Beneficial insects Harmful insects

Understanding Insect Life Part 1: From Egg to Larva

If I’m talking about voracious babies and adults prettier than the young, I’m obviously not talking about me, but about insects! I want to set the record straight about the life cycle of these little creatures. I’m not going to tell you how to get rid of or attract X insect (there are already several articles on the subject), but rather I want to tell you how to understand these animals.

With this point alone, I’m sure many people have said to themselves: “Oh, yeah? Aren’t insects just… bugs?” Well, no! They’re really part of the animal kingdom!

Photo: Pixabay

Why Talk About the Life Cycle?

Because by better understanding your six-legged enemies or friends, you’ll better understand what’s going on in your home, your plants, your garden and maybe even your lawn! Because you’ll be able to point the finger at the right culprits, attract your true friends and take action only when necessary.

And because it’ll help you recognize them, plain and simple!

“Well, Audrey… A butterfly’s a butterfly, you don’t need to know its little name to know that it’s beautiful and that it’s a pollinator!”

Hum hum… You know those beautiful little yellow or white butterflies that fly about a metre above the ground? You see them everywhere in summer. Well, they’re pieridae. Does that ring a bell? Or how about: those pesky green caterpillars that eat all (my!) cabbages?

Photo: kcollin

Ahhhh, I just caught your attention? So, do we like these beautiful butterflies or not? It gets more complicated, doesn’t it?

Understanding the life cycle of insects answers many questions. Can we attract only the adult? Can we rely on the adult’s appearance to recognize the young? When should you intervene to avoid a problem?

But some questions will remain eternally unanswered… Like did Mother Nature know when she created the pieridae that I’d give up growing Brussels sprouts in my garden?

Who knows?

Photo: jessieleah

The Insect Life Cycle: Very Simple!

I’d like to take a few seconds to warn readers who are familiar with the subject, as well as those who like to “scratch around” for points to contradict: this article is a GENERALIZATION that concerns insects with complete metamorphosis. It’s an INITIATION into their life cycle. It’s for a VULGARIZED blog that’s ACCESSIBLE TO EVERYONE.

If you think I’m staying on the surface of my subject… I agree with you! If my comments offend you… Well, have a nice day anyway!

Most insects have a four-stage life cycle: egg, larva, nymph, adult.

That’s all there is to it. It’s as simple as that. Some insects have special names for certain stages: for example, the caterpillar is none other than the butterfly larva. Another name is “pupa” for a fly nymph, or “chrysalis” for a butterfly. But whatever the name given to each stage, the role remains the same.

Let’s take a closer look at each of these stages.

Eggs

I’ve never tried making myself an insect egg omelette, but basically, it’s the same thing as bird eggs. Even if the shape, color and size differ, there are always at least three components in the egg that remain the same, regardless of whether it’s a fish or an aphid. There’s a baby (you’re surprised, I know!), a food supply and a protective liquid of varying thickness.

(I’m having a really hard time finding good pictures for this article. Here’s the least confusing, clearest, simplest, unidentified English image of the inside of an egg I could find… As nothing is perfect, there’s no baby in the coconut!)

Unfortunately I didn’t receive a single chocolate egg for indirectly advertising this joke, and I’m very sad about that… But if Cadbury reads this and wants to send me a case, email me for my postal address!

Let’s move on:

The more perceptive have guessed it, I’m talking about the yolk and white of our chicken eggs. You don’t have a chick in the eggs in your fridge, but the other two components are there: the yolk is the equivalent of the placenta (or the lunchbox) and contains fats and nutrients. The white is like an inflatable cushion (or Jell-O) that prevents the baby (or its lunch) from bumping into the shell.

For insects, it’s the same: a lunch box and protective Jell-O, which can be any color, by the way. Don’t ask me for a picture of the inside of an insect egg; I’ve searched for at least 1 hour for a chicken egg, without success, so…!

Photo: Macro Photography 

Larvae, Caterpillars, Worms and So On

Since larvae don’t fly, they’re rarely seen. They live in the leaves, in the wood, under the earth – in short, not in your glass of wine when you’re out on the terrace. But even if you don’t see them, they’re very present, even more so than the adults that get up your nose when you’re riding your bike!

These larvae are of vital importance to the food chain. Birds, reptiles, mammals, insects and invertebrates feast on them. That’s why insects lay huge numbers of eggs. Depending on the species, only 5% or 10% of the eggs laid may become adults, or even less!

Photo: Tina Nord

Imagine that one year, for whatever reason, you decide to put spider repellent on your patio tiles. A month later, you write to me in a panic: “I don’t know what’s going on, I’m invaded by flies this year!”

…Well, yes, the predation rate of larvae on the ground may have dropped by half: that’s normal!

Don’t underestimate the number of invisible baby insects under your nose.

Apart from the fact that larvae exist to be eaten, there’s another very important point to mention about them: their one and only purpose in life is to eat, eat, eat and eat some more! (Just like me…!)

Eat or Be Eaten: Such Is the Life of Larvae!

For the Laidback gardener, this is both a blessing and a curse. Some larvae are pest predators: we love them.

Ladybug larva. Photo: trilliumjames
Lacewing larva. Photo: muecke2000

Other larvae are decomposers, recycling organic matter. We love these too!

Maggots, fly larvae (not too cute, I know!). Photo: Wikipedia

But then come the herbivorous larvae… And that’s when things go wrong at the shop, as my grandfather would say.

Butterfly larva. Photo: Pamela Marie
Crane fly larva. Photo: Simon / flickr.com

Larvae eat a lot, as the transformation into an adult requires a lot of energy, and they need to get there quickly to remain prey for as short a time as possible. Depending on the species, some eat several times their weight every day.

In the case of herbivores, such as caterpillars, which are the most harmful to gardeners, they generally remain on the plant where they hatched. Fortunately, they’re not the most mobile (compared to predatory larvae, for example), which is why a simple floating cover over plants is often enough to protect against herbivorous larvae: if the adults can’t lay eggs there, the larvae simply won’t find your plants!

In the case of larvae that live in the soil and eat the lawn from underneath, such as crane fly larvae, there’s no such easy solution… Try planting something other than grass: clover, dandelion, plantain and other “weeds” are not edible for these grass-loving pests.

Cocon: la transformation extrême!

In fact, I’ve given you a lot of material already, and since the article is so long, we’ve decided to… cut it in half!

So I’ll leave you to ponder your new knowledge and stew until next week to complete the information on the insect life cycle.

Tourelou!

Audrey Martel is a biologist who graduated from the University of Montreal. After more than ten years in the field of scientific animation, notably for Parks Canada and the Granby Zoo, she joined Nature Conservancy of Canada to take up new challenges in scientific writing. She then moved into marketing and joined Leo Studio. Full of life and always up for a giggle, or the discovery of a new edible plant, she never abandoned her love for nature and writes articles for both Nature sauvage and the Laidback Gardener.

2 comments on “Understanding Insect Life Part 1: From Egg to Larva

  1. Patricia Vollstaedt

    I always enjoy your articles, especially the humorous bent you use to convey a lot of useful information. I grow only flowers now, with a couple of pots of tomatoes and herbs scattered here and there amongst the perennials. My question concerns those little cabbage butterflies: I love them flitting around and would like to grow ornamental kale, or cabbage, to encourage them to lay eggs here. I don’t have to worry about vegetables getting eaten, and I figure the caterpillars will be a great food source for birds. Will these ornamental plants attract the butterflies like the real deal? If not, can you suggest what I might grow that does not require a huge amount of space? Thank you,

    • Mathieu Hodgson

      They will atrract cabbage butterflies as any member of the brassica genus.

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