Catalpa Hornworm
Need to know
- Catalpa hornworms are black and yellow with a prominent, yet harmless horn at the tail end.
- They produce one to two generations per summer.
- The damage, even near-complete defoliation, is of relatively minor significance to the trees.
- Spraying is not advised, especially late in the season, and if most of the caterpillars have reached full size it does more harm than good to spray.
Description of catalpa hornworms
Some catalpa hornworms, also known as catalpa sphinx larva, are black with yellow markings, while others look yellow with black markings. Both have a prominent, harmless horn at the tail end. There may be tremendous variation in size and appearance. The full-grown length is almost 3 inches.
Life cycle of catalpa hornworms
There are 1 or 2 generations per summer but the large caterpillars in late summer are the only ones generally noticed.
Damage caused by catalpa hornworms
The damage, even near-complete defoliation, is of relatively minor significance to the trees. Trees withstand infrequent defoliation without lasting harm. Buds are not hurt and trees re-leaf the following spring as if nothing happened. This caterpillar is more annoying than damaging. The full-grown caterpillars crawl from the tree and cover the sidewalk, patio, etc. and annoy (but without really hurting anything). Fecal pellets are an unpleasant nuisance. Try to think of them as free "fertilizer."
Management of catalpa hornworms
A parasitic wasp attacks the caterpillars when they are numerous. The parasites live inside the caterpillar for several weeks and then emerge to form white cocoons that protrude from the back of the caterpillar.
Spraying is not advised, especially late in the season. If most of the caterpillars have reached full size it does more harm than good to spray. The trees withstand the defoliation, the insecticides are destructive to parasites and other beneficial insects, the caterpillars are difficult to kill and the damage to the tree has already occurred.
Do you live in Iowa and have an insect you would like identified?
The Iowa State University Plant & Insect Diagnostic Clinic will identify your insect, provide information on what it eats, life cycle, and if it is a pest the best ways to manage them. Please see our website for current forms, fees, and instructions on preserving and mailing insects.
Contact information for each state's diagnostic laboratory for U.S. residents. If you live outside of Iowa please do not submit a sample without contacting the Plant & Insect Diagnostic Clinic.
Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Yard and Garden, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on September 12, 2016. The information contained within may not be the most current and accurate depending on when it is accessed.