People love ladybugs. And what's not to love? They're cute as a button with their teeny hard, red shells with black spots. It's even considered good luck if one lands on your hand or you see one in your home. Plus, they're completely harmless to humans. Farmers love ladybugs because they enjoy feasting on plant-eating insects like aphids, according to National Geographic.

But ladybugs are disappearing across the United States, and scientists don't know why. One theory is that non-native species, such as the seven-spotted ladybug from Europe (Coccinella septempunctata) and the Asian ladybug (Harmonia axyridis), have proliferated so successfully here that native ladybugs have been pushed out of sight. Another theory says those non-native species are due for a decline themselves, so the disappearance may just be part of a natural cycle.

Here are five little-known facts about these popular garden predators.

1. Technically, they're lady beetles, not bugs. What's the difference? For starters, bugs have needle-like mouth parts whereas beetles have chewing mouth parts, according to the Australian Museum. Plus, beetles have harder wings than bugs do (if they have them at all). Also, bugs have a mostly liquid diet and beetles don't.

In Europe, they're called ladybird beetles.

Yellow ladybug Ladybug spots — which some species don't have at all — sometimes look more like stripes. (Photo: tcareob72/Shutterstock)

2. They aren't all red with black spots. Though that may be the most common way to imagine a ladybug, it's not what all species of ladybugs look like. There are about 5,000 species of ladybugs in the world, National Geographic reports, including 500 in the United States. They also can be yellow, orange, brown, pink or even all black, and their spots — which some ladybugs don't have at all — can look more like stripes, as the above photo shows.

Ladybug eating aphids A ladybug doing its job: eating aphids. (Photo: Henrik Larsson/Shutterstock)

3. A ladybug may consume 5,000 aphids in its life. In fact, as soon as ladybugs hatch, they begin to feast. Ladybugs lay eggs — hundreds of them — in aphid colonies, and when they hatch, the larvae immediately start feeding. "Once hatched, the larvae eat about 350 to 400 aphids in the two weeks it takes them to become fully grown," the San Diego Zoo says.

But they don't just eat aphids — they also eat fruit flies, thrips, mites and other plant-damaging insects.

However, different species prefer different foods. While many prey on garden pests, some (like the Mexican bean beetle and the squash beetle) also feed on the plant leaves mentioned in their names, making those particular species unwelcome guests in some gardens.

Ladybug on flower A ladybug's spots are a warning to attackers: You really don't want to eat me. (Photo: Darkdiamond67/Shutterstock)

4. A ladybug's spots warn potential predators. The spots and bright colors are meant to warn would-be attackers that this beetle tastes terrible. "Ladybugs can secrete a fluid from joints in their legs which gives them a foul taste," National Geographic reports. (If you've ever heard that ladybugs can have stinky feet, this is why.) They've also been known to play dead, giving them a two-pronged defense system in a world of eat or be eaten.

Because of this, they aren't often preyed upon, however several insects, such as assassin bugs, stink bugs and spiders, may eat ladybugs, according to the Lost Ladybug Project.

5. The "lady" part of their name is said to refer to the Virgin Mary. No, "lady" does not mean all of the bugs are female. Here's the backstory, courtesy of the Lost Ladybug Project: "During the Middle Ages in Europe, swarms of aphids were destroying crops. The farmers prayed to the Virgin Mary for help — and help came in the form of ladybugs that devoured the plant‐destroying pests and saved the crops. The grateful farmers named these insects 'Our Lady’s beetles,' a name which had endured to present day."

Angela Nelson ( @bostonangela ) is an exhausted mom of two young daughters and two old cats, and a Pulitzer Prize-winning digital editor with more than 15 years of experience delivering news and information to audiences worldwide.