Ladybugs Vs. Japanese Beetles: What You Need To Know
Ladybugs and Japanese Beetles are two of the most commonly encountered insects in the eastern United States. Often found in the same location, naturalists recognize them easily.
Ladybugs gleam bright red with black polka dots and race along the stems and twigs of plants. Japanese Beetles display lustrous metallic bronze and green colors and rest quietly on plant leaves.
But if you wonder how they differ beyond just their looks, this post will help!
Ladybugs are small, carnivorous beetles native to the United States and helpful to humans. Japanese Beetles are large, herbivorous beetles accidentally introduced into the United States and significant pests. There are many species of “ladybugs” but only one species known as “Japanese Beetle”.
Both are insects within order Coleoptera but classified in different families; ladybugs to family Coccinellidae and Japanese Beetles to family Scarabaeidae.
Read on to learn more about some of the significant differences between these two insects and why they matter to us.
There are many “ladybugs” but only one “Japanese Beetle”
People apply the informal term “ladybug” to many small insects that share the basic “beetle” body type. This includes those animals with brightly colored, dome-shaped backs whose wing sheaths meet in the center of their backs. Also known as “ladybirds” and “lady beetles”, more than 5,000 species of ladybugs live worldwide. Approximately 480 of those species live here in the United States.
In contrast, “Japanese Beetle” refers to a single, specific species, at least here in the United States. The insect’s scientific name is Popillia japonica. While classified within family Scarabaeidae along with more than 30,000 of its beetle cousins, the informal name “Japanese Beetle” applies to no other insect.
Ladybug larvae are carnivores; Japanese Beetle larvae are herbivores
All ladybug larvae are carnivores, and pretty fearsome ones at that (Cranshaw and Shetlar 2017). An encounter with ladybug larvae means big trouble for any smaller animal. Prey includes spider mites, caterpillars, grubs, and even other ladybug larvae.
These creatures actively crawl around on plants and attack any prey they can find. Some species of ladybug larvae prefer certain prey species. But for the most part, they don’t pick and choose between prey species very often. Ladybug larvae hunt opportunistically. They attack any creature they can safely overcome.
Ladybug larvae must consume a lot of energy to develop through the larval stage and metamorphose into the adult ladybug form. In fact, ladybugs eat more insect prey as larvae than as adults (Cranshaw and Shetlar 2017). They consume any prey too weak to fend them off.
On the other hand, Japanese Beetle larvae live differently in every way.
Japanese Beetle larvae are all herbivores. They live under the soil as pale white grubs with yellowish brown heads and three pairs of short, jointed legs. They wriggle their way through the soil until they find suitable plant roots and then dig in, munching quietly away in their subterranean world.
Ladybugs move a lot faster than Japanese Beetles
Japanese Beetles crawl slowly; their lifestyle as plant-eaters didn’t demand that they evolve great speed. Ladybugs, on the other hand, can move fairly quickly, given their size. Here is a video that shows a ladybug moving across an oak tree leaf.
Some ladybugs change their behavior as they age; Japanese Beetles don’t
Many people – especially those who garden – are aware that ladybugs are predators. Ladybugs have a great reputation amongst anyone who has ever tried to grow roses or a vegetable garden because they eat huge numbers of aphids, which are one of the major plant pests that gardeners battle.
As noted above, all ladybug larvae are predators – 100% of ladybug species actively hunt prey when they are young. But a strange thing happens to some species when they metamorphose from their larval form to their adult form. They change from pretty impressive predators to completely nonthreatening plant or fungus eaters.
While most adult ladybugs preserve the predatory lifestyle they had in their larval stage, some species of ladybugs emerge from the pupa to feed on leaves, pollen, flower nectar or fungus. It’s a complete change in lifestyle that often goes unremarked.
On the other hand, Japanese Beetle behavior is consistent across their lifespan. They start and end their lives as herbivores.
Despite massive changes in their body forms from larval to adult, they always eat plants. The grubs start damaging plants from their underground position, attacking delicate plant roots and interfering with the plant’s ability to absorb nutrients.
Once the beetle larvae pupate, they dig themselves out of the ground, crawl or fly onto the plant’s leaves and start chewing.
Japanese Beetles are as voracious in their eating habits as ladybugs and can do tremendous damage to a plant in a short period of time. They “skeletonize” leaves by eating the soft tissue from between the veins, which drastically reduces a plant’s ability to photosynthesize.
Do ladybugs eat Japanese Beetles?
Since ladybugs are predators that attack creatures that feed on plants, and Japanese Beetles are creatures notorious for feeding on plants, you might wonder if ladybugs attack Japanese Beetles.
Ladybugs do not attack Japanese Beetles because the beetles are much bigger than the ladybugs. Japanese Beetles are about the size of an American quarter coin (18-29mm or 0.7-1.1in), with females usually being larger than males.
Ladybugs species range in size from 1-10mm. One of the most common North American species, the Convergent Ladybug (Hippodamia convergens) is only about the size of pencil eraser (4.5-6.5mm or 0.18-0.25in).
If a Japanese Beetle were weakened in some way, a ladybug might consume it as an opportunistic meal. But in general, Japanese Beetle grubs are safe from ladybugs because they live in the ground and the adults are safe because of their size, even if both exist in close proximity on the same plant.
