Larval Animal Life Cycles

By Evan Sandsmark - November 29, 2012 227 recent views

After answering scores of questions from readers, one thing has become clear: people often mistake various types of larvae for worms. In fact, we probably write more about larvae than we do about worms, which is not entirely surprising, considering that the larvae of many types of creatures (beetles, flies, butterflies, moths, etc.) are very common. Because there is evidently such great interest in the larval form of certain types of animals, we figured we should write an article about larval animals and their life cycles, with a particular focus on the creatures whose larval forms are most commonly mistaken as worms.

First, we should state that it is somewhat misleading to say that various types of larvae (say, caterpillars and maggots) aren’t worms, as there really isn’t such thing as a worm, at least if we are to speak with perfect scientific precision. The word “worm” refers to an obsolete taxon – it is a relic from an age when taxonomy wasn’t nearly as complicated or well-delineated as it is today (although things are far from settled even now). Be that as it may, there is obviously an everyday sense of the word “worm,” one that is used to refer to creatures like annelids (like earthworms) and nematodes (various types of flatworms), and it is this usage that we adopt on this site. A creature like an earthworm, however, is quite distinct from something like a caterpillar, which merely passes through a “worm phase” before becoming a butterfly or moth. So, although there is no good scientific reason to say that a maggot or caterpillar isn’t a worm (because, again, nothing is technically a worm), you can see why it makes a certain amount of sense to keep animals that merely pass through a larval stage separate from animals that do not. In short, larval animals are only temporarily worms, whereas worms are always worms, generally speaking.

While there are a wide variety of larval animals (ranging from mosquitoes to fish to amphibians), only a few are commonly mistaken as worms during their larval stage: flies, beetles, and butterflies/moths, the larvae of which are known as maggots, grubs, and caterpillars, respectively. (“Grubs” can also refer to the larval form of bees and wasps, which are worm-like at this stage in life, but for whatever reason we’ve never received a question about bee or wasp larvae, so we’ll pass over them.) All of these creatures broadly go through the same life cycle: they begin as eggs, transform into larvae, pupate, and then emerge from this development as adults.

The cycle begins when adults lay eggs, often in great quantities. (Some beetles, for instance, lay thousands of them.) These eggs are deposited near a food source that the larvae can consume. Larvae are almost always extraordinary eaters, spending their window of existence consuming any food they come in contact with to drive their future development (i.e., the pupate). The pupa stage of the life cycle involves the organism’s transformation into an adult form; it is when the “worm” becomes a beetle, fly, or butterfly. This transformation can in many cases be quite dramatic, as when a caterpillar morphs into a butterfly. Once adults, these creatures reproduce, leading to a new set of eggs to begin the process anew.

Of course, there is great diversity within this framework of development. For instance, the stages of the life cycle can last vastly different lengths, and only in some species of beetle and fly do the pupa cocoon (a la butterflies and moths). However, overall, they follow a similar life cycle, with the different stages of development corresponding to similar biological ends (e.g., larvae tend to consume lots of food, as mentioned above, to drive their development into adults).

With a bit of luck, we have helped clarify the difference between worms and larval animals, and in so doing provided some helpful information about both creatures. To do so, it was necessary to dwell on the life cycle of larval animals, as it is only in the context of this life cycle that one can make sense of the larval stage of development. Hopefully it will now be easier for readers to distinguish between larvae and worms while simultaneously recognizing that the latter don’t even exist, properly speaking.

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