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Late Summer Garden Visitors – The Bad and the Good

Get to know a good bug and a bad bug—a garden helper and a destructive thug. They have actually been in your garden all season long, but you didn’t notice them.

In the garden insects that damage crops and ornamentals are considered bad, while pollinators and insects that control pests are viewed as good.

Sometimes insects perform their destruction in full view, other times not. The same is true for the activities of beneficial insects. In view of this it’s useful to watch for indicators of specific insects at work in your garden.

For example, the red headed azalea caterpillar, Datana major, is a principal azalea pest in the Southeast. Its territory ranges from Maryland south to Florida and west to Louisiana. They prefer azaleas as host plants, but they have been reported feeding on blueberries, red oak and andromeda as well.

The adult is an inconspicuous light brown moth with a 2¾ inch wing span. In late spring the females deposit masses of 80 to 100 tiny white eggs on the underside of azalea leaves. The larvae feed as a group on the underside of the leaf until they have completely devoured it. Young larvae have a yellow body with red longitudinal stripes and a black head. They disperse as they mature, moving on to skeletonize and devour more leaves. This incipient damage is your signal to look for the developing caterpillars and control them.

Azalea caterpillars do most of their damage in August and September when the larvae are mature. The caterpillars can quickly defoliate branches or an entire azalea. At this time the two inch long showy mature larvae are easily visible against azaleas’ green leaves. Their head, tail and legs are deep red while the body is black with yellow or white lengthwise stripes.

When disturbed the caterpillars raise their heads and tails to form a characteristic u-shape. That combined with upright hairs on their bodies may seem threatening to humans, but the caterpillars are harmless. They can be safely and easily hand picked off azalea plants.

Insecticidal products that contain Bt (Bacillus thuringiensis) are effective early in an infestation when caterpillars are less than ¾ inch long. Larger worms require a more toxic pesticide such as carbaryl (Sevin 50WP) or cyfluthrin (Bayer Advanced Garden Multi- Insect Killer) for control. Read and follow all label instructions. Remember that you can safely hand pick azalea caterpillars off your plants.

The yellow (aka black and yellow) garden spider, Argiope aurantia, is a garden friend that becomes visible in the late summer garden. The colorful black and yellow or orange spiders are particularly evident this time of year because they have reached mature size and it is mating season.

These spiders are members of the orb weaver family which means that they spin webs in a spiral wheel-shaped pattern. The webs can be up to two feet wide, often with a zig-zag down the center.

We find garden spiders facing downward in the center of their webs waiting for prey to become ensnared. Once an insect is caught and secured the spider injects it with venom and spins a cocoon around it. The spider eats its victim later.

Garden spiders produce venom which they use to subdue their prey. If threatened they will bite defensively. Unless a person is allergic to the toxin, the bite is no more dangerous than other common insect bites.

A male may build a small web nearby the female, or perhaps, even attached to her web. He courts the female until she allows him to impregnate her; and yes, she is likely to eat him when he has finished. The female lays her eggs and wraps them in a cocoon for protection. She guards them until she succumbs to freezing temperatures.

Females produce one to four cocoons. In early spring 500 – 1000 tiny spiderlings hatch from each one. Spiders that survive cannibalism and predation reach maturity in late summer and repeat the life cycle.

Meanwhile, throughout the summer the growing spiderlings eat mosquitoes, flies and other small insects in our gardens.

Enjoy looking at garden spiders’ bright colors, their markings and the intricacies of their webs, but don’t destroy them or their webs. They are good bugs that don’t damage crops and ornamentals.

Reach Debbie Menchek, a Clemson Master Gardener, at dmgha3@aol.com.

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