown of who they are and how to send them away. Slugs. These garden molluscs, along with their close relative the snail, are one of the most elusive pests in the vegetable patch. At night time they feed on most crops; damaging foliage, roots, stems and bulbs before retreating out of sight in daylight. It is possible to hunt for them with a torch at night while they are active. Beer traps, copper barriers and organic ferrous phosphate based will have some impact while encouraging birds and frogs to the garden, their natural predators, will help to keep the population at bay. Cabbage White Butterfly. The caterpillar of the cabbage white can cause extensive damage to all brassicas, stripping leaves and tunnelling into roots. Vigilantly remove caterpillars and eggs and protect plants with netting or mini polytunnels. Encourage predatory birds by hanging feeders nearby. Rodents. Mice and voles are active all year round and will feed on germinating seeds, plant stems, tree bark and stored produce. Trapping or the introduction of a cat will discourage them. The use of poison can have a detrimental effect on other wildlife. Carrot Fly. The fly larvae tunnel into the roots of carrots, parsnips and celery rendering them inedible and prone to rot. The low flying insect can be deterred by using 2ft/60cm mesh or polythene screens. Planting onions or other strong smelling plants nearby will mask the carrot smell which attracts the fly. Aphids. Aphids such as greenfly and blackfly form huge colonies which can damage the stems and foliage of most plants. Ladybirds and wasps are their natural predators but more effective results can be achieved by spraying with any of a number of organic or chemical insecticides. Wireworm. The larvae of click beetles are laid into the soil in late spring and when grown cause damage to roots and tubers, particularly potatoes. There is no treatment for this pest and preventative action is by inspection and removal. Turning the soil to expose the wireworm to other predatory wildlife is recommended. Allium Leaf Miner. Onions, garlic, shallots and leeks are susceptible to this species of fly. The adult fly and maggot cause damage to the foliage and bulb, leaving it prone to rot and fungal infection. If an outbreak is suspected the young plants should be protected with fine mesh netting in spring and autumn. Whitefly. A number of species of tiny fly larva feed on plant foliage, leaving a sticky deposit which can cause mould. Regular spraying with a soapy solution and encouraging the presence of spiders will help to curtail them. Red Spider Mite. Greenhouse plants are affected by this sap-sucking insect causing damage to foliage. Frequent applications of soapy fatty acid solutions will help control the spread of the mite. Cutworms. The hungry moth larva feed on the roots and stems of vegetable plants in mid to late summer. Cultivate the soil throughout the season by hoeing and weeding to prevent further pupation and expose the larvae.