This appears to have been a very good year for ladybugs. These familiar insects, known as ladybugs, ladybirds, lady beetles or coccinellids, are among the most beloved of all insects. That is, however, until large clusters appear in unexpected places, including on or in the house. Then, like many other harmless, "outdoor" insects, they become an annoyance and a pest.
Clusters or aggregations of lady beetles are common in the fall and winter. The adults of several common species spend the winter in groups in protected areas such as under leaf litter or loose bark, in tall grass, or inside buildings. In the spring, they resume activity, then mate, and disperse to look for prey and places to lay their eggs.
There are over 5000 different species of lady beetles in the world, approximately 475 species in North America, and up to 100 different kinds of lady beetles in Iowa. Adult lady beetles are characteristically oval or round and "dome-shaped" with distinctive spots and markings on orange, red or black backgrounds.
The most common and most familiar include the following.
- Twelvespotted lady beetle , Coleomegilla maculata. Approximately 1/4" long (5-6 mm); oval; pink to red with six spots on each wing.
- Convergent lady beetle , Hippodamia convergens. Approximately 1/4" long (4-6 mm); oval; red with up to 13 spots; prominence of spots is variable; two white lines behind the head "converge" toward each other.
- Sevenspotted lady beetle , Coccinella septempunctata. Approximately 1/3" (7-8 mm); round; red or orange with seven black spots (three on each wing and one at the top). This imported species from Europe and Asia was first found in Iowa in 1985.
- Asian lady beetle, Harmonia axyridis. Approximately 1/3" (6-8 mm); oval; pale orange with 19 black spots (spots may be faint or missing). There is a white, letter "W" shaped mark on the thorax.
The "Asian lady beetle," is included because of its status as a new species in Iowa. It was introduced to the U.S. from Asia and has been common in many areas of the eastern U.S. for the past several years. As a biological control, the Asian lady beetle is a beneficial inhabitant of the garden. However, it is a serious household pest (accidental invader) in those areas where it has become well established and abundant.
Asian lady beetles were first found in Iowa in 1994. The species has now been confirmed in 6 counties. See the March 22, 1996 Horticulture and Home Pest News for additional information on this species as household pest. As with other accidental invaders, the most effective management option will be to prevent invasion by sealing cracks, gaps and openings on the outside before the beetles wander in during late summer. Homeowner perimeter spray treatments have limited effectiveness. PCO-applied sprays of wettable powder, residual pyrethroids have been showing some promise as preventive treatments. Indoor sprays will be no benefit. For now, the practical solution is for homeowners to vacuum and discard invader lady beetles as they appear.
We are documenting the distribution of this new species within the state. Please submit samples (several specimens, if possible) that you suspect of being Asian lady beetle to:
Insect Diagnostic Clinic
Department of Entomology
Iowa State University
Ames IA 50011
This article originally appeared in the November 8, 1996 issue, pp. 172-173.