Top 10 Bizarre Larvae


Most of you probably know that caterpillars turn into butterflies, and maggots into houseflies; both examples of an animal transforming from a “larval” to “adult” stage. Besides these famous insects, however, are thousands of other species who undergo bizarre and extreme transformations during their life cycle. Larval stages are especially extreme in creatures of the sea, and sea life will be constituting almost all of this list.

10. Tortoise Beetles

golden tortise beetle larvae by Larah McElroy

golden tortise beetle larvae by Larah McElroy

The only land animal I’ve decided to include, larval tortoise beetles are hairy, spiny little grubs who protect themselves under a large clump of their own dried-up feces, collecting all of their poo into a foul, but sturdy shield throughout their childhood. When they metamorphose into adults, however, these “ugly ducklings” of the beetle world will become cute, ladybug-like insects with a variety of beautiful color schemes, sometimes even shining gold. While lots of insects have some pretty weird larval stages, the rest of our entries are going to be sea-creatures; they just tend to go through even more extreme transformations.

Tortise Beetle Adult by Grant and Caroline

9. Mola Mola

Mola Mola

The ocean sunfish or “Mola mola” is sometimes called a headfish, since it bizarelly resembles a fish head with no body. Living on a diet of only jellyfish, Mola mola can grow to over a ton and are among the largest bony fish in the world, but begin their lives as round, spiny creatures smaller than the period at the end of this sentence. We don’t know exactly how long it takes these prickly pipsqueaks to mature, but it’s likely a lot faster than you think; one young Mola at the Monterey Bay Aquarium gained over 800 pounds in little over a single year.

8. Flounder


An unusual case of a very normal-looking fish becoming a heck of a lot stranger as it grows up, a flounder begins its life as a fairly conventional fish-fry, but as its gets older, it begins to lean more and more to one side, and one of its eyes will actually begin to migrate around its head. As an adult, this camouflaged carnivore lies completely on its side, with both eyeballs on the opposite side of its skull to stare upwards at prey.

7. Barnacles


Barnacles seem to develop on almost any sturdy object regularly exposed to seawater, but few people realize that these tough little lumps are actually “bugs,” or to be exact, Crustaceans like crabs and lobsters. Their one-eyed, swimming larvae are similar to the larvae of fellow crustaceans, but will eventually cement themselves upside-down to a hard surface for the rest of their lives, forming a hard shell and kicking their hairy legs to trap plankton and other food particles. Certain parasitic species get even stranger, losing most of their bodies as they mature and growing into root-like filaments throughout the bodies of their host animals.

6. Sea Squirts

Larval tunicates

Larval tunicates or “sea squirts” closely resemble tadpoles and are actually related to us vertebrates. They share much of the same anatomy you and I had in our earliest embryonic stages, including the “notochord” that became our spines. Many tunicates, however, will lose their notochord and even most of their brains when they settle down as adults; like barnacles, they will attach head-first to a hard surface and become a filter feeder. Hollow and bag-like, the adult sucks seawater into a lower “mouth” cavity and squirts out through an upper “anal” cavity.

5. Viperfish


In the perpetually dark, pitch black deep-sea abyss, Viperfish, also called Dragonfish, are among the top predators. As larvae they are threadlike, frail creatures with tiny, tubular mouths, and most unusually, eyeballs that dangle behind them on long stalks. As they mature into long-fanged hunters, their eyestalks will slowly “reel in,” and can still be found coiled inside the adult skull.

4. Parasitic Snails

Enteroxenos oestergreni

Enteroxenos oestergreni is a type of sea snail and begins its life as a swimming larva just like those of other sea snails, including a tiny, coiled shell. Eventually, however, it will enter the body of a sea cucumber (an animal related to starfish) and lose everything resembling snail-like anatomy. The adult is a parasite closely resembling a tapeworm, its body a repetitive chain of reproductive organs and eggs.

3. Tapetails


One of the oddest larval legends, the aptly named “tapetail” is a transparent, almost jellylike fish which undergoes a very different transformation depending on its sex. Descending into the deep sea abyss as they mature, female tapetails mature into “whalefish,” hungry predators named for their immense mouths – some of them even sporting tooth-lined gills which function as additional mouth openings. Males, conversely, become “bignoses,” who never even eat at all in their short life of mating. Remarkably, these three forms are so drastically different inside and out that for centuries, we believed they were completely different families. Though we only ever found female whalefish and male bignoses, it took until the 2000’s to figure out that both began life as tapetails and were sexes of the same animal.

2. “Pig Butt” Worms

Pig Butt Worm by Karen Osborn

Yet another inhabitant of the deep-sea abyss, the “Flying Pig Butt” is actually an annelid, like earthworms and leeches, but its segments form a more ball-like than worm-like shape. Floating in the open water, the pig butt dangles a net of mucus to trap tiny particles of food and slurps it back up, which is just the perfect way for a butt-shaped worm to eat, isn’t it? While already bizarre enough, the weirdest thing about the Pig Butt is that absolutely none of them have been found with reproductive organs, implying that these creatures are, in fact, in a larval state. They bear some similarities to the (less butt-shaped) larvae of certain tube worms, but the marble-sized pig butts are nearly ten times the size of these other larvae. Do you even WANT to know what a mucus-spitting butt worm turns into? Of course you do, don’t lie. Until it’s figured out, I’m just going to call the mystery sea-beast Butthulhu. You call it whatever you like.

1. Symbion Pandora

Symbion Pandora

Found living only on the mouthparts of lobsters, these tiny animals belong to their own unique phylum (to get an idea of how major this is, all animals with internal skeletons – fish, reptiles, birds, mammals and amphibians – are a single phylum, the Chordata) and use their fuzzy wheel-like mouths to vacuum food particles from the water. Their life cycle is one of the most complex and unusual in the animal kingdom, and you’ll be forgiven if you get a little lost here:

Symbion spend much of their existence in an asexual feeding stage, permanently attached to their lobster where they vacuum food particles out of the water. Neither male nor female, feeding stages reproduce by cloning themselves until they thickly line the lobster’s mouth. When the lobster they live on is about to molt (discarding its old shell, and all the symbion with it!) some symbion grow a female inside their body, while others grow what has been named a “Prometheus larva.” The Prometheus larva does not transform into the male, but “gives birth” to two or even three males at once, who have massive reproductive organs but no mouths or digestive tracts. The swimming males attach themselves to any females they can find, and once impregnated, a female crawls away from the feeding stage body. Finding an empty spot on the lobster, she transforms into a hard, egg-like cyst, and a special, torpedo-like “Chordoid larva” larval will eventually hatch out of her. This fast, strong swimmer exists only to quickly find another lobster, and there it will transform into a new feeding stage…cloning itself until the process must begin again.

By Jonathan Wocjik at

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  1. I don’t think the writer understands what a larvae is. Fish cannot be included as they don’t have a larval stage by any sort of scientific classification or definition. Please fact check before posting a headline!!!! Should of been called top 10 animal transformations or metamorphosis’.

  2. Very Good and informative list, however it would have been good to have before and after pictures like no. 10 =)