Extension Educator, Horticulture
Insects congregating in large numbers can be alarming. However packs of wild insects do not necessarily mean the insects are up to no good.
For example, ladybugs will congregate on the sides of trees in late fall. They are not plotting to overthrow the world, but are just looking for several friends to bunk with over the winter. Since ladybugs and their young eat many of our garden pests, we should encourage them into the garden.
Green cloverworm moths are probably fluttering in a lawn near you, especially where lights are left on at night. A walk through the lawn produces a cloud of dark 1-1/2 inch moths that resemble stealth bombers. These moths have been particularly numerous the last few weeks. Their caterpillars, alias green cloverworms, are light green with four faint whitish stripes down their back and are about one inch long.
However, you probably won't see the caterpillars unless you are hanging around soybean, clover or alfalfa fields in July and August. Green cloverworms can be a particular problem on soybeans and cowpeas in the south. Presently the adult moths are just a nuisance in a home landscape.
The adults do no damage. They are not feeding on lawn grass, lawn furniture or clothing. Right now they are probably just looking for a mate. Even if they do mate and lay eggs, the eggs will not survive the winter here. Pesticides are not necessary and should not be used to control this moth. The moths will be killed by the upcoming frost. Each spring the moths have to migrate in from the south.
We normally don't see quite so many green cloverworm moths. Usually the moths would have succumbed to any one of several moth diseases, but the fungal diseases have not been as prevalent as usual because of the dry weather. The good news is don't worry about these moths. Sit back and enjoy the entertainment they provide for bored cats.
Presently another noticeable insect is the fall webworm. These caterpillars feed on a variety of trees, but mainly crabapples, walnut, mulberry and elm. In late July and August caterpillars spin a silken web over the ends of branches. The caterpillars feed on the leaves inside the web. As they feed, they enlarge the web. In late July and August the fall webworm nest can be pruned out and destroyed. When webs are first noticed, sprays of the bacterial agent Bt such as Dipel or Thuricide can be effective. Insects that cause late season leaf loss rarely effect plant health. This time of year I would not worry about fall webworm and watch for infestations next July.