Silk and Venom

In the third post in her series on garden insects, Jean Godawa writes about the benefits of having spiders in your garden.

To me, the beauty of a garden goes beyond the sensory enjoyment it provides. The vibrant colours, varying textures and fragrant air command our attention, but it is the inner workings of the garden, the things happening regardless of our horticultural skills, that make it a special place, worthy of our awe and appreciation.

Spiders are one of those creatures with a significant role in keeping garden plants healthy and they do this with little to no help from us. By eating the bugs that destroy plants, these eight-legged animals are always on duty as pest control agents.

Orb weaving spiders spin silken webs to attract flying insects. One of the most striking of the orb weavers is the black and yellow garden spider (Argiope aurantia). Although its bright colouring and large size make it look somewhat tropical, this species is quite common in gardens throughout the U.S. and Canada.

The female creates a complicated web that can have a diameter of more than 60 cm or 2 feet. She adds zigzag strips, called stabilimenta to the construction. Despite the name, these structures probably don't help stabilize the web. They are more likely used for attraction of prey or mates, or for warning or camouflage. It costs the spider much energy to produce these intricate patterns so they must provide some advantage. Scientists are still trying to figure it out.

Any flying insect is a potential meal for garden spiders including grasshoppers, aphids, wasps, bees and butterflies.

Some spiders prefer to capture their insect meals by ambush methods rather than expending any silk. Crab spiders (Thomisidae), use their larger front legs to easily grab their prey. Some species can change over time to match the colour of their plant surroundings.

A more active hunter is the jumping spider (Salticidae).These creatures pounce on their insect prey using their sharp vision and nimble movements.

Most spiders only live for one season. They lay eggs, usually inside silken cocoon-like structures. In some species the eggs hatch before winter but the young spiderlings remain protected in the silk until they can disperse in the spring.

Spiders feed by injecting venom into their prey to immobilize it. Digestive fluids liquefy the prey and the spider sucks up the remains. Gruesome as this sounds, most spiders are rarely dangerous to humans. They are more likely to escape your presence than to bite you.

Even an arachnophobic gardener can't deny the benefits of welcoming spiders into the garden. Tall grasses and long stemmed plants provide stable support for orb-weaving spiders to construct their webs. Other spiders prefer the dark damp conditions of thick mulch. If a garden provides these habitats, it can be sure of non-stop, natural pest control from spiders.

About Jean Godawa: Jean is a science teacher and writer. She has been writing science-related articles for print and online publications for more than ten years. Jean holds a degree in biology and environmental science with a focus on entomology from the University of Toronto. She had conducted field research in the tropical rainforests of Asia and South America.

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Five Garden Bugs You Need to get to Know

It is my pleasure to introduce you to Jean Godawa, a science educator and writer. Insects may be a tiny creatures, but that is not to say they don't have an important role to play in the garden. In her first post, Jean introduces us to five insects whose role in the garden is highly beneficial. Most importantly, Jean helps us to avoid misidentifying the less familiar larval form of these helpful insects as pests.

One of the hardest lessons for novice gardeners to learn is to embrace the presence of insects in the garden.  Of course we know that there are plant-destroying bugs that can wipe out some of our favourite flora, but there are other creatures that we should be welcoming into our gardens.  Acting as pollinators, predators and decomposers, beneficial insects are the master gardeners and we are just their apprentices.

Lacewing 

The aptly named, faery-like lacewing (Chrysopidae) has an appetite for plant-sucking aphids. Lacewings are common throughout North America and lay their eggs at the end of stalks, usually on the underside of foliage.

Larval form of green lacewing      

In its immature form, as well as adult, predatory lacewings protect plants from herbivorous insects.

Seven spotted ladybug larvae  

Ladybugs, also known as lady beetles or ladybird beetles (Coccinellidae) are one of the most easily recognized garden bugs. Like lacewings they help keep aphid populations in check. Their larvae however, are not so easily recognized and are sometimes mistaken for unwanted pests.

The colouring of these ladybug larvae along with the bright colours of their adult forms, acts as a warning. Ladybugs have a foul taste that protects them from birds, bats and other insectivores.

Hover fly   

The same yellow and black colour provides an advantage to several other insects. It’s difficult to tell the difference between a hover fly (Syrphidae) and a wasp. Up close, you can see that hoverflies, like all flies (Diptera), only have one pair of wings. All other winged insects have two pairs. The colouring mimics that of a wasp which helps guard against predators. Despite this warning, hover flies do not sting.

Hover fly larva on aphid infested plant

Hover fly larvae are predators of tiny plant-eating insects. Adult females hover over plants looking for a place to lay eggs. Plants with aphids, whiteflies or other pests are optimal as they provide a food source for her larvae once they hatch. As adults, hoverflies derive their energy from nectar and, in a small way, act as pollinators.

Braconid Wasp Cocoons on Sphynx Moth Caterpillar

Most of us are familiar with, and probably afraid of, the yellow and black colouring of another insect. Wasps, like hornets and yellow jackets, scare us away from outdoor fun, especially in late summer when they seem to be everywhere. But our bias towards wasps shouldn’t taint the whole group. There are thousands of species of wasps, particularly in the ichneumonid and braconid families that are immensely helpful in the garden and most of them do not sting. Braconid wasps act as control agents for particularly destructive creatures like caterpillars. The adult wasps lays eggs directly onto caterpillars and when the larvae hatch, they eat the caterpillar from the inside out.

Ichneumonid wasps   

Adult ichneumonid and braconid wasps can, in a small way, help pollinate flowers when they visit them for nectar, but it is their parasitizing larvae that are most helpful against pests.

Bumble bee  

Of course we could not discuss black and yellow insects without mentioning bees (Apidae). With their larvae safely protected in nests underground, in tree cavities or other protected spaces, adult bees forage for pollen and nectar throughout the garden. Their feeding activity pollinates the flowers of many backyard trees and garden vegetables, ensuring we have fresh foods like sweet cherries, flavourful herbs, plump tomatoes and Halloween pumpkins.

The recent decline in bee populations, particularly in honeybees, threatens even the smallest vegetable garden. Not only does bee pollination provide food for our table, it ensures that seeds form for future harvests. Create a bee-friendly garden by including their favourite plants, building a bee house and providing a small water source.

Recognizing these master gardeners and being able to distinguish them from unwanted visitors is just one of the important lessons we, as their apprentice, must learn.

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Many thanks to Ken Sproule and David Cappaert for providing images for this post.

About Jean Godawa: Jean is a science teacher and writer. She has been writing science-related articles for print and online publications for more than ten years. Jean holds a degree in biology and environmental science with a focus on entomology from the University of Toronto. She had conducted field research in the tropical rainforests of Asia and South America.