What is a ladybug?
Lots of things! There are roughly five thousand insect species which we refer to as ladybugs. But for practical purposes, we'll go with Merriam-Webster's summation of what sort of insect we call a ladybug: "any of numerous small nearly hemispherical often brightly colored often spotted beetles (family Coccinellidae) of temperate and tropical regions that usually feed both as larvae and adults on other insects (such as aphids)"

National Geographic's Brief on Ladybugs:
"Ladybugs are also called lady beetles or, in Europe, ladybird beetles. There are about 5,000 different species of these insects, and not all of them have the same appetites. A few ladybugs prey not on plant-eaters but on plants. The Mexican bean beetle and the squash beetle are destructive pests that prey upon the crops mentioned in their names."
"Their distinctive spots and attractive colors are meant to make them unappealing to predators. Ladybugs can secrete a fluid from joints in their legs which gives them a foul taste. Their coloring is likely a reminder to any animals that have tried to eat their kind before: "I taste awful." A threatened ladybug may both play dead and secrete the unappetizing substance to protect itself."

Wisegeek also provides a helpful explanation of what we would consider a ladybug:
"A ladybug is a member of the Coccunellidae family, which includes thousands of insect species. Many people think of bright red beetles with black spots when they hear the word "ladybug," although these beneficial insects can be found in a wide range of colors, with and without markings. Ladybugs live in gardens around the world, and they are often welcome visitors, since they eat agricultural pests like aphids. The distinctive coloration of some species has made them familiar to casual observers, and many societies have myths or songs which feature ladybugs.

Technically, a ladybug is a beetle, not a bug. Other common names for ladybugs include lady birds and lady beetles; the "lady" is believed to reference the seven classic spots on a Coccinella septempunctata, which represent the seven sorrows of the Virgin Mary in some cultural traditions. In addition to classic red, ladybugs can also be found in yellow, orange, green, gray, white, and brown, and some ladybugs have black bodies with colored spots, rather than black spots on a colored body."

Two points of interest here that we'll come back to:
1) Ladybugs come in a variety of colors with or without spots
2) Was the name lady(bug/bird/beetle) really given to the seven-spotted/C7 ladybug as a reference to the Virgin Mary's seven sorrows?

Wait, shouldn't point 3 be that gross liquid that comes out of their joints??
Yeah. Probably. So, when you were a kid you probably held a ladybug and got this gross-smelling, oily yellow-to-redish liquid on your hands. Not a lot, a few little drops. I never knew it came from their joints, I always assumed it came from a gland at the back of the ladybug, so that's surprising information! Some people believe it is the blood of the ladybug, but insects don't have blood, they have a substance called hemolymph and it tends to range from colorless to white to yellowish. So what is this fluid? It's called pyrazine (C4H4N2) and it is excreted by special glands in the ladybug's leg joints. A more detailed chemical study, the result of research into how we can stop ladybugs from ruining wines by tainting the grapes with this foul-smelling compound, has thus far identified thirty-eight different chemicals in the excretion. Three pyrazine compounds seem to be the main culprit for the smell: 2,5-dimethyl-3-methoxypyrazine (DMMP) (C7H10N2O), 2-isopropyl-3-methoxypyrazine (IPMP) (C8H12N2O), and 2-sec-butyl-3-methoxypyrazine (C9H14N2O).

Chemical & Engineering News describes the study:
"The team studied the multicolored Asian ladybird beetle, which invaded the U.S. early last decade. Homeowners encounter the bugs because they aggregate inside buildings for shelter during winter, Cai noted. Wine growers cross paths with them when the bugs feast on damaged grapes in vineyards.

Because humans' odor detection threshold for the odiferous ladybug compounds is so low, "even a tiny amount in the wine will cause a great sensory impact on human tasting," Cai said. "That's why these compounds are so noxious."

The extent of the resulting wine taint problem is unclear, Koziel noted. But "there have been reports of vineyards going bankrupt because entire vintages were lost due to this problem."

Cai began the project by placing ladybugs in a capped glass vial for a day and then collecting the volatile compounds they released. She used gas chromatography and mass spectrometry to separate and identify individual compounds in the mixture. Then, a panel of human "sniffers" told her which of those compounds were the most important contributors to the ladybug scent. Of the 38 compounds identified, Cai determined that 2,5-dimethyl-3-methoxypyrazine (DMMP), 2-isopropyl-3-methoxypyrazine (IPMP), 2-sec-butyl-3-methoxypyrazine, and 2-isobutyl-3-methoxypyrazine play a major role.

