Review: Principles of Insect Morphology

RE Snodgrass first published Principles of Insect Morphology in 1935. Several reprints and 70 years later, this text still is useful and interesting for a student of entomology, and is a wonderful reference for any entomologist to have. Yes, it does not have the molecular information that one would find in more recent works such as Chapman's Insects: Structure and Function. At one point Snodgrass refers to the germ cells as "the carriers of inheritance, whatever that may be". Modern understanding of inheritance through DNA was not discovered until the middle part of the 20th century.

However, the drawings are excellent, and our understanding of basic structures of the insects such as the general body plan, the sclerites, muscles, wings, digestive tract, etc, have not changed much since this book was published. The writing and explanation of the figures is also excellent, and Snodgrass' hypotheses for the evolution of the insect ground plan are still in use today.

Snodgrass was a very meticulous, ordered and organized character. His daily habits were regular, he would fill his coffee cup to the same exact line every day at the same time and walk the same 30 some steps down the hallway to his office. This understanding of order and attention to detail shows very well in his drawings. His particular style of work was to reduce figures to the smallest necessary number of lines to convey proper understanding of structures. Those of you who have worked in biology labs before understand that too much detail in a reference figure obscures understanding of the position and structure of the very parts which you are using as reference. By reducing lines, Snodgrass effectively conveyed the exact message he wished to with his drawings, rather than putting us in awe of his artistic work and scrambling to understand what goes where.
Above: An example of Snodgrass' drawing style. Note the lack of stipling except to differentiate membrane from sclerotized regions.


Principles of Insect Morphology is a book every entomologist should have, as a reference text, and simply for the pleasure of its excellence. It is as useful now as it was 70 years ago.

Amazon.com link for Principles of Insect Morphology

Tapes of three lectures by RE Snodgrass with transcripts and drawings

Oxyethira video (Hydroptilidae)

I found this video on youtube of the larvae of the genus Oxyethira of the microcaddisfly family (Hydroptilidae). Hydroptilids are the worlds smallest caddisflies, and happen to be the largest family of Trichoptera, with over 1400 named species worldwide. This particular video shows the fifth instar larvae. I know this because during the first through 4th larval instars, Hydroptilids are free living and do not make a case. When they molt to the 5th instar, their abdomens become much larger and sometimes grow to bizarre shapes, and they also produce a portable case in which they eventually pupate. These cases are usually unique for each genus. Oxyethira makes a wine bottle shaped case of silk, in which one end is a narrow neck and the other like the base of a wine bottle. Both sides are open, and as you can see in the video the larvae can easily switch sides from inside the case.



Above: The common genus Hydroptila. The cases are constructed of sand and silk, and have a characteristic, slightly angled "roof" on one seam.

Chathamiidae: The Marine Caddisflies

Yesterday I took a broad stance on why I am passionate about Trichoptera, and why they are ceaselessly interesting. Today I would like to focus down and examine a specific family of caddisflies from all angles, a taste of how unusual the life cycles and behavior of some trichoptera can become.

The Chathamiidae (named after the Chatham Islands in New Zeland) are a small family of caddisflies, only 2 genera and five species. All Chathamiids inhabit tidepools in their larval stage, the only insect found thus far that has colonized these habitats. They can be found on the Southern coasts of Austrailia, the coasts of New Zealand, and the Chatham and Kermadec Islands.

For many reasons, aquatic insects have failed to colonize the oceans. It is more than just a matter of osmotic potential, the high salt content of sea water. It is also a matter of competitive exclusion. Ocean invertebrate niches are well filled, there are very few openings for invasion by insects. However, at least 5 species have found a place in this environment. (Note: There is also a genus of marine water striders that can be found quite far from land, but these are not considered fully aquatic in the sense that Chathamiids are.)

The life cycle of marine caddisflies is quite amazing in its own right. In the species Philanisus plebeius, larvae begin their lives as eggs oviposited within the body cavity of the Australian cushion star Patiriella exigua. After more than 30 days the larvae hatch and exit their hosts through the stomach and out the mouth. They then spend 7 larval instars feeding within the tide pools on red calciferous algae in full sunlight. There are several odd things about this. One, the normal number of larval instars, that is, the normal number of times that a Trichopteran larvae molts before pupation is 5. Two, these are the only caddisflies known to feed in tide pools on calcified algae, and three, they feed in full sunlight, while most caddisfly larvae are rather secretive and tend to feed in shaded regions.

