Curious questions, small bugs, big answers
- Author
- Staff
- Date
- August 10, 2021
We often get great questions about insects during our programs based on their observations of these small creatures. We took the chance to ask Allen, our entomologist, to answer some frequently asked questions about insect bodies.
Do insects have blood?
In a sense they do, but it is quite different from human blood. Insects have an open circulatory system, which means their “blood” does not flow through vessels like veins and arteries. Their body cavities are filled with a fluid called hemolymph which is moved through the body by contracting their muscles and through the dorsal vessel along their backs which functions like a heart. Hemolymph, like blood, plays a role in storing and transporting nutrients, hormones, and immune system cells throughout the body. Unlike blood, hemolymph does not contain red blood cells or oxygen carrying hemoglobin. Instead, insects breathe through a set of branching tubes called tracheae. The tracheae open to the outside at pores along the sides of an insect known as spiracles and branch out to reach every cell within the body.
The dorsal vessel is visible in these freshly hatched Madagascar hissing cockroaches (Gromphadorhina portentosa). Over time the cuticle will tan and stiffen as crosslinks form between chitin molecules.
If insects don’t have a skeleton how do they move?
To answer this question, we need to first clarify that insects do have a skeleton. They do not have an internal skeleton like we do, known as an endoskeleton. Rather, the outside of their bodies is their skeleton, an exoskeleton. Insect cuticle contains chitin, long chains of glucose molecules which when crosslinked provide rigidity allowing it to function as an exoskeleton. It turns out that insect exoskeletons play a similar role in movement as our endoskeletons do. Both kinds of skeletons have ridges or other structures for muscles to attach to. Insects move by contracting opposing muscles attached to their skeletons just like we do, the difference being the muscles are attached on the inside of their skeletons rather than the outside.
How many wings can an insect have?
Insects can have up to two pairs of wings, so four in total. Not all insects have wings and those that do only have them in their final adult life stage, except for mayflies which have two adult stages. Knowing that, notice any inaccuracies with the “Baby Bumble Bee” song? A baby bumble bee does not have a stinger or wings, they are just little white grubs! Some groups of insects never have wings, even as adults, like silverfish and fleas. Others have almost all winged adults like dragonflies, grasshoppers, butterflies, bees. In some groups wingless adults are more common like in cockroaches, crickets, wasps, moths, and even flies. Some insects have a modified pair of wings. Beetle forewings are modified into hard shells called elytra. Flies appear to only have one pair of wings because their hindwings are reduced to little nubs called halteres which aid in balance. The scientific name for the group flies belong to is Diptera which translates to “two wings”.
This dogbane beetle (Chrysochus auratus) at first glance may look wingless. The hard shell covering its abdomen are elytra, the beetle’s forewings. Underneath the elytra are a pair of membranous forewings used for flight.