Spiders are beneficial organisms that help control pest insect populations and are an important part of a balanced ecology. Spiders have an undeserved bad reputation, and many people are afraid of them. Their presence abounds in nature and the garden where their insect prey live. Limiting insects is the best way of limiting spiders. Aromatic plants with essential oils are effective against many insects.

...
Garden spiders perform an essential service as pest exterminators.

Spider Controls

Spider prevention in the outdoors could cause a spike in nuisance insects, which means problems for your plants. Pesticides are not normally effective on arachnids because they are quick and hard to catch. Sticky traps work, but are nonspecific and catch beneficial insects as well. Cleanliness is the best spider control. Remove debris around the house and keep lawns and weeds down. This reduces hiding places for both the spiders and their food.

Mosquitoes

Eucalyptus is a family of trees and large shrubs native to Australia. They are primarily warm-season plants with moderate frost tolerance. The eucalyptus has a volatile oil that is used as an insect repellent. The oil is pungent and strong in flavor. It is useful as an aromatic and repels mosquitoes as well as other bugs. Peppermint, lemon balm, tea trees and marigolds are also recommended as mosquito repellents.

Osage Orange

Osage orange repels spiders. It is a commonly recommended plant for areas where large pest spider populations are found. The bush is sometimes called hedge apple and produces an interesting-looking fruit. The fruit has skin with oil compounds that smell citruslike. There are chemical compounds in the fruit itself that repel insects, but the tree does not have a repellent effect. Cut open the fruits and place them around the windows to repel insects and spiders.

Herbs and Flowers

Herbs are common companion plants that help control insects and provide other benefits to their neighboring plants. The strong oils in herbs are the controlling agent. Most of the common herbs have insecticidal or repellent properties. These would include: basil, coriander, fennel, oregano, lavender, mint and rosemary. Garlic is effective against aphids, borers, spider mites and many other insects. To protect areas where you are not growing herbs, crush the leaves and scatter them or place them in dishes around the porch or patio perimeter. Flowers with pyrethrins are natural insecticides. These are found in chrysanthemum varieties. Painted daisy, rue, tansy and wormwood also have natural insecticidal powers.