Marine caddisflies construct portable cases of tough silk, tubes to which they attach various algal fragments, supposedly for camouflage. Larvae pupate on the red alga Corallina officianalis. Adults fly on the open coast through out the summer. The females have long pointed ovipositors that are able to penetrate the cushion stars that serve as hosts for the larvae.

Unfortunately, no one has supplied any photographs of marine caddisflies, larvae or adults, to the internet. If anyone finds a photograph of the larvae, especially their case, I would love to see it.

Riek EF. 1976. The marine caddisfly family Chathamiidae (Trichoptera). Australian Journal of Entomology, 15: 405-419. (PDF; with drawings and keys)

Ward J. 1994. The New Zealand marine caddisflies (Trichoptera). Weta, 17: 18-20. (PDF)

Winterbourn M, Anderson N. 1980. The life history of Philanisus plebeius Walker (Trichoptera: Chathamiidae), a caddisfly whose eggs were found in a starfish. Ecological Entomology, 5: 293-304.

An Introduction to Trichopterology

Trichopterology is the study of caddisflies, an amazing order of insects with which I am truly enamored. The scientific name for these insects comes from the Greek Trichos for hair and Pteros for wing. Caddisflies as adults are terrestrial, hairy winged organisms which are very moth-like in appearance. Their manners are relatively secretive, flying at night, and can often be found in large numbers around outdoor lights. They do not feed as adults, unlike their close relatives the butterflies, they have only vestigial mouthparts. From the above description, some may say these creatures are wholly uninteresting, of no use economically, not an agricultural pest nor a vector of diseases, nothing more than bat food.

The larvae of these creatures, however, are an entirely different story. All immature caddisflies are fully aquatic with few exceptions. These are underwater caterpillars thriving in freshwater of all kinds around the world. These are the underwater architects (as the great Trichoptera taxonomist GB Wiggins called them in his book of the same name), whom construct incredible wonders beneath the surface of the water all around us, cases of silk, of wood, leaves, stones, which they carry around with them. Others create masterful nets of silk with meshes so fine they put our human counterparts to shame. The range of ecologies within this order is immense, from dentritovores to herbivores, omnivores and even predators, and their diversity of habitats is just as great. All freshwater habitats, from glacial waterfalls to springs and seeps, to rivers, streams, lakes, temporary pools, all have become habitats for these marvels; they are found in all faunal regions except the antarctic. Caddisflies have even taken this one step further: they are the only insect that has (at least partially) found a niche in the marine environment.

So why should you be interested? For their amazing behavior of spinning silk into underwater masterpieces? For their range of habitats and ecologies? If nothing else, you should be interested for the impact they have on our lives as humans, as members of aquatic ecology, as a link in our fisheries food chain, as a canary in the well for the damage we have done to our waters, and finally, as a biomonitoring tool to help us correct our wrongs to the natural world.

I wish to discuss all this and more in great detail as time continues. When you are passionate about life, you feel the need to share that passion.


A note: I do understand that the correct term would be "Trichopterist". My usage of Trichopterologist is a pun against myself, in the same way I might call myself a "scientician". A person needs the ability to laugh at them self when they are pursuing something they are truly passionate about, or otherwise they become too serious, and they loose that passion. A good nature of fun along with discipline and dedication is important for any person in this world.

An Obsession for Caddisflies.

My whole life, I have been interested in insects. The joke is I was born into entomology. My mother was running around with an butterfly net while she was pregnant with me. From early childhood I was collecting insects, laying pit traps in the garden, setting out lights to attract moths. My dad and I would go out to a local pond and catch crepuscular dragonflies by twilight.

During my middle school and high school years I forgot about this passion. I had other worries, other interests. During my undergraduate education, I fell back into love with biology, entomology, and found a new love in aquatic insects. I was already halfway to completing my degree in aquatic biology when I realized how much I loved those bugs! Thankfully it was not too late for me. After a summer working under an aquatic entomologist, I knew I had found my lifelong passion in caddisflies. I am now a graduate student researching what I love. Caddisflies have become my obsession, and along with biology, evolution, freshwater ecology, invertebratology, entomology and other random science nerdery, this will be the focus of my blog. Its outreach on my part, to show the world what I love and why I love it. Its also an attempt to journal my research and my progress as a student of biology.

Next time: An introduction to Trichopterology.