Reputation: Ladybirds are pretty little beetles, adored by children for their black-on-red spottiness and friendly crawling-over-hand behaviour. Gardeners love them because they eat all those nasty aphids.

Reality: True, true. But there's more to ladybirds than this. Most are highly promiscuous. Sexually transmitted diseases are common. Many species show cannibalistic tendencies.

Are they called ladybirds or ladybugs? Whichever you prefer, the Coccinellidae (as scientists call them) are not quite what they seem.

For starters, many of the 5000-odd species look nothing like the bright and pretty stereotype forged during childhood (tweet this). There are 47 species in Britain, but only 26 have a classically ladybird-like appearance, says Helen Roy of the Centre for Ecology and Hydrology in Wallingford, UK, and head of the long-running UK Ladybird Survey.

The number of spots has nothing to do with the ladybird's age

So what makes a ladybird a ladybird? It's nothing to do with spots. They usually have 11 segments in their antennae, and four components that make up their toes – although the third is small and almost hidden in a groove in the second.

Nevertheless, many ladybird species do have wonderful colours, and lots have spots. The patterns appear on their hardened, protective forewings, which are known as "elytra".

However, the number of spots has nothing to do with the ladybird's age, as many children continue to believe well into adulthood. In temperate zones, most ladybirds live for around a year.

Coccinellidae also eat a broad range of diets. The 24-spot ladybird eats plants. Some species have a penchant for fungus, like the mildew-munching orange ladybird. Others target limpet-like scale insects. But the gardeners' favourites are those that prey on aphids.

These ladybirds lay their eggs on leaves close to an aphid colony, but they have to be smart about it. Aphids are parthenogenetic, capable of birthing clones without the hassle of sex. This means that an aphid colony can grow extremely fast and may suddenly crash, with a few winged aphids flying off to pastures new.

To be sure that her larvae will enjoy a plentiful diet of aphids, a female ladybird must lay her eggs when the aphid colony is in its early stages. She achieves this by assessing several cues, including the density of the aphids, the honeydew the aphids produce, and the volatile chemicals released by an aphid-infested plant.

Ladybird larvae are eager cannibals

"They can also pick up one another's footprint chemicals," says Roy.

There are at least 40 different components – mostly alkanes – that larvae leave in their tracks. If a female ladybird gets a whiff of them, she'll usually go somewhere else to lay her eggs.

This is a sensible precaution, because ladybird larvae are eager cannibals.

Roy and her colleagues have shown that 2-spot larvae that manage to gobble up one of their yet-to-hatch siblings will develop much faster and are much more likely to survive to adulthood than larvae deprived of the opportunity to be cannibals (tweet this). So if an aphid colony already has ladybird larvae, a female will do well to avoid it.

Ladybirds don't have as much control over aphid numbers as gardeners like to imagine

Assuming that a female ladybird can locate a suitable aphid colony, her offspring are likely to thrive. "When they emerge from their eggs they are so tiny," says Roy. "They look like they are having a piggyback on their aphid prey when they manage to successfully get hold of one."

That said, several studies show that the aphid-eating ladybirds don't have as much control over aphid numbers as gardeners like to imagine.

In case you are still blinkered by an unqualified love of the Coccinellidae, there are a couple of other truths about ladybirds that you ought to be aware of.

First, they are highly promiscuous. For instance, a genetic study of 2-spot ladybirds revealed that clutches often contain eggs fertilised by three different males, and sometimes more.

A male ladybird passed over his sperm and received 81 larval mites in exchange

Second, STDs are common. Several species, including the 2-spot, are affected by mites called Coccipolipus hippodamiae (tweet this). These parasites live beneath the elytra, where they feed on the ladybird's haemolymph – its "blood" – and have babies.

When ladybirds have sex, it's the mites' chance to move house. In one particularly infectious experimental mating, an unsuspecting male ladybird happily passed over his sperm and received 81 larval mites in exchange.

These sexually-transmitted arachnids can be costly, particularly for females. Compared to uninfected controls, a mite-infested ladybird will typically lay smaller clutches and her eggs will be less viable.

So now you know. Next time your child bends down to cup up a ladybird, you can tell her all about the beetle's cannibalistic tendencies and unseemly sexual behaviour. Or not.