Lady beetles may appear cute to the human eye, but in the insect world, they are fearsome predators. Considered by farmers to be a helpful pest control tool, lady beetles are welcome neighbors in Adirondack gardening communities. Nonetheless, there are controversial aspects surrounding these voracious insects. This article will describe the biology and taxonomy of the lady beetles, then discuss the multifaceted roles they play in both human and insect interactions.
Many New Yorkers are familiar with the red, round, and shiny lady beetles, but they may not be aware of the reason why they have their unusual name. In the 1690’s, this insect was named after the Virgin Mary, the “lady” that British farmers would pray to when their crops were afflicted by pests. The red coloration of the insect’s hardened outer wings, known as elytra, reminded them of the red cloak commonly worn by Mary in artwork of the time. In fact, all lady beetles are categorized in the family Coccinellidae, a term drawing its origins from the Latin coccinus, meaning “scarlet.” Many lady beetles are red; however, some are yellow, black, orange, pink, and/or white.
The broad diversity of lady color schemes is paralleled by the number of lady species. Of the nearly 6,000 lady species, almost 450 species are found in North America. An exact census of lady beetles in the state of New York is hard to find, although there are several noteworthy native species, including the nine-spotted lady beetle Coccinella novemnotata, two-spotted lady beetle Adalia bipunctata, and the convergent lady beetle Hippodamia convergens.
The nine-spotted lady beetle is the state insect of New York. It was elevated to this status in 1989, after a lengthy political process. In 1980, a fifth-grade student name Kristina Savoca petitioned her State Assemblyman, Robert C. Wertz, to designate the charismatic species. With the support of Cornell University’ Entomology Department, the beetle was eventually adopted. By comparison, New Hampshire, Ohio, Massachusetts, and Delaware have chosen the lady beetle as their state insect, without indicating a particular species. Tennessee claims two state insects: the lady beetle and the firefly.
The nine-spotted lady beetle has become rare in New York, and disappeared from the surrounding states. Declining nine-spotted lady beetle populations cause concern for entomologists, who recognize the important ability of this insect to eat aphids, whiteflies, and other devastating pests. The reasons for the decline are unknown; however, some suspected causes are habitat fragmentation and degradation, as well as pesticide use.
Fortunately, the convergent lady beetle can also prey upon the same bugs as the nine-spotted lady beetle, and it is far more common than the nine-spotted lady beetle. Whereas the nine-spotted lady beetle is named for the number of spots on its wings, the convergent lady beetle is named because of the two white lines on the front part of its dorsal surface that appear to be pointing towards each other. This region of the insect is called the pronotum. Convergent lady beetles can be purchased from a variety of online retailers. Their slender bodies have a more oval shape than the nine-spotted ladybugs, but their appetites are still ravenous.
There is some debate about the effectiveness of the convergent lady beetle in cooler weather. The two-spotted lady beetle is known to emerge earlier in the spring, perhaps to avoid competition with other lady species. One reason why entomologists are concerned about the biodiversity of lady beetles is because the insects provide pest control services at different times of the year. The loss of one species may allow pest outbreaks that are too large for ladybug species to control later in the year.
Each lady beetle species has a slightly different manner of hunting, but there are some noteworthy similarities. The beetles use olfactory cues given off by insects and plants to find the populations of aphids, whiteflies, mites, or other pests. Once the beetle lands on the plant, they patrol edges of the leaf, using visual and olfactory cues to get closer to their prey. They crawl slowly and turn more frequently when the olfactory cues grow stronger. This behavior prevents them from crawling past the prey items. The rounded bodies of the ladybird beetles protect them from birds, ants, and other predators that may try to attack them while they forage for aphids and whiteflies. Lady beetles use similar strategies when they are larvae, although they are limited by the fact that they don’t have wings until adulthood. In the absence of prey, the larvae may eat each other, or the eggs of their unhatched siblings! Many farmers appreciate ladybugs for their pest control abilities, but not all New York residents give ladybugs a glowing review.
In an attempt to control invasive Asian bugs, the multicolored Asian lady beetle Harmonia axyridis (pictured) was introduced by the USDA to the United States. Native lady beetles were struggling to control non-native bugs, so the scientists wanted to find a non-native beetle to do the job. Despite the ability of this insect to control Asian aphids, some homeowners are upset with the decision because there has been an increasing trend of these ladybugs invading houses. The multicolored Asian lady beetles have been documented congregating in window sills, or in the corners of rooms. It is believed that the invasive beetles are looking for places to overwinter, unlike the native beetles, which overwinter outdoors. In Asia, the beetles congregate in mountains before they go dormant in the winter. Congregating in areas with snowfall helps them stay insulated. When they attempt to congregate inside a house, the warm air reactivates them.
Although official guidelines for removing the beetles are not yet developed, it is recommended that homeowners not damage the beetle. They release pheromones that are noisome, and capable of attracting more beetles to the home. Gently brushing them into soapy water may be a necessary to control tactic. Windex, or similar cleaning products, may break up their residual pheromones, but will not repel additional invasions.
Lady beetles are a major part of Adirondack gardens and farms. Although some of the beetles may be inconvenient for homeowners, many vegetable farmers appreciate their pest-fighting prowess. If you would like to learn more about identifying lady beetles, consider looking into Cornell’s Lost Ladybug Project, an organization that is tracking lady beetles across North America.
Photo: An adult Hippodamia convergens Guerin (Coleoptera: Coccinellidae) eating aphids. Image credit: SABeebe, Copyright © 2009, taken in Tucson, Arizona. This ladybird beetle is found throughout the Adirondack region.