The overall smell is a mixture of nutlike, green bell pepper, potato, and moldy odors. At the concentrations present in ladybug emissions, the mixture is "really stinky," Cai said.

The Iowa State researchers are not the first to assess ladybug emissions. But Cai noted that they were the first to discover that DMMP is an important contributor to the odor. "This study also provided the first unambiguous evidence that IPMP is responsible for the characteristic odor of live" ladybugs, Cai said. Koziel added that "we also are the first to observe a correlation between the color of the beetles and the amount of methoxypyrazine found in the air about them." Orange beetles release more of the compounds than do yellow beetles.

Why are the orange beetles worse than the yellow ones?
I don't know yet! I'll get into the colors variations further down, but the pigment responsible isn't mentioned as a culprit. All the ladybugs in the study were the Asian ladybug, so these were morphs, not different species. It could be the gene for the pigment is tied to the gene for the pyrazine compounds, or it could be that the cause of the pigment shift also causes a shift in these chemicals. If I find out, I'll let you know!

Are Asian ladybugs the ones I see? And where did the blood myth come from?
Asian ladybugs propagated since their deliberate introduction to the US in 1916 and have become a dominant species, in part due to being more aggressive than the US's native seven spot ladybug (they will bite you!), and possibly in part due to their high variation in color allowing them to adapt better to climate change. If you see large numbers indoors or otherwise clustering on your windows, this is probably the species you have. The myth about blood seems to come from the fact that the fluid excretion process is called "defensive bleeding" despite the fluid not being blood.

The Ladybug Lady is a good starting to point to learn some basic facts about the Asian ladybug.
If you want more detail, check out the Wikipedia article on Harmonia axyridis. This is also known as the multicolored or harlequin ladybug. Wiki has this very useful image to show just how different members of the same species can look, which also helps to explain why identifying ladybug species can be so difficult!
https://en.wikipedia.org/wiki/Harmonia_axyridis#/media/File:Harmonia_axyridis01.jpg


All ladybugs are Family Coccinellidae, are all Coccinellidae ladybugs?
Yes. All ~5,000 species fall under this umbrella, and this is the umbrella used to describe these thousands of similar species. All of these species are beetles and not true bugs.

So what is the difference between a beetle and a true bug?
Beetles' first pair of wings form a hard shell, they have chewing rather than piercing mouths unlike other insects that resemble beetles, and their larvae generally have an elongated body with three sets of legs at the front and no claspers at the back, with the claspers differentiating them from caterpillars.

TAMU (Texas A&M University) explains:
"Beetles are the most common type of insect. Beetles are everywhere. But beetles can be confused with other kinds of insects, especially some true bugs. So how do you recognize a beetle?

First look for the wings and wing covers. Most insects have wings, and those that do have two pairs. Beetles differ from all other winged insects by having the first pair of wings hardened and thickened. These hard forewings serve as a protective shield for the fragile flying wings, which are folded underneath. In fact the Latin name for this order, Coleoptera, means “folded wing”. Wing covers in beetles meet in a straight line down the middle of the back [the simplest test for a beetle is the one invented by school boys long ago–if it crunches when you step on it, it was probably a beetle (wing covers are brittle)–but let’s not].

There are a few true bugs (Order Hemiptera) whose wings somewhat resemble beetles, but true bug wings are only partly hardened and thickened. The outer half of true bug wings are translucent. The two groups can also be distinguished by their mouth parts. Beetles always have chewing mouth parts, while the mouth parts on true bugs are designed for piercing and sucking. If you flip the insect over, look under its head. If there is a ridge extending from the tip to the end of the head, it’s probably got piercing-sucking mouthparts and is not a beetle.

There’s one other complicating factor in recognizing beetles. Before emerging as winged adults, beetles undergo a very different-looking immature (or larval) stage. The larval life stages of beetles are very diverse in appearance, but generally are elongate with three pairs of jointed legs at the front of the body. They are told apart from caterpillars by the lack of claspers on the hind segments of the body."

Texas A&M is an excellent resource for bug identification, and for reference to domestic and North American birds and mammals. Despite all the Aggie jokes, they really are a top school for veterinary and zoological fields.

So what colors and patterns do ladybugs come in, and more importantly, why do they have these variations in pattern?
Ladybugs can be white, gray, yellow, orange, red, pink, or even black. They can have up to 15 spots or no spots at all. The number of spots helps identify the species, but morphs within the species can cause issues with spot counts. They can also have dim spots, distinct spots, white spots on their heads that help us differentiate the species, and can even have red spots on a black body.

