You may have noticed droppings on your car, or on the sidewalk. You may have thought you heard the sound of rain on a clear day. Both of these things are caused by a caterpillar that is making its way across the state.
Jim Northum, Arkansas Forestry Commission Forest Health Specialist, said parts of central Arkansas are experiencing an outbreak of the variable oakleaf caterpillar (Heterocampa manteo). This common insect ranges from Eastern Canada to southeastern states, like Arkansas and Missouri. Infestations can cover millions of acres. Northum said the heaviest damage has been seen in the Mayflower-Conway area and many reports have been received from West Little Rock.
Fully grown larva are 1 inches long and vary in color from green to yellow, with a pink or dark red stripe on the back, depending on population. If the caterpillar population is low, they are usually pale green, while high populations have red stripes.
Larvae feed on the foliage of deciduous trees, including all species of oak. Most damage in central Arkansas seems to be on red oaks. The major damage is unsightly defoliation as the larvae eat the leaves down to the main veins. Feeding caterpillars make a mess on decks, patios and in swimming pools. Falling frass sounds like sleet peppering in dry leaves. Infestations normally do not last longer than two years. Normally trees are not killed. However, defoliation adds another stress factor to trees already stressed by the past two dry summers. Weakened trees are more susceptible to attack from borers and diseases.
Northum said two generations can occur in Arkansas. The first generation feeds until June or July before pupating in cocoons. Second generation larvae feed in late August and early September. Leaf litter is the wintertime home to the pre-pupae cocoon until pupation occurs in spring. These pink to red pre-pupae are reputed to be an excellent trout bait. Chemical control is not recommended for most situations. Natural control by parasites and predators may destroy as much as 90% of the eggs and larvae. By not using pesticides these parasites and predators can develop fully and do their jobs of controlling the caterpillars.