The recent wet weather in Iowa has prompted people to ask me if insects can breathe under water. In short, most insects can survive under water (or in saturated soils) for short durations. Of course, how insects can accomplish this is complicated and full of entomological jargon. In some ways, insects breathe like us and in other ways, insects breathe in a completely different way.
How are we the same?
Insects get oxygen from the air to fuel muscles and tissues. Those insects that move a lot, particularly through flight, need more oxygen than sedentary insects. Eventually, insects release carbon dioxide as waste back into the air.
How are we different?
Humans have a combined respiratory and circulatory system, where oxygen is moved in the blood to muscles and tissues within a closed system. For insects, respiration is separate from the circulatory system. Oxygen and carbon dioxide gases are exchanged through a network of tubes called tracheae. Instead of nostrils, insects breathe through openings in the thorax and abdomen called spiracles. Insects that are diapausing or non-mobile have low metabolic rates and need to take in less oxygen.
How are they better?
Insects have a more efficient respiratory system than humans. They can take in greater volumes of oxygen, in proportion to the body size, than we can. Most insects can open and close the spiracles and experience “discontinuous gas exchange.” What? Basically, insects with closed spiracles recycle the oxygen in the tracheae and are able to survive without constant breathing. This is a huge advantage for those insects experiencing stress, like soil-dwelling insects in hypoxic conditions. How long insects can survive without fresh oxygen depends on the species and life stage (and many other things beyond this blog post).
For example, 50% of 2nd/3rd instar western corn rootworms die after 42 hours of hypoxic conditions at 59°F.
Insects that live part of their lives in the water
The eggs, larvae and often the nymphs of many aquatic insect species develop in the water. The pupae then leave the water so that they can fly away as adults. The pupae and adults feed in different environments, which reduces competition between them. For example, adult dragonflies are land predators and do not hunt the same prey as their offspring in the water. Others, such as mayflies and dobsonflies, accumulate energy in the larval stages. Once they reach adulthood, they no longer eat – they just reproduce on land!
Many species of insects spend their whole lives in the water. For some of them, the eggs, larvae and pupae develop in the water, while others live in mud along the shoreline. In all cases, the adults maintain an aquatic lifestyle. At this stage, many are active both in the air and in the water.