The most compelling hypothesis I have found is this:
It has to do with climate, specifically temperature and solar exposure. The species that survive in an area, and the morphs of those species that best succeed, are determined by the insects' ability to thermoregulate, a process controlled largely via sun exposure and heating of their shells.


The magazine Science gives a rundown of a Cambridge study about climate's effects on ladybug coloration (their study used two spot ladybugs):
"aul Brakefield, an ecological geneticist at the University of Cambridge in the United Kingdom and colleagues have studied the two-spotted ladybugs for decades, intrigued by why different populations of ladybugs have different colors. In 1980, 10% of the ladybugs living near the coast were black with red spots, or melanic, whereas 90% were red with black spots, or nonmelanic. In contrast, 40 kilometers inland, 40% of the ladybugs were melanic and 60% were nonmelanic. The color difference was likely an adaptation that allows the darker melanic ladybugs to stay warm in the cooler inland climes, whereas a lighter color prevents the nonmelanic bugs from getting too hot on the coast. One protein is responsible for the difference between the two colors, and the genetic switch from one to the other is very simple. But the researchers still don't know how exactly sunlight or temperature influence ladybugs' color.

Over 25 years of sampling insects, Brakefield and his colleagues noticed a change. As they continued to catch hundreds of ladybugs every 5 years or so, over 50 generations of ladybugs, they found more of the nonmelanic bugs, even when sampling inland. In 2004, the last year in which the researchers could gather enough ladybugs to see a significant trend, they found that only 20% of the ladybugs in any area were melanic. The trend seemed to fit with temperature data over the period, which showed that the entire area had been consistently warming, the researchers report in the December issue of Heredity."

You can find the December issue of Heredity here. There is no paywall and it is the full study. This is the juicy part:
"The two-spot ladybird shows a number of genetically distinct colour morphs (Majerus, 1994). These morphs can be classified into two discrete classes, namely those that are predominantly black with red spots (melanics), and those that are red with black spots, usually one on each elytron (non-melanics; see Figure 1). A co-allelic series of alleles for melanism are genetically dominant to the recessive non-melanic, or typica, allele. The frequency of these morph classes varies geographically, and numerous examples of clines have been described in different countries (see Majerus, 1994). The geographical variation in morph frequencies in the Netherlands has been partly accounted for in field and laboratory studies by thermal melanism (de Jong et al., 1996). This hypothesis argues that the larger surface area of dorsal, black cuticle in the melanic morphs gives them a thermal advantage relative to non-melanics under conditions where activity is limited by the absorption of solar radiation (see de Jong et al., 1996 and references therein). Based on the results from laboratory experiments measuring the temperature profiles and activity of beetles of each morph under differing conditions of radiation, heating and convective cooling, melanic beetles are expected to have a thermal advantage over non-melanic beetles in the field whenever: (1) ambient temperatures are low; (2) the amount of wind is low; (3) sunshine is intermittent; and/or (4) the radiation intensity is high (de Jong et al., 1996). Thirty years ago, such conditions tended to occur in the east of the Netherlands away from the coast during the spring and early summer when ladybird beetles are emerging from hibernacula to feed on aphids and reproduce. Since that time, the climate inland at this time of the year has tended to become warmer with less cloud cover, and, thus, more similar to that along the coast (see de Jong and Brakefield, 1998)."

Can you tell me more about morphs?
Sure! So a morph is just a horse of a different color, or in this case, a ladybug. It's the same species as its counterparts, but has variances in shell color and spot appearance. It is thought carotinoids give ladybugs their red color, and their shading is a result of different levels of melanin. The cause of the variations is thought to be climate-related.

What about half-and-half colored ladybugs?
Ask Entomologists has as good an explanation as you're going to get (here are excerpts but I suggest clicking the link because it goes in-depth and has videos!):
"We’ve gotten a lot of questions about ladybugs which are half yellow-brown and half red. This isn’t a normal situation by any means, and it only happens in maybe one in every ten-thousand beetles based on what I’ve seen while raising ladybirds. It’s an example of a deformity, and an interesting one at that.

So what’s going on here?

There’s two things which could be happening in these pictures, and I can’t say with certainty which one of the two choices it is. However based on what’s known about ladybug coloration, I believe this is an injury which happened while the beetle was squeezing out of it’s pupa."

"We’re interested in which machines paint the ladybugs. Unfortunately, there’s not a lot that’s known about how beetles paint themselves. Most of the information that’s out there focuses on butterflies. That’s okay, though, because we can describe how butterflies work and make some educated guesses about how this all works in ladybugs."

"Hypothesis 1: The ladybug got hurt while squeezing out of it’s pupa
We can tell a lot about what’s going on by looking at these pictures, and watching a ladybug after it gets out of the pupa."

