Mike wrote to the “Consult-Ant” with a number of questions about ants. I am going to try to answer each one in a separate post. For the original list of questions and links to all answers, visit here.
9) Ants(obviously) eat other insects, and I probably lack observation skills but do the ants also eat the exoskeleton also? Do they (or the larvae) have some way of digesting chitin? I did see that the ants pretty much leave MOST of the exoskeleton intact, and go for soft parts.
You have definitely got some challenging questions here. I’m going to give this one a try, but if anyone knows more about this, please jump in.
You probably have seen bug bits (discarded exoskeletons) littering the trash heaps around ant nests.
Many arthropods, including insects, have long chain polysaccharides in their cuticle known as chitin. (Chitin is also found in fungi, which was one of the lines of evidence that moved fungi into their own Kingdom.) The exoskeleton of insects is also made up of various proteins and waxes.
Chitin is known to be difficult to digest. It’s long chain polysaccharide structure is similar to cellulose, which is also difficult for animals to use as food. The digestion of chitin requires special enzymes, chitinases, to break the strong bonds between the molecules. For a time it was thought that chitinases only occurred in a few bacteria, but evidence is showing up that certain animals have chitinases in their digestive systems, too.
It turns out that insects have chitinases able to break down chitin, but they aren’t where you might expect them. The chitinases in insects are in the cuticle and are used to move chitin during molting.
We know that adult worker ants can’t digest solids, so they can’t digest chitin. What about larvae? It is highly unlikely, because the larval digestive system is also lined with chitin. When insects molt, they also shed most of their digestive tract, which is derived from the same tissues as the exoskeleton. Therefore, it seems larval ants probably couldn’t digest chitin without digesting their own alimentary canal.
Many arthropod predators of insects suck out the insects fluid insides. Think about spiders, assassin bugs, lacewing larvae, etc. They are all feeding on fluids.
If it is true that insects can’t digest chitin as a food source, this leads to some other questions. Leafcutter ants feed on special fungi, which they grow in their nests. Do the fungi they grow have chitin? Do the leafcutters have gut symbionts or some other means to digest that chitin?
If there are any chitin experts out there, it would be great to have some clarification.