Many people commonly confuse Asian lady beetles with native ladybugs, often wondering if the presence of one harms the other. While both insects are known for consuming aphids, their relationship is more complex than a simple shared diet.
Telling Them Apart
Distinguishing between Asian lady beetles (Harmonia axyridis) and native ladybugs is the first step in understanding their interaction. Asian lady beetles exhibit a wide range of colors, from orange to red, and can have varying numbers of black spots, or even no spots at all. They are generally larger, typically ranging from 5 to 8 millimeters in length, compared to common native ladybugs which are often 3 to 7 millimeters.
A key identifying feature of the Asian lady beetle is a distinct black “M” or “W” shaped mark on the white area behind its head, known as the pronotum. Native ladybugs, in contrast, usually have a black pronotum with two small white spots or markings that do not form an “M” or “W.” Additionally, Asian lady beetles often have reddish-brown legs, while many native ladybugs have black legs. Behaviorally, Asian lady beetles are known to gather in large numbers inside homes during the fall seeking shelter for overwintering, a behavior less common in native species.
How Asian Lady Beetles Affect Ladybugs
Asian lady beetles significantly impact native ladybug species through direct predation and resource competition. They are aggressive predators that consume the eggs, larvae, pupae, and even adult forms of native ladybugs.
Beyond direct predation, Asian lady beetles outcompete native ladybugs for food sources like aphids and for suitable habitats. Their higher reproductive rates and more aggressive nature give them an advantage in securing prey, leaving less food for native species.
Consequences for Native Ladybugs
The aggressive nature and predatory habits of Asian lady beetles have led to substantial decreases in the populations of several native ladybug species. For example, research indicates that as Asian lady beetle populations increased, native species declined significantly.
The reduction of native ladybugs can disrupt local ecosystems, impacting natural pest control and biodiversity. Asian lady beetles were originally introduced as a biological control agent for pests like aphids, but their spread has inadvertently caused ecological imbalances. As a result, the Asian lady beetle is now considered an invasive species in many regions, despite its initial beneficial purpose.
Managing Asian Lady Beetles
For homeowners, managing Asian lady beetles typically involves preventing them from entering structures. Sealing cracks and gaps around doors, windows, and utility entry points can help keep them out. Repairing damaged window or door screens is also important to block access.
If Asian lady beetles do get inside, gentle removal methods are recommended. Vacuuming them up and emptying the vacuum contents away from the home is an effective way to remove them without crushing them, which can release a foul-smelling, yellowish fluid. It is important to distinguish them from beneficial native ladybugs before taking action. Widespread use of pesticides is generally not advised, as these can harm non-target organisms, including native ladybugs and other beneficial insects.