"When the ladybug gets out of it’s pupa, it’s colors aren’t fully formed. These colors form within a few hours to a few days. First, they’re a spotless pale yellow. Then, their spots develop and the rest of the wings slowly turn orange or red. This is what that process of stuff getting passed around the assembly line looks like from high above, the color of the wings slowly changing.

Ladybug blood is a pale yellow, so the first color you see is likely blood. In butterflies, the precursors get made shortly after the butterfly emerges from the pupa. So if there’s an injury to the wing which blocks the blood supply in this narrow window, the machines won’t get their raw materials. If the machines don’t get the materials they need to make red paint, the wings won’t turn red.

Hypothesis 2: The ladybug is split down the middle.
I believe this one to be less likely for a number of reasons too complicated to fully discuss here, but there’s another possibility: the ladybug is a mix of slightly different machines.

Bugs develop differently than people, but in people there’s a genetic condition called heterochromatism which is a really fancy way of saying that a person has two different eye colors. Actress Mila Kunis has this condition.

The directions for the machines that make the paint in ladybugs are stored in DNA segments called genes. Some machines, like optix, tell the ladybug what to build and where to build it. The ladybug gets two copies of the directions (called alleles), so there’s a backup if one machine’s directions are broken.

Sometimes, while the bug is being built, the directions for both copies of the machines end up being broken. This is called a mutation. If the mutation happens in the right time and the right place, the ladybug won’t look the same on each side.

However, I think this is less likely than the first one I discussed. The reason I think this is less likely is because the eyes of the ladybugs our twitter followers sent us are dark. There are mutations in ladybugs which cause the wings to be yellow. In most, but not all of these mutations, the yellow ladybugs also have white eyes.

The eyes on both of these ladybugs are black, so I believe this to be an injury. However, there’s no way to know without extensive genetic testing…and this is really expensive. Even then, I wouldn’t be able to do it without knowing which genes in the ladybugs make color.

The Bottom Line

The above discussion is largely an educated guess, because there’s not a lot that’s known about how ladybugs make colors. My guess is based on what happens in butterflies, but beetles are really different than butterflies and it’s likely the process is completely different in beetles.

One really important question which needs to be answered about ladybug beetle coloration is what ladybug paint is made of. Butterfly wings are painted red by chemicals called ommachromes, but some researchers believe that ladybug wings are painted red or orange by another group of chemicals called carotenoids. Carotenoids are the chemicals which make carrots orange, and make tree leaves turn red in the fall.

This creates more questions than answers, however. Not a lot of animals produce carotenoids, but ladybugs just so happen to eat aphids…which are one of the few animals which make this kind of paint. Carotenoids aren’t known to darken bug eyes, which doesn’t explain why yellow ladybugs have white eyes."

With approximately 500 species in the US, and 5,000 world-wide, how do ladybugs tell eachother apart to mate? Can and do different species hybridize?
Each species has different pheromones that allow them to identify eachother. I can currently find no information about hybrids or if they are capable of hybridizing.

An explanation of ladybug mating:

"Each species of ladybug has its own pheromones for attracting a mate. When they find each other, the male grips the female from behind and holds on tight. They can copulate (stay together) for more than 2 hours at a time. Female ladybugs can store a male's sperm for 2-3 months before laying eggs. Ladybugs tend to lay their eggs where food is abundant."

How do I identify my local ladybugs?
If you are in the US, the most common is the five spot, if you are in Europe, it is the seven spot, but in both places the Asian ladybug exists. There are identification guides. You will need to look at the color of the head, whether it has a white spot, the color of the beetle, the number of spots, and the body shape. Because of the morphs, the body shape and particulars of the head are the most defining traits to help you identify your ladybug.

Try this Ladybug Identification Guide. It uses pictures and process of elimination so it's a good place to start if you really must know what that bright, shiny thing is.

Is that thing about ladybugs being named for Our Lady the Virgin Mary true?
Probably. Helen E. Roy's "Ladybirds" perpetuates this idea, and Bishop Barnaby in "Notes and Queries", but I have not found a definitive source or date for this notion. Etymology Online says the term dates back to 1670. One Catholic source says this name was the result of an aphid infestation stopped by ladybugs in the middle ages; the story either goes that people prayed to Mary and the beetles killed the aphids, or that the beetles got the name Our Lady's Bug/Ladybird/Ladybug because of the Virgin Mary's association with a red robe, and the European beetle having seven spots. While Christians often turn things retroactively into Christian symbols, this naming convention likely is theirs even if the reason why it happened isn't clear.