Ladybugs are a beneficial group of insects that help farmers and gardeners by eating aphids and other insects that are dangerous to plants. However, there are some species of insects that look like the common ladybug, but they have different physical and behavioral characteristics. Not all of these insects are beneficial to gardeners, and some can be destructive.
Multi-Colored Asian Lady Beetle
The multi-colored Asian lady beetle goes by a variety of names, including the Asian lady beetle, the Halloween beetle, and the Ladybird beetle, among others. These insects are easily confused with ladybugs because they are approximately the same size and shape, but there are several distinct differences between Asian lady beetles and ladybugs. Ladybugs are small, dome shaped insects with red or orange bodies and black spots. They are beneficial to gardens and crops because they feed on aphids, which are parasitic insects that can kill garden plants. Asian lady beetles can be tan, orange or red, and they have a distinctive 'm' or 'w' pattern on their heads that distinguishes them from ladybugs. Asian lady beetles are helpful to plants because they also eat aphids, but unlike ladybugs, they swarm and can be a nuisance during the colder months when they want to come indoors. Just before dying these insects emit a foul odor and release a yellowish fluid that can stain walls, floors or carpeting. (see references 1 and 2)
Squash beetles are a member of the lady beetle family, and they look very similar to ladybugs in shape and coloring. Ladybugs, however, are a great deal smaller. Ladybugs are usually only about 1/4 of an inch in size, but squash beetles are closer to 3/8 of an inch long. Squash beetles have similar coloring and are usually orange or red with black spots. Unlike ladybugs, these insects are not beneficial. Both the larvae and the adults feed on the leaves of various types of squash and melon plants including zucchini, pumpkin, cucumber and watermelon. This interferes with the plant's ability to photosynthesize sunlight and will eventually kill the plant. (see reference 3)
Mexican Bean Beetle
Mexican bean beetles are similar in size to ladybugs, and they are usually yellowish-orange in color with eight black spots on each wing. Like the squash beetle, the Mexican bean beetles are a pest species that feed on garden varieties of beans and peas. They lay their eggs on the bottoms of leaves, and both the adults and larvae attack and feed on the leaves as well as the stems and pods of plants. They do the largest amount of damage in mid-to-late summer. (see reference 4)