Ladybugs have defenses against predators; Japanese Beetles don’t
Ladybug defenses
Ladybugs have specific anti-predator defenses.
Their bright coloration is not sheer ornamentation. Rather, it serves a life-and-death purpose and is referred to as “aposematic coloration”.
Their bright red and black polka-dotted pattern serves as a visual warning to predators. Ladybugs accumulate toxins in their bodies that make them taste unappealing to predators. In some cases, the toxins can sicken or even kill predators.
Many insects other than ladybugs exhibit “aposematic coloration”. Some species are just bluffing. But not ladybugs. The warning ladybugs send out with their bright colors is legitimate.
Ladybugs have another trick to keep from being eaten by predators too naive to avoid them. When under attack, ladybugs ooze a foul-smelling and tasting liquid from their leg joints. This defense tactic is called “reflex bleeding” and is displayed by several different insect families.
Predators must be small enough and sensitive enough for this liquid to deter an attack because ladybugs are small insects themselves. But even human noses can detect the pungent, unpleasant odor manufactured by certain ladybug species.
Predators who fail to heed the visual warning and attack ladybugs learn their lesson the hard way. While no defense in nature is 100% effective, ladybugs’ reflex bleeding deters even especially dangerous predators like spiders much of the time. They usually look elsewhere for future meals.
Japanese beetle defenses
In contrast, Japanese Beetles never evolved reflex bleeding and so are more vulnerable to predation than ladybugs.
While relative size protects Japanese Beetles from predation by carnivorous ladybugs, they aren’t so lucky when it comes to other predators.
Japanese Beetles are on the menu for a large variety of bigger predators, including birds, skunks, raccoons, moles, spiders, lizards, two species of tiphiid wasps and one species of tachinid fly (Held and Potter 2009).
As with many insects, the beetles ensure survival into the next generation primarily through sheer numbers, not through any special talent for escape or defense. An adult female will lay 40-60 eggs in a reproductive season (Held and Potter 2009). But this only supports the population as a whole. A single, unlucky Japanese Beetle can be eaten at any time.
Ladybugs are heroes; Japanese Beetles are pests
Ladybugs, agricultural heroes
Ladybugs enjoy one of the best reputations of any insect group because they are effective predators of aphids and other garden pests,.
Gardeners are generally happy to see ladybugs amongst their plants and several experiments that introduced ladybugs as biological controls to reduce pest populations have been very successful.
One famous example of introducing ladybugs as biological pest controls happened in California in 1889. A species known as the Vedalia Ladybird Beetle (Rhodolia cardinalis) was released to eradicate the cottony-cushion scale insect which had infested the citrus groves after being accidentally imported from Australia. (Lagasse 2018)
While still recognized for their value in pest control, ladybugs have lost some of their popularity as biological control agents in recent years. In some areas, they are actually considered pests.
This is due in large part to the Asian Ladybug (Harmonia axyridis).
Also known as the Harlequin Ladybug, it was introduced to the United States to control agricultural pests but now causes problems the scientists didn’t anticipate. In particular, they have a habit of swarming and overwintering in gigantic groups within buildings.
Huge numbers of these ladybugs have infested homes and businesses in recent years. Beyond the distress that large numbers of insects invading a living space can cause humans, the reflex bleeding exhibited by these insects stain walls, furnishing and clothes. Additionally, many people are allergic to them and some severe reactions have been reported.
Japanese beetles; universal villains
On the other hand, very few people have ever admired Japanese Beetles or wanted them around.
They are widespread across the eastern and central United States – especially the northeastern portion – and they spread to this current distribution all on their own.
No one knows for sure how Japanese Beetles arrived in the continental United States from their native Japan but it was surely by accident. Scientists think that some of the beetles or eggs hitched rides within nursery plants imported from overseas to the U.S around 1916.
Regardless of how they arrived, there is no doubt that the beetles found their new home much to their liking.
“By 2007, the beetle was established in all states east of the Mississippi River except for Florida, and in the central United States as far west as Minnesota, Nebraska, Kansas, and eastern Colorado. It also has spread north into southern Ontario and Quebec, Canada, and is established on Terceira Island (Azores, Portugal) where it escaped from a U.S. air base.” (Held and Potter 2009)
(Held and Potter 2009)
Every year, hundreds of millions of dollars are spent across the United States trying to control the population and limit their spread (Held and Potter 2009), with varying degrees of success.
Overall, ladybugs continue to be much more popular than Japanese Beetles. However, experts now consider the possible introduction of ladybugs as biological controls more cautiously and ladybugs are not as universally beloved as they once were.
Despite being cousins within Order Coleoptera, ladybugs and Japanese Beetles are very different insects. The fact that the natural behavior of one is more helpful to humans than that of the other is mere happenstance – a lucky one for the ladybugs, an unlucky one for the Japanese Beetles.
References
Cranshaw, Whitney and Shetlar, David, 2nd ed. 2017. Garden Insects of North America. Princeton University Press.
Held, David W. and Potter, Daniel A. 2nd ed. 2009. Japanese Beetle; Encyclopedia of Insects. Elsevier Science & Technology.
Lagasse, Paul. 8th ed. 2018. Ladybird beetle; Columbia Encyclopedia. Columbia University.
