Showing posts with label fecal shield. Show all posts
Showing posts with label fecal shield. Show all posts

Monday, February 06, 2017

Funny Larvae

Firefly larva © Corey Kallstrom
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.

Glowworm (Phengodes sp.) © Ashley Bradford
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.

Monarch caterpillar
© Beatriz Moisset
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.

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.

Caterpillar and some of its refuse or frass
© Beatriz Moisset

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.

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.

Golden tortoise beetle larva carrying its feces
© Beatriz Moisset

Neochlamisus beetle larva and its fecal case
© Beatriz Moisset


List of articles
Beginners Guide to Pollinators and Other Flower Visitors

© Beatriz Moisset. 2017


Tuesday, May 08, 2012

Poop Flinging and Other Poop Strategies



Caterpillar shelter
Many insects eat rather non nutritious plant parts. So they need to consume large amounts, extract the nourishment, such as proteins, and discard the rest at the other end. In simpler words: they eat a lot and poop a lot, or if you prefer, they produce large amounts of frass or waste material.
Wasps are some of the worst enemies of caterpillars. They are constantly seeking them to feed their young. Many wasps are superb at controlling insect pests. I would think twice before hurting one of them; they are our friends. Without them, there would be population explosions of plant-eating caterpillars.

Leaf-roller caterpillar and its frass
Caterpillars have devised different ways to hide and keep these ferocious predators from finding them. The so-called leaf-rollers fold a leaf, stitch it together with their silk and stay inside the little tunnel munching away in relative safety. The amount of frass that accumulates inside these little shelters can be impressive. One wonders how they can live in such conditions. Not pretty!


Tiny black dots of frass hurled by caterpillar
Unfortunately for the caterpillar, the smell of their poop is an excellent clue to their presence. You may say that predatory and parasitic wasps have a nose for food-related aromas. So, certain caterpillars have developed a singular strategy. They throw their waste material as far as they can; which can be pretty far. Eight to twelve inches for a caterpillar not much bigger than a grain of rice! That is as if you could throw the you-know-what several yards away.

The curious thing is that many moths and butterflies belonging to different families have come up with the same poop-flinging solution to hide from predators. Among them there is a skipper that you may probably have seen visiting flowers, the silver spotted skipper. It gets its name from the brilliant spot on its hind wings. When this skipper was a caterpillar it regularly shot cannon balls of its own frass as far as a couple of yards away. How about that!
Silver-spotted skipper



Orchard Swallowtail caterpillar 3148
Bird-dropping caterpillar
(by Malcom NQ, Flickr)
Another poop strategy of sorts is that used by many caterpillars called bird-dropping caterpillars. Their appearance, as the name tells you, resembles a bird dropping. Apparently the ruse is convincing enough to discourage would be predators. No real poop is involved here, but it is worth mentioning in an article about poop strategies.


Leaf beetle larva hiding under its poop
And then, there are other insects, particularly a group of leaf beetles that have turned things around completely. Instead of leaving their poop behind, they proudly carry it around as a shield. Some build a sort of basket or nest above and around them. Others have a projection shaped like a coat rack, from which they hang their byproducts, castoff skin and poop. You can read more about one of them in The Poop Bug and the Golden Beetle

More on frass strategies
 
List of articles 

© Beatriz Moisset. 2012

Tuesday, August 25, 2009

The Poop Bug and the Golden Beetle

Somewhere out there, there is an ugly little bug with a sweet tooth for sweet potato leaves. It goes about munching leaves day after day and growing very fast. It starts life the size of the period at the end of this sentence or smaller and when it is fully grown it is still no bigger than a shirt button. Moreover if you saw one you would think that you were watching a bit of dark poop on a leaf. You would be very surprised when this black you know what started walking around and, if you watched very closely you would realize that there is something alive underneath.

The bug under that nasty dark pile has a funny looking tail with branches and hooks. It looks like a coat rack and the bug uses it precisely for that purpose. When he keeps growing, his skin becomes too tight for him so he grows a new, thin, elastic skin under it and peels off the old one; the new skin has room for growth because it can stretch before it gets harder and it allows room for growth. Each time that the poop bug sheds its old skin, it hangs it on the coat rack. Then the bug adds its own wastes on top of the wrinkled old skin. To do this it sticks out a long and flexible hose coming out from its back end and skillfully spreads the material on top of the existing messy thing. When it dries up it turns dark and rather disgusting. You can see it doing this in this video.

This ill mannered creature carries the whole thing over its body like an umbrella; that is why you can hardly see the bug. Why would it have such a filthy habit? Didn’t its mother teach it any better? Well, it turns out that it has a very clever reason for doing such a singular thing. The poop bug is a tasty morsel that any passing bird would gobble up with relish. But birds don’t feel tempted by this ugly sight, so they fail to see the snack underneath. That is how the little bug can go on munching away unmolested hiding from its enemies in plain sight.

Sweet potato plants look similar to morning glories with climbing vines, light green leaves and pretty trumpet shaped flowers. They look alike for a good reason; they are related. The poop bug likes morning glories just as well as it likes sweet potatoes; so if there are some morning glories in your neighborhood you may be lucky enough to find a poop bug if you look for them. Look at the leaves and if you see holes here and there you may be on the right track for finding a poop bug. Remember that they are very little, no bigger than a shirt button. Also, it may have already left the plant and moved on somewhere else. However, if you see one it is possible that it will wave its umbrella once or twice if startled, hoping to scare away the observer.

After it has been eating almost non-stop for a couple of weeks it will reach its full size and now it will be ready to turn into its adult shape as a beetle, that looks vaguely like a tiny ladybug. This is not an easy transformation; a lot has to take place to make all the changes, grow legs, antennae, wings. So it needs peace and quiet while doing all this remodeling. It may move to another plant nearby, not necessarily a morning glory, sweet potato or related plant, but something altogether different such as goldenrod.

It prefers to anchor itself on the underside of a leaf and once there it sheds its skin one more time and may or may not drop the umbrella along with it. Now it looks like an armored little tank called a pupa. The pupa goes to sleep for just about a week, after which time it wakes up ready to start a new life. During this time not much happens on the outside, but huge changes are taking place inside.

When it is time to come out of this shell the poop grub has one final trick up its sleeve. The front part of the pupal case opens up on two hinges; all what it takes is a little push and the front opens like a double door and the brand new beetle emerges like a car getting out of a garage, a very tight parking space if I may say so.

The gorgeous little creature that emerges bears no resemblance to the larva or the pupa. It is like a tiny turtle; its shell is glossy pink with a hint of gold. And then, depending on how the light hits it, it looks gold with a hint of pink; it may remind you of nail polish. It is pale at first, becoming a little richer and darker in a few hours. It usually sports six black dots; its edge is flared and transparent. The freshly emerged new beetle waves two delicate antennae exploring the new world. It may take a while before it tries its new wings and take to the air. Now it can proudly bear the name for which it is best known, the golden tortoise beetle. You can learn more about the golden tortoise beetle in Bugguide.

One wonders how this little piece of gold and pink emerged from such ugly, dirty grub. Keep checking those morning glories, you may be rewarded by its sight, just remember, it is no bigger than a tiny gob of pink nail polish.