Who would think that insect larvae can
be interesting? They don't have much to offer when compared to their
adult counterparts. We can't help but notice adult insects. They fly,
they buzz; in fact they can make quite a racket during hot summer
nights. Some blink their little green lights over the meadows. Others
wear flamboyant colors that seem like works of art.
Larvae, on the other hand, at least
most of them, lead obscure, secluded lives, hiding in secret places.
They are rather colorless and shapeless worm-like things, with stubby
little legs or no legs at all, with tiny eyes or no eyes at all. None
of this is surprising. Larvae have only one function in life, eating
and growing bigger. They have nothing to do with the more exciting
things like sex. That is left for the adults. Well, larvae actually
have two functions. They possess strategies for fighting or evading
enemies. Despite such dull lives some insect larvae manage to be
quite interesting.
Lightning bug larvae have green lights
along their bodies. They look like little trains, and that is what we
call them in Argentina, trencitos. One wonders about the purpose of
these lights. Adults use theirs to attract members of the opposite
sex, but larvae have nothing to do with that. These lights must serve
another purpose. It turns out that lightning bugs are highly toxic and
bad tasting, so the lights are telling predators to stay away and avoid the unpleasantness.
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Monarch caterpillar
© Beatriz
Moisset
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Some caterpillars use the same
strategy. The monarch butterfly caterpillar wears bright black, yellow and white colors arranged in a bold
pattern to advertise its toxicity obtained from feeding on milkweeds. Other caterpillars have a variant of this method. The
eastern swallowtail butterfly is large and colorful with a pattern of
black and yellow. The larvae change their appearance dramatically as
they age. The nearly fully grown caterpillar is bright greenish
yellow with
two large eyes on its head,
except that these are not real eyes but just look like them. It is
thought that this feature serves to deter predators that erroneously
assume that they are dealing with a larger and more powerful creature
at the sight of these large eyes. They have another feature for
defense against enemies. When threatened, they pop up two bright
antenna-like threads. These appendages emit a nasty smell that seems
to be effective in keeping other creatures away.
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Eastern
swallowtail butterfly caterpillar.
Showing its
osmateria when threatened
©
Beatriz Moisset
|
Some larvae feed on extremely poor
food, such as leaves or wood. It is rather remarkable that they
manage to extract nutrients out of them, especially the ones that
feed on wood. Most of what they eat goes through their digestive
system and comes out of the other end with little modification. A
partially rotten log may contain long tunnels filled with what looks
like sawdust. They are the holes made by beetle larvae as they grow
and advance in search of more food. The sawdust is their poop, which
takes the name of frass. Some caterpillars live inside a bunch of
leaves which they tie together and curl up so they can hide from
predators while they munch away. If you open one of these bundles you
find a large amount of frass surrounding the caterpillar.
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Caterpillar
and some of its refuse
or frass
©
Beatriz Moisset
|
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Larval
tunnels on wood (possibly
a beetle)
filled
with frass
©
Beatriz Moisset
|
At the other end of the spectrum, there
are larvae whose mothers have provided with a rich, highly nutritious food.
Many wasps and bees do that. In the case of wasps, the food is
insects or spiders; bees, on the other hand, collect pollen and
nectar for their brood. These larvae live in splendid isolation
inside small compartments, called cells, built by their mothers. The
amount of food supplied is slightly larger than the future adult bee
or wasp. Almost all of it is converted into flesh and nothing is
wasted. At the end of the larval stage, only a
small pellet of fecal matter is produced. It gets the name of
meconium, comparable to the first bowel movement of a newborn baby.
The baby's meconium is the accumulated waste of a few months; so the
similarity is strong.
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Cell of
Crabronid wasp larva (Trypoxylon
collinum)
Opened cell
reveals the fully grown larva and the pellet of meconium (left)
No remains of
the spiders that fed this larva
©
Beatriz Moisset
|
A lot more can be said about larval
poop. A number of larvae use their own fecal matter to keep enemies
away. Some carry their own feces as an umbrella, others build a
little case. They hide inside it the way a snail hides inside its shell.
Some insect larvae don't use real poop, but it looks like it. A
whole group of caterpillars is called bird-dropping caterpillars.
Still others fling their waste as far away as possible so as not to
give away their position to possible enemies. I don't need to repeat
these stories as I have written about them in two articles that you
may find interesting:
"The Poop Bug and the Golden Beetle,"
2009 and
"Poop Flinging and Other Poop Strategies," 2012.
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Golden tortoise beetle
larva carrying its feces
©
Beatriz Moisset
|
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Neochlamisus beetle larva and its fecal case
©
Beatriz Moisset
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List of articles
Beginners
Guide to Pollinators and Other Flower Visitors
© Beatriz Moisset. 2017
