#18: Spiracles and Tracheae

Litinsects #18: Spiracles and Tracheae

Take a breath in... and out. Have you ever wondered how insects breathe? They don’t have lungs like we do. In fact they use a completely different respiratory system than vertebrates.

Insects breathe through SPIRACLES, which are small holes in the exoskeleton along the thorax and abdomen. A tiny “door” to the spiracle can be opened and closed to reduce water loss

Connected to the spiracles is a network of TRACHEAL TUBES that extend throughout the body. Gas exchange occurs by DIFFUSION across the walls of the smallest tubes.

In insects, the respiratory system is SEPARATE from the cardiovascular system. Their “blood” does not carry oxygen to cells (technically they don’t have blood but a future post will go into that more)

Some insects have collapsible internal sacs to store air for when their spiracles are closed. Aquatic insects use these air reserves while under water and can regulate buoyancy with the air sacs

The coolest thing is, although tracheae extend internally, they are actually invaginations of the exoskeleton so they are still covered by hardened cuticle. When the individual molts, these tubes are also shed. This photo shows these long thin tracheal tubes still connected to a shed exoskeleton (EXUVIA) of an assassin bug.

Photo: © Brandon Thorpe

Comments

#4: Simple Eyes

Litinsects #4: Simple Eyes Yesterday I talked about compound eyes, the multi-faceted structures that most insects use to see the world 👀 But insects actually have another visual system as well, composed of simple eyes or OCELLI. Unlike compound eyes, ocelli are composed of only one structure which makes them comparatively “simple” although they are still very important. These are light-detecting organs consisting of a single lens with sensory cells. They can detect movement but don’t form complex images. “Ocellus” comes from the Latin word oculus, meaning eye. So these structures are literally “little eyes” Ocelli are located on the insect’s head, usually between or adjacent to the compound eyes. They are usually dome-shaped, somewhat shiny structures In most flying insects (such as flies, dragonflies, bees, etc.) there tend to be three ocelli in a triangle arrangement (see photo). Some terrestrial insects (like cockroaches) have only two ocelli ...

#33: Hamuli

A row of hamuli on the wing of a bee The top two hamuli shown here are hooked onto the back edge of the forewing. Litinsects #33: Hamuli Today’s post is another on anatomy and is about a structure found in a group of insects that probably everyone around the world is familiar with... The order HYMENOPTERA is comprised of bees, wasps, sawflies, and ants. (Yes, ants are actually related to bees and wasps.) At around 150,000 described species it is among the top 4 largest group of insects (along with beetles, flies, and butterflies). One defining characteristic of hymenopterans are HAMULI (see photos). Hamuli (singular hamulus) are microscopic hook-like structures on the front surface of the rear wing that hook into the back edge of the front wing. This system interlocks the two wing pairs during flight, allowing them to beat in unison and act as one functional pair of wings. Basically hymenopterans have developed an anatomical wing coupling feature to enhance flight efficiency. (In the t...

#34: Insect Wings

Dragonfly wings Dipteran (fly) wing Monarch butterfly wing Lacewing wings Litinsects #34: Insect Wings Let’s talk wings. The ability to fly has existed in only 4 groups of animals: birds , bats , pterosaurs , and of course insects . The first three groups, all vertebrates, each evolved flight independently (in other words, they have no winged ancestor in common) and the wings replace a pair of limbs. Insect wings on the other hand, which first showed up around 400 million years ago, are not derived from legs but are completely separate structures. The big debate about the evolution of insect wings is whether they developed from pre-existing structures (like gills or extensions of the thorax) or were entirely new structures. There is very little fossil evidence documenting this evolutionary transition so no one has yet definitively answered this question... Insect wings attach to the second and third thoracic segments. At rest they may be held vertically over the back, horizontally ou...

Litinsects

Search This Blog